US20180339153A1 - Steering an implantable medical lead via a rotational coupling to a stylet - Google Patents

Abstract

An implantable medical lead has a torsional stiffness and is rotationally coupled to a stylet. Applying rotation directly to the lead in turn causes rotation of the stylet. Where the stylet has a bent tip for purposes of steering the lead, the rotation applied to the lead rotates the bent tip so that the lead can be steered by rotating the lead rather than rotating a hub of the stylet. The rotational coupling may be achieved through one or more features provided for the lead and/or the stylet, such as a feature within a lumen of the lead that mates to a feature along the stylet or a feature of the stylet hub that engages the proximal end of the lead. The torsional stillness of the lead may be provided by adding a feature within the lead body, such as a braided metal wire or an overlapping foil.

Description

RELATED CASES
• The present application claims priority to and incorporates by reference the following, each as if rewritten herein in its entirety: U.S. Provisional Application 61/174,204 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,216 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,224 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,234 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,247 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,254 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,262 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,276 filed on Apr. 30, 2009; U.S. Provisional Application 61/174,287 filed on Apr. 30, 2009; and U.S. Provisional Application 61/174,296 filed on Apr. 30, 2009.
TECHNICAL FIELD
• Embodiments relate to the steering of implantable medical leads during implantation. More particularly, embodiments relate to steering of implantable medical leads via a rotational coupling of the implantable medical lead to a stylet.
BACKGROUND
• Implantable medical systems including implantable medical devices (IMD) and associated implantable medical leads provide functions such as stimulation of muscle or neurological tissue and/or sensing of physiological occurrences within the body of a patient. Typically, the IMD is installed in a subcutaneous location that is accommodating and relatively accessible for implantation. For instance, to provide stimulation near the spine or pelvis, the IMD may be installed in a pocket located on the abdomen or upper buttocks region of the patient. The implantable medical lead is installed either through a percutaneous procedure or a surgical procedure, depending upon the type of lead that is necessary.
• For a percutaneous implantation procedure, the implantable medical lead is inserted via an introducer needle that provides a passageway for the lead to enter the body. The lead is fed through the introducer needle, and a distal end of the lead is steered along a desired path until reaching the stimulation site. To force the lead though the body to the stimulation site, a stylet is inserted into a lumen of the lead. One stylet may have a straight distal end to force the lead in a straight direction while another stylet may have a bent distal tip to urge the lead to turn in a particular direction.
• The doctor implanting the lead may steer the lead by rotating a stylet hub on the proximal end of the stylet. The stylet is torsionally stiff so that rotating the stylet hub on the proximal end results in the bent tip on the distal end rotating as well. The doctor rotates the stylet hub until the distal tip has rotated to a position that will urge the lead in the desired direction. Insertion force is applied to the lead to move the lead in the desired direction. When a new direction is needed, the doctor reaches back to the end of the stylet to again rotate the stylet hub.
• While steering the lead with the stylet hub is effective at rotating the distal tip of the stylet, it can be cumbersome for the doctor. The doctor works directly with the lead at the site of the introducer needle to apply an insertion force, but the remainder of the lead to be implanted, and hence the remainder of the stylet, may extend behind the doctor for a significant distance. Thus, the doctor may have to reach back to the proximal end of the lead to grasp the stylet hub each time a steering input is needed. Reaching back and forth between the lead at the introducer needle and the stylet hub can be time consuming and burdensome.
SUMMARY
• Embodiments address issues such as these and others by providing a rotational coupling between a torsionally stiff lead and a stylet. The torsional stiffness of the lead allows rotation of the lead body when a point on the lead body is being rotated. The rotational coupling between the torsionally stiff lead body and the stylet allows the rotation being applied to the point on the lead body to be imparted to the stylet. Thus, when a doctor rotates the lead body at the site of the introducer needle, the distal tip of the stylet also rotates without the doctor being required to apply the rotation to the stylet hub. The doctor can thereby steer the lead body by applying rotation directly to the lead body.
• Embodiments provide a method of guiding an implantable medical lead. The method involves providing the implantable medical lead with a torsional stiffness over a length of the implantable medical lead, the torsional stiffness being sufficient to impart rotation over the length when rotation is applied at a point along the length that includes the torsional stiffness. Upon insertion of a stylet with a distal guide bend into a lumen of the implantable medical lead, a rotational coupling of the stylet to the implantable medical lead is provided such that imparting rotation to the implantable medical lead at the point along the length imparts rotation to the stylet to direct the distal guide bend.
• Embodiments provide an implantable medical lead kit that includes an implantable medical lead with a torsional stiffness over a length of the implantable medical lead, the torsional stiffness being sufficient to impart rotation over the length when rotation is applied at any point along the length that includes the torsional stiffness. The implantable medical lead kit further includes a stylet within a lumen of the implantable medical lead, the stylet being rotationally coupled to the implantable medical lead when present within the lumen such that imparting rotation to the implantable medical lead at one or more points along the length imparts rotation to the stylet to direct the distal guide bend.
• Embodiments provide a method of guiding an implantable medical lead. The method involves inserting a stylet with a distal guide bend into a lumen of the implantable medical lead to rotationally couple the stylet to the implantable medical lead such that imparting rotation to the implantable medical lead at one or more points along the length imparts rotation to the stylet. The method further involves directing the implantable medical lead in a desired direction by imparting rotation to the implantable lead to cause rotation of the stylet to a desired rotational position, wherein the distal guide bend urges the implantable medical lead in the desired direction. Insertion force is applied to the implantable medical lead.
DESCRIPTION OF THE DRAWINGS
• FIG. 1 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 2A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 2B shows the embodiment of the implantable lead in cross-section to reveal the shield and filars.
• FIG. 2C shows an embodiment of the implantable lead with the shield revealed and with various parameters being specified.
• FIG. 2D shows an embodiment of the implantable lead with dual braid wire windings.
• FIG. 2E shows an embodiment of the implantable lead with braid wires having a round cross-section.
• FIG. 2F shows an embodiment of the implantable lead with braid wires having a rectangular cross-section.
• FIG. 2G shows an embodiment of the implantable lead with braid wires having an oval cross-section.
• FIG. 2H shows an embodiment of the implantable lead with the lead terminating at a given spacing from a nearest connector and a nearest electrode at the proximal and distal ends.
• FIG. 3 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 4A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 4B shows the embodiment of the implantable lead in cross-section to reveal the shield and filars.
• FIG. 4C shows an example of the implantable lead with a portion of the shield exposed near a proximal end of the implantable lead.
• FIG. 4D shows an example of the implantable lead with an external electrode providing a coupling to the shield.
• FIG. 5A shows a side view of an embodiment of an implantable medical system where the shield of the lead is grounded to a can of the IMD.
• FIG. 5B shows an end view of the embodiment where the lead passes through a connection block having a set screw to ground the shield to the can.
• FIG. 5C shows an end view of the embodiment where the lead passes through a connection block having a spring loaded connector to ground the shield to the can.
• FIG. 6 shows an example of a spring loaded connector.
• FIGS. 7A-7C show side views of embodiments of an implantable medical system where the shield is grounded with an external wire to the can over a direct current pathway.
• FIGS. 8A-8C show side views of embodiments of an implantable medical system where the shield is grounded with an external wire to the can over a capacitively coupled pathway.
• FIGS. 9A-9F show side views of embodiments of an implantable medical system where the shield is grounded within a header of the IMD to the can.
• FIGS. 10A-10C show side views of embodiments of an implantable medical system where the shield is grounded to a ground plate on the header of the IMD.
• FIG. 11 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 12A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 12B shows the embodiment of the implantable lead in cross-section to reveal the shield and filars.
• FIG. 12C shows an example of the implantable lead with a portion of the shield exposed at a point distant from the distal end of the lead.
• FIG. 12D shows an example of the implantable lead with an external electrode providing a coupling to the shield at a point distant from the distal end of the lead.
• FIG. 12E shows an example of the implantable lead with a portion of the shield nearly exposed at a point distant from the distal end of the lead.
• FIG. 12F shows an example of the implantable lead with a portion of the shield exposed or nearly exposed at a plurality of points distant from the distal end of the lead.
• FIG. 12G shows an example of the implantable lead with a plurality of external electrodes providing a coupling to the shield at a plurality of points distant from the distal end of the lead.
• FIG. 12H shows the embodiment of the implantable lead in cross-section to reveal the shield and the external metal conductor in contact with the shield.
• FIG. 12I shows the embodiment of the implantable lead in cross-section to reveal the exposed shield.
• FIG. 12J shows the embodiment of the implantable lead in cross-section to reveal the shield and the metal conductor nearly contacting the shield.
• FIG. 12K shows the embodiment of the implantable lead in cross-section to reveal the nearly exposed shield.
• FIGS. 13A-13C show metal conductors of various types for attachment to a lead to provide a coupling to the shield.
• FIGS. 13D-13F show metal conductors having various configurations of non-conductive coatings for attachment to a lead to provide a coupling to the shield.
• FIG. 14A shows the embodiment of the implantable lead in cross-section to reveal the shield and an outer doped jacket layer.
• FIG. 14B shows the embodiment of the implantable lead with a plurality of points with the outer doped jacket layer.
• FIG. 14C shows an embodiment of the implantable lead in cross-section to reveal the shield and a doped jacket layer at the shield.
• FIG. 14D shows the embodiment of the implantable lead with a plurality of points with the doped jacket layer at the shield.
• FIG. 15A shows an embodiment of the implantable lead having a lead anchor coupled to a metal conductor to provide the RF pathway to ground.
• FIG. 15B shows the embodiment of the implantable lead in cross-section to reveal the shield, the metal conductor, and the lead anchor.
• FIG. 15C shows an embodiment of the implantable lead having a lead anchor coupled directly to the shield to provide the RF pathway to ground.
• FIG. 15D shows the embodiment of the implantable lead in cross-section to reveal the shield and the lead anchor.
• FIG. 15E shows an embodiment of the implantable lead having a lead anchor with a non-conductive coating.
• FIG. 16 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to an extension containing a shield which is coupled to a lead containing a shield.
• FIG. 17A shows an embodiment of an implantable extension coupled to an implantable lead with the shield of each revealed.
• FIG. 17B shows an embodiment of a coupling of the implantable lead and extension in cross-section to reveal the shield, shield electrode, and filars of the lead and a shield connector and jumper wire of the lead extension.
• FIG. 17C shows an embodiment of a coupling of the implantable lead and extension in cross-section to reveal the shield, shield electrode, and filars of the lead and a shield connector and shield of the lead extension.
• FIG. 17D shows an embodiment of a coupling of the implantable lead and extension in cross-section to reveal the filars, filar jumper, and filar electrode of the lead and a filar connector, filar jumper wire, and shield jumper wire of the lead extension.
• FIG. 17E shows an embodiment of a coupling of the implantable lead and extension in cross-section to reveal the filars, filar jumper wire, and filar electrode of the lead and a filar connector, filar jumper wire and shield of the lead extension.
• FIG. 17F shows an embodiment of an implantable extension coupled to an implantable lead where a jumper wire interconnects the two shields.
• FIG. 17G shows an embodiment of an implantable extension coupled to an implantable lead where the shield of the extension extends to the shield connector of the extension to interconnect the two shields.
• FIG. 18 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 19A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 19B shows the embodiment of the implantable lead in cross-section to reveal the shield and filars.
• FIG. 20 shows an embodiment of the implantable lead where the shield terminates at a butt joint to an insulation extension.
• FIG. 21 shows an embodiment of the implantable lead where the shield terminates at a scarf joint to an insulation extension.
• FIG. 22 shows one example of a set of steps to create the implantable lead ofFIGS. 20 and 21.
• FIG. 23 shows an embodiment of the implantable medical lead where the shield terminates at a lap joint to an insulation extension.
• FIG. 24 shows one example of a set of steps to create the implantable lead ofFIG. 23.
• FIG. 25 shows an embodiment of the implantable medical lead where the shield terminates at a ring within a lap joint.
• FIG. 26 shows an embodiment of the implantable medical lead where the shield terminates at a ring at a butt joint.
• FIG. 27 shows an embodiment of the implantable medical lead where wires of the shield fold over individually at the termination point.
• FIG. 28 shows an embodiment of the implantable medical lead where a joint at the shield termination includes a barbed connection to an inner insulation layer.
• FIG. 29 shows an embodiment of the implantable medical lead where a joint at the shield termination includes a barbed connection to an inner insulation layer.
• FIG. 30 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 31A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 31B shows the embodiment of the implantable lead in cross-section to reveal the shield and filars.
• FIG. 32 shows an embodiment of the implantable lead where the shield terminates to a metal connector near a butt joint to an insulation extension.
• FIG. 33 shows an embodiment of the implantable lead where the shield terminates to a metal connector near a scarf joint to an insulation extension.
• FIG. 34 shows one example of a set of steps to create the implantable lead ofFIGS. 32 and 33.
• FIG. 35 shows an embodiment of the implantable medical lead where the shield terminates to a metal connector near a lap joint to an insulation extension.
• FIG. 36 shows one example of a set of steps to create the implantable lead ofFIG. 35.
• FIG. 37 shows an embodiment of the implantable medical lead where the shield terminates between a pair of metal connectors near a joint to an insulation extension.
• FIG. 38 shows an alternative embodiment where a top metal connector of the pair has sharp features to penetrate an outer insulation layer.
• FIG. 39 shows an embodiment of the implantable medical lead where the shield terminates between a pair of metal connectors near a lap joint to an insulation extension.
• FIG. 40 shows an alternative embodiment of the implantable medical lead where an inner metal connector is mounted flush with an inner insulation layer.
• FIG. 41 shows one example of a set of steps to create the implantable lead ofFIGS. 37-40.
• FIG. 42 shows an embodiment of the implantable medical lead where the shield folds over to terminate between a pair of metal connectors near a joint to an insulation extension.
• FIG. 43 shows one example of a set of steps to create the implantable lead ofFIG. 42.
• FIG. 44 shows an embodiment of the implantable medical lead where the shield laps onto a metal connector near a joint to an insulation extension.
• FIG. 45 shows one example of a set of steps to create the implantable lead ofFIG. 44.
• FIG. 46 shows an embodiment of the implantable medical lead where the shield exits the insulation layers at a taper and terminates between a pair of metal connectors.
• FIG. 47 shows one example of a set of steps to create the implantable lead ofFIG. 46.
• FIG. 48 shows an embodiment of the implantable medical lead where wires of the shield fold over individually at the termination point at a metal connector.
• FIG. 49 shows a percutaneous implantation scenario of an embodiment of an implantable medical lead.
• FIG. 50 shows an implantable medical system configuration resulting from the percutaneous implantation ofFIG. 49.
• FIG. 51 shows an embodiment of the implantable medical lead that has a braided metal shield providing torsional stiffness.
• FIG. 52 shows a cross-section of an embodiment of the implantable medical lead where no rotational coupling exists to the stylet.
• FIG. 53 shows a cross-section of an embodiment of the implantable medical lead where a square-shaped rotational coupling exists to the stylet.
• FIG. 54 shows a cross-section of an embodiment of the implantable medical lead where a star-shaped rotational coupling exists to the stylet.
• FIG. 55 shows a cross-section of an embodiment of the implantable medical lead where a hexagonal-shaped rotational coupling exists to the stylet.
• FIG. 56 shows a proximal end of an embodiment of the implantable medical lead achieving a rotational coupling with a tapered feature of a stylet hub.
• FIG. 57 shows a proximal end of an embodiment of the implantable medical lead achieving a rotational coupling with a splined feature of a stylet hub.
• FIG. 58 shows a proximal end of an embodiment of the implantable medical lead achieving a rotational coupling with a threaded feature of a stylet hub.
• FIG. 59 shows an embodiment of an implantable medical system including an IMD and two leads, each with a radiopaque marker sutured to the lead.
• FIG. 60 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker sutured to the IMD case.
• FIG. 61 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker placed loosely in a pocket nearby the IMD and lead.
• FIG. 62 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker glued to the lead.
• FIG. 63 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker glued to the IMD case.
• FIG. 64 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker clamped to the lead.
• FIG. 65 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker clamped to the IMD case.
• FIG. 66 shows an embodiment of an implantable medical system including an IMD and a lead, with a radiopaque marker crimped to the lead.
• FIG. 67A shows an embodiment of an implantable medical system including a lead and a radiopaque coil being placed onto the lead in a radially expanded state.
• FIG. 67B shows an embodiment of an implantable medical system including a lead and a radiopaque coil once placed onto the lead in a radially contracted state.
• FIG. 68A shows the coil on an installation tool in the radially expanded state prior to placement on the lead.
• FIG. 68B shows the coil being placed onto the lead from the tool to achieve the radially contracted state.
• FIG. 69A shows an embodiment of a polymer structure that fits axially onto the lead and provides a radiopaque plate.
• FIG. 69B shows an embodiment of an implantable medical system where the polymer structure ofFIG. 69A is positioned on the lead.
• FIG. 69C shows an embodiment of an implantable medical system where an embodiment of a polymer structure that has an anchor format including suture wings and a radiopaque plate is sutured in place on the lead.
• FIG. 70A shows an embodiment of a polymer structure that fits axially onto the lead and provides a radiopaque coil.
• FIG. 70B shows an embodiment of an implantable medical system where the polymer structure ofFIG. 70A is positioned on the lead.
• FIG. 70C shows an embodiment of an implantable medical system where an embodiment of a polymer structure that has an anchor format including suture wings and a radiopaque coil is sutured in position on the lead.
• FIG. 71 shows an embodiment of the lead that includes a shield to provide safety during medical procedures such as an MRI scan.
• FIG. 72 shows the embodiment ofFIG. 71 in cross-section to reveal the shield, filars, and lumen.
• FIG. 73 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 74A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 74B shows an embodiment of an implantable lead with the shield having an axial cut that creates a slot.
• FIG. 74C shows an embodiment of an implantable lead with the shield having the axial cut but with the edges of the slot brought into an overlapping configuration to close the slot.
• FIG. 74D shows an embodiment of an implantable lead with the shield having the axial cut but with a shield patch applied across the slot.
• FIG. 75A shows the embodiment of the implantable lead ofFIG. 74A in cross-section to reveal the shield and filars.
• FIG. 75B shows the embodiment of the implantable lead ofFIG. 74B in cross-section to reveal the shield and the slot.
• FIG. 75C shows the embodiment of the implantable lead ofFIG. 74C in cross-section to reveal the shield having the overlapping edges.
• FIG. 75D shows the embodiment of the implantable lead ofFIG. 74D in cross-section to reveal the shield and the shield patch.
• FIG. 76A shows an embodiment of the shield as an equivalent tube to reveal a linear axial cut that produces a linear slot.
• FIG. 76B shows the embodiment of the shield as an equivalent tube to reveal the edges of the slot that overlap to close the slot.
• FIG. 76C shows the embodiment of the shield as an equivalent tube to reveal the shield patch that closes the slot.
• FIG. 76D shows an embodiment of the shield as an equivalent tube to reveal a helical axial cut forming a helical slot.
• FIG. 77 shows an embodiment of an implantable medical system that includes an implantable medical device (IMD) coupled to a lead containing a shield.
• FIG. 78A shows an embodiment of an implantable lead with the shield revealed.
• FIG. 78B shows the embodiment of the implantable lead ofFIG. 78A in cross-section to reveal the shield and filars.
• FIG. 79A shows one embodiment of a guard at the termination of the shield.
• FIG. 79B shows another embodiment of a guard at the termination of the shield.
• FIG. 79C shows another embodiment of a guard at the termination of the shield.
• FIG. 80A shows the embodiment ofFIG. 79A in cross-section to reveal first and second portions of the continuous shield forming a guard at the termination of the shield.
• FIG. 80B shows the embodiment ofFIG. 79B in cross-section to reveal first and second portions of the two-piece shield forming a guard at the termination of the shield.
• FIG. 80C shows the embodiment ofFIG. 79C in cross-section to reveal a first portion including first and second sub-portions and a second portion at the termination of the two-piece shield.
DETAILED DESCRIPTION
• Embodiments of implantable medical leads that include shields are disclosed herein. Ten primary subject matter topics are presented, where each new topic begins with reference toFIGS. 1, 3, 11, 16, 18, 30, 49, 59, 73, and 77. However, this detailed description should be read as a whole whereby subject matter of embodiments corresponding to one particular topic is applicable to embodiments corresponding to other topics.
• For instance, shield details disclosed in relation toFIGS. 1-2H are also applicable to the shields of all embodiments disclosed inFIGS. 3-80C where such shield details may be desired. The examples of grounding a shield within a lead as disclosed in relation toFIGS. 3-15E are applicable to all embodiments disclosed herein where a grounded shield may be desired. The examples of shielding the extension and interconnecting the shielding of the lead to the extension as disclosed in relation toFIGS. 16-17G are applicable to all embodiments disclosed herein where inclusion of a shielded extension may be desired. The examples of terminating the shield as disclosed in relation toFIGS. 18-48 are applicable to all embodiments disclosed herein where terminating the shield within the lead body may be desired. The examples of rotationally coupling the lead body to a stylet as disclosed in relation toFIGS. 49-58 are applicable to all embodiments disclosed herein where such rotational coupling may be desired. The examples of markers for the lead as disclosed in relation toFIGS. 59-72 are applicable to all embodiments disclosed herein where such a marker may be desired. The examples of breaking the circumferential mechanical continuity of the shield as disclosed inFIGS. 73-76D are applicable to all embodiments disclosed herein where such a lack of continuity may be desired. The examples of guarding the termination of the shield as disclosed inFIGS. 77-80C are applicable to all embodiments disclosed herein where a guarded shield termination may be desired.
• Embodiments disclosed in relation toFIGS. 1-2H provide for radio frequency (RF) shielding of an implantable lead that may be connected to an implantable medical device (IMD). A shield is present within the jacket of the implantable lead. The shield is designed to provide RF shielding while also providing various mechanical properties suitable for implantation.
• FIG. 1 shows an example of an implantablemedical system1100 that includes anIMD1102 coupled to alead1108. TheIMD1102 includes ametal can1104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD1102 includes aheader1106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can1104. Theheader1106 is shown transparently for purposes of illustration. Theheader1106 provides a structure for securing thelead1108 to theIMD1102 and for establishing electrical connectivity between circuitry of theIMD1102 and electrodes of thelead1108.
• Thelead1108 includeselectrodes1116 on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings1110 on a proximal end that is positioned within theheader1106. The connector rings1110 make physical contact withelectrical connections1111 within the header. Theelectrical connections1111 may include a metal contact that theconnector ring1110 rests against upon being inserted into theheader1106 where a wire extends from the metal contact into thecan1104 where the circuitry is housed. Signals applied by theIMD1102 to the connector rings1110 are conducted through thelead1108 to theelectrodes1116 to provide the stimulation therapy to the patient.
• Thelead1108 is secured in theheader1106 such as by aset screw block1112 within theheader1106 that allows at least oneset screw1114 to be tightened against at least one of the connector rings1110. Ashield1118 such as the one discussed below with reference toFIGS. 2A and 2B is located within thelead1108. Theshield1118 may or may not be grounded to the metal can1104 at theIMD1102 ofFIG. 1 or at various points along the length of the lead. Theshield1118 may or may not be grounded through other mechanisms as well. For instance, theshield1118 may be located within thelead1108 at a small distance from the surface so that theshield1118 will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length.
• FIGS. 2A and 2B show an example of thelead1108, where ashield1118 is present. Anouter jacket layer1120 is shown transparently inFIG. 2A for purposes of illustrating theshield1118. Theshield1118 blocks at least some RF energy from directly coupling toconductive filars1124 that are present within thelead1108. Theconductive filars1124 extend the length of the lead and interconnect the proximal connector rings1110 to thedistal electrodes1116 so that stimulation signals are conducted from the proximal end to the distal end of thelead1108.
• As shown inFIG. 2A, theshield1118 of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. The metal braid wire may be a biocompatible metal, particularly for embodiments where a portion of theshield1118 may be exposed for purposes of grounding. Biocompatible metals ensure that if theshield1118 is exposed to tissue, either by design or due to wear on thelead1108, theshield1118 does not become a toxin to the patient.
• As shown inFIG. 2B, theshield1118 may be embedded within the jacket of thelead1108. One manner of constructing thelead1108 with theshield1118 is to provide a jacket that includes an inner layer ofinsulation1122 that isolates aninner region1121 where thefilars1124 and anyadditional insulation layer1126, such as polytetrafluoroethylene (PTFE) that may surround each filar1124 are located. According to some embodiments, thisinner layer1122 may have apost-assembly thickness1130 of at least 2 mils and may be significantly larger such as 5 or 6 mils depending upon size constraints for thelead1108 and/or the size of theouter layer1120. Theshield1118 may then reside on the outer portion of theinner layer1122, and the jacket's outer layer ofinsulation1120 may then enclose theshield1118. Theouter layer1120 provides anoverall lead diameter1134. Theouter jacket1120 maybe added over thebraid1118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield1118 to RF couple to tissue, typically as capacitive coupling, either as an alternative to grounding at the can of the IMD or specific points along the length or in addition to grounding at the can or along the length, the entireouter jacket layer1120 may be relatively thin, particularly for the portion passing over the braid wires of theshield1118. According to the various embodiments apost-assembly thickness1132 for the portion of theouter layer1120 passing over a single braid wire may be on the order of 0.5 to 5 mils. The thickness of theouter layer1120 over theshield1118 is reduced by a braid wire diameter at points where braid wires intersect. Accordingly, thepost-assembly thickness1132 over the single wire may vary depending upon a chosen braid wire diameter so that adequate coverage also exists at the intersection points. Furthermore the thickness may be less than 0.5 mils, particularly where tissue in-growth is not of concern and in that case theouter layer1120 could be omitted.
• This thickness of theouter layer1120 over the braid wires may also vary depending upon the type of metal used for the braid wires. For instance, it has been found that the thickness of theouter layer1120 has less of an impact on the heating at the electrode when using a titanium braid wire than when using a tantalum wire with all else being equal. However, with anouter layer1120 whosepost-assembled thickness1132 is on the lower side of the range, such as 2 mils or less, tantalum braid wires may allow for less heating at the electrodes than if titanium braid wires are used.
• Where theshield1118 grounds at thecan1104 and/or at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, theshield1118 may be located further from the outer surface of thelead1108. This increased depth of theshield1118 within the jacket may provide for a moredurable lead1108 in terms of protecting the braid wires in areas of high flexure and motion, such as in the lumbar spine.
• The inner andouter jackets1122,1120 may be constructed of the same or similar materials such as various flexible polymers, examples of which are polyurethanes and silicones. Biocompatible materials may be used, especially for theouter layer1120 when theouter layer1120 has direct contact with body tissue. Alumen1128 may be included in aninner region1121, particularly for percutaneous leads1108, to allow a stylet to be inserted for purposes of pushing and steering the lead into the desired position within the patient. For leads where aninner region1121 is filled to define thelumen1128, such as where filars1124 are cables rather than the coils as shown, thisinner region1121 may be constructed of materials such as polyurethanes, silicones, polyetheretherketone (PEEK), nylon or other biocompatible polymer material.
• FIG. 2C shows a view of theimplantable lead1108 where various parameters related to the braid wires can be seen. The inner layer ofinsulation1122, as well as theouter layer1120, defines anaxial dimension1136 that runs along the length of thelead1108. Braid wires such asbraid wires1140,1142 are braided around theinner layer1122. A first set of braid wires includingbraid wire1140 is wound around theinner layer1122 in a first direction while a second set of braid wires includingbraid wire1142 is wound around theinner layer1122 in a second direction that is opposite the first. The braid wires of the first set and the braid wires of the second set weave together during the braiding with a braid wire of the first set passing over some wires and under others of the second set in a repeating pattern.
• The weaving may use a particular pattern, such as passing over one, passing under one, passing over one, and so on or such as passing over two, passing under two, passing over two, and so on. With wires of larger diameter, or where wires are used in pairs, then a pattern of two-over-two-under helps reduce the stress on the wire as it weaves back and forth. If the wires are small and single, with a relatively large aperture between braid wires, then one-over-one-under works well. The wire stress is a factor to consider because implant leads flex continually with body motion and typically arc expected to last many years.
• The braiding has various parameters of interest. A first parameter is thebraid angle1144. Here, thebraid angle1144 is defined as the angle of the braid wire as measured transversely from theaxial dimension1136; however, others sometimes define it relative to the axis of the lead. So, as shown inFIG. 2C, thebraid angle1144 is measured between the braid wire and thetransverse dimension1138. According to various embodiments, the braid angle measured in this way is less than 60 degrees.
• Thisbraid angle1144 has several implications. Thebraid angle1144 is one factor in setting the maximum dimension of thebraid aperture1141 shown inFIG. 2C, and hence the degree of coverage formed by the braid wires. Thisbraid angle1144 is also a factor in relation to the degree of stiffness of the lead in flexure and the tendency of the braid wires to break during flexure. The braid angle is also a factor in the cohesion of the outer layer ofinsulation1120 to the inner layer ofinsulation1122, because when the aperture is of adequate size, cohesion occurs between the twolayers1120,1122 through the aperture.
• Another parameter of interest as shown inFIG. 2C is theaxial spacing1146 between adjacent wires of a set. According to various embodiments, theaxial spacing1146 has an upper limit equal to thelead diameter1134. Theaxial spacing1146 is also a factor in the aperture size, the axial stiffness, the bending stiffness, and the kink resistance.
• Another parameter of interest, which is related to thebraid angle1144 and theaxial spacing1146, is the number of wires in each set. According to various embodiments, the first set of braid wires which are wound in the first direction includes at least three braid wires. Likewise, the second set of braid wires which are wound in the second direction includes at least three braid wires. These two sets of at least three braid wires each ensures that for the various ranges of parameters disclosed herein, theaperture1141 has a transverse dimension that is sufficiently small to effectively shield the RF energy in the MRI spectrum, which typically spans from 43 MHz to 128 MHz.
• The total number of braid wires is limited by the allowable axial and bend stiffness for the braid angle and braid wire size. In some examples, there may be as many as 16 braid wires in each set for a total of 32 braid wires. However, as shown in the example ofFIG. 2C, each set includes six braid wires, wherebraid wire1140 reappears on a given side of thelead1108 after five other braid wires are wound. Likewise,braid wire1142 reappears on the side of thelead1108 after five other braid wires are wound.
• FIG. 2D shows anotherlead embodiment1150 that demonstrates another braid wire parameter of interest. In this example, the braid wires are paired so that two braid wires that are in contact wind around theinner layer1122 instead of a single wire. For instance,dual braid wires1152 and1154 of a first set wound in a first direction are in contact as each winds around theinner layer1122.Dual braid wires1156 and1158 of a second set wound in a second direction are in contact as each winds around theinner layer1122.
• The braid wires bundled together in this manner affect the stiffness of thelead1108 as well as the aperture size. Bundling braid wires in this manner may provide coverage like that of wider dimensioned braid wires, such as rectangular braid wires, but without the increased bending stresses associated with the corners present on the rectangular braid wire.
• FIG. 2E is an enlarged view of a portion of a lead1108 to illustrate the cross-section of the braid wires. The view is a cross-section where the cut through thelead1108 is taken at an angle perpendicular to the direction of travel of thetopmost braid wire1142 so as to provide a true cross-section of thetopmost braid wire1142. Here thetopmost braid wire1142 has a round cross-section and provides abraid wire diameter1148. According to various embodiments, the braid wire diameter ranges from about 0.5 mils to about 2.5 mils. The braid wire diameter is measured as the dimension that faces outward from theinner layer1122 as shown inFIG. 2E. The round cross-section lacks corners that may otherwise affect the bend stiffness of thelead1108, but the round cross-section provides less coverage than other cross-sectional shapes that have a same height extending into theouter layer1120 from theinner layer1122.
• FIG. 2F is an enlarged view of a portion of a lead1160 to illustrate the cross-section of the braid wires. As inFIG. 2E, the view is a cross-section where the cut through thelead1160 is taken at an angle perpendicular to the direction of travel of thetopmost braid wire1162 so as to provide a true cross-section of thetopmost braid wire1162. Here thebraid wire1162 has a rectangular cross-section and provides abraid wire width1168. According to various embodiments, the braid wire width ranges from about 2 mils to about 5 mils. The braid wire width is measured as the dimension that faces outward from theinner layer1164 as shown inFIG. 2F. The rectangular cross-section has corners that may affect the bend stiffness of thelead1108 but provides more coverage than a round cross-sectional shape that has a same height extending into anouter layer1166 from theinner layer1164.
• FIG. 2G is an enlarged view of a portion of a lead1170 to illustrate the cross-section of the braid wires. As inFIG. 2E, the view is a cross-section where the cut through thelead1170 is taken at an angle perpendicular to the direction of travel of thetopmost braid wire1172 so as to provide a true cross-section of thetopmost braid wire1172. Here thetopmost braid wire1172 has an oval cross-section and provides a braid wiremajor axis diameter1178. According to various embodiments, the braid wire major axis diameter ranges from about 0.5 mils to about 4 mils. The braid wire major axis diameter is measured as the dimension that faces outward from theinner layer1176 as shown inFIG. 2G. The oval cross-section lacks corners that may affect the bend stiffness of thelead1108 but provides coverage similar to a rectangular cross-section that has a same height extending into anouter layer1174 from theinner layer1176.
• In each of the examples ofFIGS. 2E-2G, regardless of the cross-sectional shape and the material used, the braid wires have an ultimate tensile strength satisfactory for implantation. According to the various embodiments, this ultimate tensile strength is at least 150,000 pounds per square inch (150 ksi).
• FIG. 2H shows thelead1108 from end to end with theshield1118 in view to illustrate the termination of theshield1118 at theproximal end1105 and thedistal end1107. Theshield1118 terminates prior to reaching the mostdistal connector1109 of theproximal end1105 and prior to reaching the mostproximal electrode1116 of thedistal end1107. Terminating theshield1118 at adistance1117 from theconnector1109 and at adistance1119 from theelectrode1116 reduces the likelihood of RF energy that radiates from the end of the shield, leaking from the shield onto the conductor filars and then to theconnector1109 and/orelectrode1116. However, theshield termination distances1117,1119 are not too large so that adequate coverage over thefilars1124 is maintained.
• The shield termination distance from the distal electrodes and proximal connectors may vary. According to the various embodiments, the distance may range from about 0.5 millimeters to about 10 centimeters depending upon the location of thelead1108. For instance, if the distal tip is located in the brain or spinal column where intensities of RF energy are lower, then distance from the end of theshield1118 to the nearest edge of the distal electrode may be from 0.5 mm up to about 10 cm, or from about 2 mm to 2 cm to further reduce electrode coupling and filar exposure. However, in other locations where theentire lead1108 is just under the skin as for peripheral nerve stimulation, the distance from the end of theshield1118 to the nearest edge of the distal electrode may be less than about 2 cm to prevent overexposure of thefilars1124. In these cases, the distance may be on the order of 2 mm or more to ensure that excessive RF coupling from theshield1118 to the electrodes is avoided.
• In one particular example, thelead1108 is provided with ashield1118 where the total lead diameter is 53.6 mils. Theinner insulation layer1122 has an as assembled inside diameter of 35 mils and an as assembled outside diameter of 50.19 mils for a total thickness of 5.89 mils or 5.39 mils to the inner edge of the braid wire. Theoutside insulation layer1120 has an as assembled outside diameter of 53.6 mils and a total thickness of 3.41 mils, with 1.41 mils of thickness existing over braid wire intersection points and while the thickness over a single braid wire approaches 2.66 mils as the single braid wires approaches an intersection point where the single braid wire will pass under an intersecting braid wire. The braid wire is round in cross-section with a diameter of 1.25 mils and being embedded by about 0.5 mils into theinner layer1122. Two sets of eight braid wires are provided for a total of sixteen braid wires, with the braid wires establishing a braid angle of 22 degrees with an axial spacing between adjacent braid wires of 7.5 mils. Theshield1118 terminates about 2 mm from the nearest edge of the distal electrode and proximal connector. In another particular example, the lead108 is provided with the specifications described in the preceding paragraph except that the shield gaps and depth the shield sinks into theinner insulation layer1122 are different. Here, theshield1118 terminates about 1 mm from the nearest edge of the distal electrode and proximal connector and the shield sinks 0.25 mil. As a result, the inner insulation thickness to the inner edge of the braid wire is 5.6 mils.
• In another particular example, the lead108 is provided with the specifications described in the preceding paragraph except insulation thicknesses, braid angle, and proximal shield gaps differ. In this example, the braid depth from the outer surface of theouter layer1120 to the outer edge of a braid wire is about 2 mils at braid wire intersection points while the thickness over the braid wire approaches 3.25 mils as the single braid wire approaches an intersection point where the braid wire passes under an intersecting braid wire. The inner insulation layer122 has an average thickness of 4.5 mils to the inner edge of the braid wire while the braid wire sinks into theinner insulation layer1122 by about 0.25 mil. Theshield1118 terminates about 1.27 mm from the nearest edge of the distal electrode and terminates about 10 mm from the nearest edge of the proximal connector. The braid angle is about 23 degrees.
• Embodiments disclosed in relation toFIGS. 3-10C provide for radio frequency (RF) grounding of a shield present within an implantable lead. The shield may be grounded in various ways such as to a can of an implantable medical device (IMD) or to a ground plate on a header of the IMD. The pathway for grounding may be a direct current pathway or be capacitively coupled. The pathway for grounding the shield may couple to the shield at a point along the lead that is external to the header of the IMD or may couple to the shield at a point within the header.
• FIG. 3 shows an example of an implantablemedical system2100 that includes anIMD2102 coupled to alead2108. TheIMD2102 includes ametal can2104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD2102 includes aheader2106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can2104. Theheader2106 is shown transparently for purposes of illustration. Theheader2106 provides a structure for securing thelead2108 to theIMD2102 and for establishing electrical connectivity between circuitry of theIMD2102 and electrodes of thelead2108.
• Thelead2108 includeselectrodes2116 on a proximal end that are positioned at a stimulation site within a patient. The lead also includes connector rings2110 on a proximal end that is positioned within theheader2106. Theconnectors2110 make physical contact withelectrical connections2111 within the header. Theelectrical connections2111 may include a metal contact that theelectrode2110 rests against upon being inserted into theheader2106 where a wire extends from the metal contact into thecan2104 where the circuitry is housed. Signals applied by theIMD2102 to theelectrodes2110 are conducted through thelead2108 to theelectrodes2116 to provide the stimulation therapy to the patient.
• Thelead2108 is secured in theheader2106 such as by aset screw block2112 within theheader2106 that allows at least oneset screw2114 to be tightened against at least one of theconnectors2110. Theshield2118 may be grounded by metal contacts provided along the lead to establish a ground pathway from theshield2118 to the tissue. As another option, theshield2118 may be located within thelead2108 at a small distance from the surface so that theshield2118 will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length.
• FIGS. 4A and 4B show an example of thelead2108, where ashield2118 is present. Anouter jacket layer2120 is shown transparently inFIG. 4A for purposes of illustrating theshield2118. Theshield2118 blocks at least some RF energy from directly coupling toconductive filars2124 that are present within thelead2108. Theconductive filars2124 extend the length of the lead and interconnect theproximal connectors2110 to thedistal electrodes2116 so that stimulation signals are conducted from the proximal end to the distal end of thelead2108.
• As shown inFIG. 4A, theshield2118 of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield2118, particularly for embodiments where a portion of theshield2118 may be exposed for purposes of grounding. While theshield2118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead2108 in an overlapping manner or anouter layer2120 that is heavily doped with conductive particles.
• As shown inFIG. 4B, theshield2118 may be embedded within the jacket of thelead2108. One manner of constructing thelead2108 with theshield2118 is to provide aninner jacket2122 that encloses thefilars2124 and anyadditional insulation layer2126, such as polytetrafluoroethylene (PTFE) that may surround each filar2124. Theshield2118 may then reside on the outer portion of theinner jacket2122, and theouter jacket2120 may then enclose theshield2118. Theouter jacket2120 maybe added over thebraid2118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield2118 to RF couple to tissue, typically as a capacitive coupling, either as an alternative to grounding at the can of the IMD or in addition to grounding at the can, the amount of theouter jacket layer2120 covering theshield2118 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield2118 grounds at the can of the IMD and grounding via a capacitive coupling from the shield through theouter jacket2120 directly to the tissue is of less significance, then theshield2118 may be located further from the outer surface of thelead2108.
• The inner andouter jackets2122,2120 may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes, and silicones. Alumen2128 may be present inside of theinner jacket2122 around which theinsulated filars2124 are coiled or otherwise positioned. Thelumen2128 may be useful, particularly for percutaneous leads2108, to allow a stylet to be inserted for purposes of pushing and steering thelead2108 into the desired position within the patient.
• FIG. 4C shows one example of exposing theshield2118 for purposes of grounding theshield2118. In this example, theouter layer2120 of the jacket has been removed at first point along thelead2108 near the proximal end to expose theshield2118 and theinner jacket2122. For example, an excimer laser may be used to ablate theouter layer2120. Physical contact may then be established between theshield2118 and an electrode attached to the lead, a spring loaded connector or a connector block, a wire, or other direct current or capacitive coupling. For instance, a ground wire could be adhesively bonded with glue or tape in contact with the exposedshield2118. Depending upon the embodiment, this first point along the lead where theshield2118 is exposed may be located either inside or outside of the header of the IMD. Furthermore, depending upon the embodiment the coupling to the exposedshield2118 may be a direct current coupling or a capacitive coupling, either providing a pathway for RF current to pass to ground.
• FIG. 4D shows another example of providing a pathway to ground theshield2118. Here, anelectrode2130 is attached at the first point along thelead2108 near the proximal end to provide a robust physical connection to a spring loaded connector, a connector block, a wire, or other direct current or capacitive coupling. Depending upon the embodiment, this first point along the lead where theelectrode2130 is positioned may be located either inside or outside of the header of the IMD. Furthermore, depending upon the embodiment a coupling to theelectrode2130 may be a direct current coupling or a capacitive coupling, either providing a pathway for RF current to pass to ground.
• FIGS. 5A-5C show embodiments of grounding the shield to the can of the IMD by using a connector block mounted on the IMD and coupling a grounding path to the shield outside of a header of the IMD. The implantablemedical system2150 includes anIMD2152 having a metal can2154 and aheader2156. One ormore leads2164 extend from the header and pass through aconnector block2158 that is mounted to thecan2154.
• Theconnector block2158 includes features to ground the shield of thelead2164 to thecan2154, such as aconnector2160 and acan attachment2162. For instance, theconnector block2158 may be constructed of a biocompatible plastic or other non-conductor while theconnector2160 provides conduction to thecan attachment2162. Thecan attachment2162 may be of various forms. For example, a wire that extends from theconnector2160 to thecan2154 where thecan attachment2162 is welded or otherwise affixed to thecan2154. As another example, theconnector block2158 may include a metal plate that contacts the metal can2154 via a weld or other attachment.
• FIG. 5B is a side view showing a pair of pass-through features of theconnector block2158 and a pair ofleads2164 having shields to be grounded. Theconnector block2158 is shown in a cross-section so that aset screw2168 is visible. The electrode or other contact for the shield of thelead2164 is positioned within the pass-through2166 such that theset screw2168 and the electrode or other contact for the shield are aligned. Theset screw2168 is tightened against the electrode or other contact to establish the ground to thecan2154. The pass-through2166 may be a slot through theconnector block2158 so that thelead2164 can be lowered into the slot. As another option, the pass-through2166 may be a bore through theconnector block2158 and thelead2164 is fed through the bore.
• FIG. 5C is a side view showing a pair of pass-through features of another embodiment of theconnector block2158 and a pair ofleads2164 having shields to be grounded. Theconnector block2158 includes spring loadedconnectors2172. The electrode or other contact for the shield of thelead2164 is positioned within the pass-through2170 such that the spring loadedconnector2172 and the electrode or other contact for the shield are aligned. The electrode or other contact to the shield is forced within the spring loadedconnector2172 to establish the ground to thecan2154. As with the embodiment ofFIG. 5B, the pass-through2170 of this embodiment may be a slot through theconnector block2158 so that thelead2164 can be lowered into the slot or may be a bore through theconnector block2158 where thelead2164 is fed through the bore.
• FIG. 6 shows one example of a spring loadedconnector2174. The spring loadedconnector2174 can open slightly when forced by insertion of thelead2164 and then is biased back against the electrode or other contact of thelead2164 once the lead is seated within the spring loadedconnector2174. Other spring loaded connector designs are also applicable.
• FIG. 7A shows an implantablemedical system2180 where the shield of alead2188 is being grounded to a metal can2184 of anIMD2182 externally of theheader2186. Here, a direct current pathway is being provided between the shield and the metal can2184. A spring loadedconnector2192 contacts anelectrode2190 on thelead2188 where theelectrode2190 is in contact with the shield. Awire2194 may be made from materials such as titanium, tantalum, platinum, stainless steel, nickel chromium, and alloys, and serves as a ground conductor. Thiswire2194 is attached to the spring loadedconnector2192 by a weld or other bond. Thewire2194 extends from the spring loadedconnector2192 to the metal can2184 where aweld2196 or other bond such as with glue or tape attaches thewire2194 to the metal can2184.
• FIG. 7B shows an implantablemedical system2200 where the shield of alead2208 is being grounded to a metal can2204 of anIMD2202 externally of theheader2206. Here, a direct current pathway is also being provided between the shield and the metal can2204. Ametal connector block2210 having aset screw2212 contacts an electrode on thelead2208 where the electrode is in contact with the shield. Awire2214 serving as a ground conductor is attached to theconnector block2210 by a weld or other bond. Thewire2214 extends from theconnector block2212 to the metal can2204 whereglue2216, such as a conductive epoxy or carbon filled polymer adhesive, or other bond such as a weld or tape attaches thewire2214 to the metal can2204.
• FIG. 7C shows an implantablemedical system2220 where the shield of alead2228 is being grounded to a metal can2224 of anIMD2222 externally of theheader2226. Here, a direct current pathway is also being provided between the shield and the metal can2224. Acoupling2230 such as a ring electrode is in contact with the shield. Awire2232 serving as a ground conductor is attached to thecoupling2230 by a weld or other bond. Thewire2232 extends from thecoupling2230 to the metal can2224 where acrimp connector2234 or other bond such as a weld or tape attaches thewire2232 to the metal can2224.
• For the examples ofFIGS. 7A-7C, various examples of connecting the grounding wire to the lead and to the can are disclosed. It will be appreciated that any combination of these and other examples of connections of the ground wire may be used to provide the direct current pathway that ultimately provides an RF ground from the shield to the metal can.
• FIG. 8A shows an implantablemedical system2240 where the shield of alead2248 is being grounded to a metal can2244 of anIMD2242 externally of theheader2246. Here, a capacitively coupled pathway is being provided between the shield and the metal can2244. Acoupling2250 such as a spring loaded connector or a ring electrode contacts thelead2248 and is in contact with the shield. Awire2252 serving as a ground conductor is attached to thecoupling2250 by a weld or other bond. Thewire2252 extends from thecoupling2250 to nearby the metal can2244 where a piece oftape2254 or other tab affixed to thecan2244 attaches to thewire2252. Thetape2254, such as double-sided tapes, epoxies, or polymer based adhesive, or other tab holds the wire in proximity to the metal can2244 to establish a capacitive coupling between thewire2252 and thecan2244.
• FIG. 8B shows an implantablemedical system2260 where the shield of alead2268 is being grounded to a metal can2264 of anIMD2262 externally of theheader2266. Here, a capacitively coupled pathway is being provided between the shield and the metal can2264. A piece oftape2270 or other tab contacts thelead2268 at a point where the shield is present. Awire2272 serving as a ground conductor is attached to thetab2270 and is held nearby thelead2268 and shield to establish a capacitive coupling between thewire2272 and the shield. Thewire2272 extends from thetab2270 to the metal can2264 and is affixed to the metal can2264 with aweld2274 or other bond.
• FIG. 8C shows an implantablemedical system2280 where the shield of alead2288 is being grounded to a metal can2284 of anIMD2282 externally of theheader2286. Here, a capacitively coupled pathway is being provided between the shield and the metal can2284. Acoupling2290 such as a spring loaded connector or a ring electrode contacts thelead2288 and is in contact with the shield. Awire2292 serving as a ground conductor is attached to thecoupling2290 by a weld or other bond and extends from thecoupling2290 to nearby the metal can2284. Non-conductive glue or anothernon-conductive bond2294 to thecan2284 is present to adhere to thewire2292 and hold the wire in proximity to the metal can2284 to establish a capacitive coupling between thewire2292 and thecan2284.
• For the examples ofFIGS. 8A-8C, various examples of connecting the grounding wire to the lead and to the can are disclosed, using combinations of direct current couplings and capacitive couplings. It will be appreciated that any combination of these and other examples of direct current coupling and capacitive coupling connections of the ground wire may be used to provide the capacitively coupled pathway that ultimately provides an RF ground from the shield to the metal can.
• FIG. 9A shows an implantablemedical system2300 where the shield of alead2308 is being grounded to a metal can2304 of anIMD2302 within theheader2306.Proximal electrodes2310 of thelead2308 are electrically connected viawires2312 to theIMD2302. Here, a direct current coupled pathway is being provided between the shield and the metal can2304. Acoupling2314 such as a spring loaded connector or a ring electrode contacts thelead2308 and is in contact with the shield. Aset screw2316 may be present to further hold the proximal end of thelead2308 in place within theheader2306. Awire2318 serving as a ground conductor is attached to thecoupling2314 by a weld or other bond and extends from thecoupling2314 to the metal can2304 where aweld2320 or other bond holds thewire2318 to thecan2304.
• FIG. 9B shows an implantablemedical system2330 where the shield of alead2338 is being grounded to a metal can2334 of anIMD2332 within theheader2336.Proximal electrodes2340 of thelead2338 are electrically connected viawires2342 to theIMD2302. Here, a direct current coupled pathway is being provided between the shield and the metal can2334. Acoupling2344 such as a spring loaded connector or a ring electrode contacts thelead2338 and is in contact with the shield. Awire2346 serving as a ground conductor is attached to thecoupling2344 by a weld or other bond and extends from thecoupling2344 to the metal can2334 where aweld2348 or other bond holds thewire2346 to thecan2334.
• FIG. 9C shows an implantablemedical system2350 where the shield of alead2358 is being grounded to a metal can2354 of anIMD2352 within theheader2356.Proximal electrodes2360 of thelead2358 are electrically connected viawires2362 to theIMD2352. Here, a capacitively coupled pathway is being provided between the shield and the metal can2354. Acoupling2364 such as a spring loaded connector or a ring electrode contacts thelead2358 and is in contact with the shield. A wire2366 serving as a ground conductor is capacitively coupled to thecoupling2364 within theheader2356 by the header structure holding the wire in proximity to thecoupling2364. The wire2366 extends from the capacitive coupling to the metal can2354 where aweld2368 or other bond holds the wire2366 to thecan2354.
• FIG. 9D shows an implantablemedical system2370 where the shield of alead2378 is being grounded to a metal can2374 of anIMD2372 within theheader2376.Proximal electrodes2380 of thelead2378 are electrically connected viawires2382 to theIMD2372. Here, a capacitively coupled pathway is being provided between the shield and the metal can2374. Acoupling2384 such as a spring loaded connector or a ring electrode contacts thelead2378 and is in contact with the shield. Awire2386 serving as a ground conductor is capacitively coupled to thecoupling2384 within theheader2376 by the header structure holding the wire in proximity to thecoupling2384. Thewire2386 extends from the capacitive coupling toward the metal can2374 and is capacitively coupled to thecan2374 within theheader2376 by the header structure holding the wire in proximity to thecan2374.
• FIG. 9E shows an implantablemedical system2390 where the shield of alead2398 is being grounded to a metal can2394 of anIMD2392 within theheader2396.Proximal electrodes2402 of thelead2398 are electrically connected viawires2404 to theIMD2392. Here, a capacitively coupled pathway is being provided between the shield and the metal can2394. Acoupling2406 such as a spring loaded connector or a ring electrode contacts thelead2398 and is in contact with the shield. A shunt plate such as atab2408 or similar structure serving as a ground conductor extends from thecoupling2406 toward thecan2394 and is capacitively coupled to thecan2394 within theheader2396 by the header structure holding thetab2408 in proximity to thecan2394.
• FIG. 9F shows an implantablemedical system2410 where the shield of alead2418 is being grounded to a metal can2414 of anIMD2412 within theheader2416.Proximal electrodes2420 of thelead2418 are electrically connected viawires2422 to theIMD2412. Within thecan2414, filter feed through (FFT)circuits2424 are present to capacitively couple thewires2422 to the metal can2414 while allowing connection of thewires2422 to stimulation circuits. TheFFT circuits2424 for theelectrodes2420 protects theIMD2412 from electromagnetic background noise picked up by the filars, albeit potentially less noise due to the presence of the shield.
• Here, a capacitively coupled pathway is being provided between the shield and the metal can2414 also via anFFT circuit2430. Acoupling2426 such as a spring loaded connector or a ring electrode contacts thelead2418 and is in contact with the shield. A wire2428 serving as a ground conductor extends from thecoupling2426 toward thecan2414 and terminates at theFFT circuit2430 to provide the capacitive coupling between the shield and thecan2414.
• As shown, thecoupling2426 to the shield may be an existing electrode of thelead2418 that provides stimulation signals to a filar within thelead2418. In that case, theFFT circuit2430 may provide capacitive coupling to the can for both the filar and the shield. In such a case, it may be desirable to capacitively couple the shield to thecoupling2426 so that relatively low frequency stimulation signals arc not present on the shield but induced RF current on the shield has a pathway to theFFT circuit2430. For example, the outer jacket may separate the shield from the electrode by a separation on the order of 0.5-5 mils to allow an RF coupling to occur. As an alternative to using the same coupling and FFT circuit for both the shield and the filar, the shield may be provided adedicated coupling2426 and adedicated FFT circuit2430 that are independent of any electrodes and filars within thelead2418.
• For the examples ofFIGS. 9A-9F, various examples of connecting the grounding conductor to the lead and to the can within the header are disclosed, using combinations of direct current couplings and capacitive couplings. It will be appreciated that any combination of these and other examples of direct current coupling and capacitive coupling connections of the ground conductor may be used to provide the capacitively coupled pathway that ultimately provides an RF ground from the shield within the header to the metal can. For instance, a capacitive coupling may be provided in any of the various embodiments at the coupling to the shield as discussed above in relation toFIG. 9F.
• FIG. 10A shows an implantablemedical system2440 where the shield of alead2448 is being grounded to a metal can2444 of anIMD2442 outside of theheader2446. Here, a ground pathway is being provided between the shield and aground plate2454 installed on theheader2446. The ground plate provides a relatively large surface area in comparison to an individual electrode and allows for safe dissipation of induced RF current on the shield in the same manner as grounding to thecan2444. Acoupling2450 such as a spring loaded connector or a ring electrode contacts thelead2448 and is in contact with the shield. Awire2452 that serves as a ground conductor is attached to thecoupling2450 by a weld or other bond and extends from thecoupling2450 to theground plate2454 where a weld or other bond holds thewire2452 to theground plate2454.
• FIG. 10B shows an implantablemedical system2460 where the shield of alead2468 is being grounded to a metal can2464 of anIMD2462 within theheader2466. Here, a ground pathway is also being provided between the shield and aground plate2474 installed on theheader2466. Acoupling2470 such as a spring loaded connector or a ring electrode contacts thelead2468 and is in contact with the shield. Awire2472 that serves as a ground conductor is attached to thecoupling2470 by a weld or other bond and extends from thecoupling2470 to theground plate2474 where a weld or other bond holds thewire2472 to theground plate2474.
• FIG. 10C shows an implantablemedical system2480 where the shield of alead2488 is being grounded to a metal can2484 of anIMD2482 within theheader2486. Here, a ground pathway is being provided between the shield and aconnector block2492 with a relatively large surface area that also acts as a ground plate installed on theheader2486. In this example, theconnector block2492 is a set screw block that uses aset screw2494 to tighten against acoupling2490 on thelead2488. Thecoupling2490 such as a ring electrode contacts thelead2448 and is in contact with the shield. Aset screw2494 extends from thecoupling2490 and through theconnector block2492 and acts as a ground conductor to provide the ground pathway from the shield to theconnector block2492. Other conductive features may also be present within theconnector block2492 to contact thecoupling2490 and provide the RF ground pathway.
• For the examples ofFIGS. 10A-10C, various examples of connecting the grounding conductor to the lead and to the ground plate arc disclosed. It will be appreciated that any combination of direct current coupling and capacitive coupling connections may be used to provide the pathway that ultimately provides an RF ground from the shield to the ground plate. For instance, a capacitive coupling may be provided in any of the various embodiments at the coupling to the shield as shown inFIGS. 10A-10C and as discussed above in relation toFIG. 9F. Likewise, a capacitive coupling may be present between a ground conductor extending from the coupling to the shield and the ground plate.
• Embodiments disclosed in relation toFIGS. 11-15E also provide for radio frequency (RF) grounding of a shield present within an implantable lead. The shield may be grounded in various ways such as directly to tissue at one or more points along the lead body. The pathway for grounding may be a direct current pathway or be capacitively coupled. The pathway for grounding may utilize an exposed or nearly exposed shield at one or more points along the lead body, metal conductors attached to the lead at one or more points, a jacket with a conductive doping at one more points, and so forth.
• FIG. 11 shows an example of an implantablemedical system3100 that includes anIMD3102 coupled to alead3108. TheIMD3102 includes ametal can3104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD3102 includes aheader3106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can3104. Theheader3106 is shown transparently for purposes of illustration. Theheader3106 provides a structure for securing thelead3108 to theIMD3102 and for establishing electrical connectivity between circuitry of theIMD3102 and electrodes of thelead3108.
• Thelead3108 includeselectrodes3116 on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings3110 on a proximal end that is positioned within theheader3106. The connector rings3110 make physical contact withelectrical connections3111 within the header. Theelectrical connections3111 may include a metal contact that theconnector ring3110 rests against upon being inserted into theheader3106 where a wire extends from the metal contact into thecan3104 where the circuitry is housed. Signals applied by theIMD3102 to the connector rings3110 are conducted through thelead3108 to theelectrodes3116 to provide the stimulation therapy to the patient.
• Thelead3108 is secured in theheader3106 such as by aset screw block3112 within theheader3106 that allows at least oneset screw3114 to be tightened against at least one of theelectrodes3110. With thelead3108 in place, theshield3118 of thelead3108 may then become grounded to the body along one or more points down the length of the lead from theIMD3102.
• FIGS. 12A and 12B show an example of thelead3108, where ashield3118 is present. Anouter jacket layer3120 is shown transparently inFIG. 12A for purposes of illustrating theshield3118. Theshield3118 blocks at least some RF energy from directly coupling toconductive filars3124 that are present within thelead3108. Theconductive filars3124 extend the length of the lead and interconnect theproximal electrodes3110 to thedistal electrodes3116 so that stimulation signals are conducted from the proximal end to the distal end of thelead3108.
• As shown inFIG. 12A, theshield3118 of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield3118, particularly for embodiments where a portion of theshield3118 may be exposed for purposes of grounding. While theshield3118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead3108 in an overlapping manner or anouter layer3120 that is heavily doped with conductive particles.
• As shown inFIG. 12B, theshield3118 may be embedded within the jacket of thelead3108. One manner of constructing thelead3108 with theshield3118 is to provide aninner jacket3122 that encloses thefilars3124 and anyadditional insulation layer3126, such as polytetrafluoroethylene (PTFE) that may surround each filar3124. Theshield3118 may then reside on the outer portion of theinner jacket3122, and theouter jacket3120 may then enclose theshield3118. Theouter jacket3120 maybe added over thebraid3118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield3118 to RF couple to tissue, typically as capacitive coupling, either as an alternative to grounding at the can of the IMD or in addition to grounding at the can, the amount of theouter jacket layer3120 covering theshield3118 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield3118 grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, the shield may be located further from the outer surface of thelead3108 with additional features of the lead providing the coupling at the one or more specific locations as discussed below.
• The inner andouter jackets3122,3120 may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes, and silicones. Alumen3128 may be included inside of theinner jacket3122 around which theinsulated filars3124 are coiled or otherwise positioned. Thelumen3128 may be useful, particularly for percutaneous leads3108, to allow a stylet to be inserted for purposes of pushing and steering thelead3108 into the desired position within the patient.
• FIG. 12C shows one example of exposing theshield3118 at a particular point along thelead3108 for purposes of grounding theshield3118. In this example, theouter layer3120 of the jacket has been removed at a first point along thelead3108 distant from the distal end to expose theshield3118 and theinner jacket3122. For example, an excimer laser may be used to ablate theouter layer3120. Physical contact may then be established between theshield3118 and the tissue or between theshield3118 and an electrode attached to the lead.
• FIG. 12D shows another example of providing a pathway to ground theshield3118. Here, a metal conductor, specifically aring electrode3130, is attached at the first point along thelead3108 distant from the distal end to provide a robust physical connection to the tissue while avoiding tissue in-growth that may occur if theshield3118 is exposed directly. Depending upon the embodiment, a coupling of theshield3118 to theelectrode3130 may be a direct current coupling or a capacitive coupling, either providing a pathway for RF current to pass to ground. Thering electrode3130 may be attached by methods such as crimping, clamping, welding, and the like.
• FIG. 12E shows an example of nearly exposing theshield3118 at a particular point along thelead3108 for purposes of grounding theshield3118. In this example, theouter layer3120 of the jacket has been almost entirely removed at a first point along thelead3108 distant from the distal end to nearly expose theshield3118 and theinner jacket3122. Only a verythin layer3120′, on the order of about 0.5-5 mils, of theouter layer3120 is remaining Physical contact between theshield3118 and the tissue is avoided so that tissue in-growth does not occur, and theshield3118 capacitively couples to the tissue to provide the RF pathway to ground.
• FIG. 12F shows an example of exposing, or nearly exposing, theshield3118 at a plurality ofpoints3202 along the lead. At thesepoints3202, theouter layer3120 has been at least partially ablated or otherwise removed to place theshield3118 in closer proximity to the body tissue so that an RF pathway to ground is established. Where theshield3118 is exposed, the RF pathway is a direct current coupling to the tissue. Where theshield3118 is nearly exposed, the RF pathway is a capacitive coupling to the tissue.
• Where multiple points of the RF pathway to ground are present, a particular separation of the multiple points is provided. A nearest edge-to-nearest edge distance between one point and an adjacent one is shown by the distance fromedge3204 toedge3206. Where the outer layer is removed, the flexibility and strength of the lead is altered for the region including those points and this distance fromedge3204 to edge3206 can be used to control the flexibility and strength.
• Where multiple points of the RF pathway to ground are direct current couplings, another concern is current induced by the gradient magnetic fields present in a magnetic resonance (MR) scan. If the most proximal and most distal points of the direct current coupling are spaced too far apart, then the magnetic gradient may induce a dangerous current through the shield and produce a significant stimulation of tissue at those ground points along the lead. Therefore, choosing the nearest edge-to-nearest edge separation to fall within an illustrative range of 2 millimeters (mm) or more with a most proximal to most distal separation, such asedge3204 to edge3208, of about 40 centimeters (cm) or less may allow for flexibility of the lead in the region while maintaining small loops that prevent large magnetic gradient induced currents should the shield be exposed at thepoints3202.
• FIG. 12G shows an example of coupling theshield3118 to ground with a plurality of metal conductors such asrings3130 at a plurality ofpoints3210 along the lead. At thesepoints3202, theouter layer3120 has been at least partially ablated or otherwise removed to place theshield3118 in close proximity with themetal conductors3130 so that an RF pathway to ground is established through themetal conductors3130. Where theshield3118 is exposed to themetal conductors3130, the RF pathway is a direct current coupling to the tissue. Where theshield3118 is nearly exposed to themetal conductors3130, the RF pathway is a capacitive coupling to the tissue.
• As with the example ofFIG. 12F, where multiple points of the RF pathway to ground are present, a particular separation of the multiple points is provided. A nearest edge-to-nearest edge distance between one point and an adjacent one is shown by the distance fromedge3212 toedge3214. The flexibility and strength of the lead is altered for the region including those points, with themetal conductors3130 limiting the bending in this region to essentially those sections of lead between themetal conductors3130. Thus, in one example, a nearest edge-to-nearest edge distance may be maintained at or above 2 mm or 50% of the grounding ring length so that flexibility of the lead is maintained.
• Also, where theshield3118 is direct current coupled to themetal conductors3130, a magnetic gradient induced current is of concern because themetal conductors3130 have a direct current coupling to the tissue. In that case, the separation of the most proximal to the most distal may be kept within a range that prevents a large loop and avoids a large magnetic induced gradient current. In this particular example, the most proximal to the most distal distance, such as fromedge3212 to edge3216, may be maintained at or below approximately 40 cm so that magnetic gradient induced currents are insignificant.
• FIG. 12H shows a cross-section of thelead3108 at a particular point where theouter jacket3120 has been ablated or otherwise removed. In this example, thelead3108 at this particular point includes ametal conductor3130 with a direct current coupling to theshield3118. Theouter layer3120 of the jacket has been removed to allow themetal conductor3130, a ground ring as shown, to wrap around the lead and contact theshield3118. The filars may be present within theinner jacket3122 or any other inner layer as shown or within the lumen created by the inside wall of theinner jacket3122 or any other inner layer as shown inFIG. 12B.
• FIG. 12I shows a cross-section of thelead3108 at a particular point where theouter jacket3120 has been ablated or otherwise removed. In this example, thelead3108 at this particular point has theshield3118 exposed to tissue for a direct current coupling by entirely removing theouter layer3120. The filars may be present within theinner jacket3122 or any other inner layer as shown or within the lumen created by the inside wall of theinner jacket3122 or any other inner layer as shown inFIG. 12B.
• FIG. 12J shows a cross-section of thelead3108 at a particular point where a portion of theouter jacket3120 has been ablated or otherwise removed. In this example, thelead3108 at this particular point includes ametal conductor3130 with a capacitive coupling to theshield3118. Theouter layer3120 of the jacket has been partially removed, with a remaining thickness of about 0.5 mils to 5 mils, to nearly expose theshield3118. This allows themetal conductor3130, a ground ring as shown, to wrap around the lead and capacitively couple with theshield3118 at RF frequencies. The filars may be present within theinner jacket3122 or any other inner layer as shown or within the lumen created by the inside wall of theinner jacket3122 or any other inner layer as shown inFIG. 12B.
• FIG. 12K shows a cross-section of thelead3108 at a particular point where a portion of theouter jacket3120 has been ablated or otherwise removed. Theouter layer3120 of the jacket has been partially removed, with a remaining thickness of about 0.5 mils to 5 mils, to nearly expose theshield3118. Theshield3118 capacitively couples to the tissue at RF frequencies. The filars may be present within theinner jacket3122 or any other inner layer as shown or within the lumen created by the inside wall of theinner jacket3122 or any other inner layer as shown inFIG. 12B.
• FIG. 13A shows an example of aring electrode3220 that may be attached to alead3108 to form the RF pathway to ground from theshield3118. The ring electrode may be constructed of platinum, platinum-iridium, titanium, tantalum, stainless steel, and other similar biocompatible metals. Thering electrode3220 may have agap3222. Thering electrode3220 may be sprung open to fit around the lead at the particular point where the jacket has been ablated, and thering electrode3220 is crimped back into a tightly fitting configuration. As another example, thering electrode3220 may be flat and then rolled into the ring shape about the lead. In some examples, thegap3222 may close upon crimping while in other embodiments thegap3222 may remain to some degree.
• FIG. 13B shows an example of anotherring electrode3224 that may be attached to alead3108 to form the RF pathway to ground from theshield3118. Thering electrode3224 includes atab3226 that extends away from the lead to provide an additional surface area and extension into the tissue for adding grounding of theshield3118. Thering electrode3220 may be sprung open to fit around the lead at the particular point where the jacket has been ablated and thering electrode3220 is crimped back into a tightly fitting configuration. As in the previous example, thering electrode3224 may be flat and then rolled into the ring shape about the lead while maintaining a flat portion as thetab3226.
• FIG. 13C shows an example of anotherring electrode3228 that may be attached to alead3108 to form the RF pathway to ground from theshield3118. Thering electrode3228 forms a helix. Thering electrode3228 may be sprung open to fit around the lead at the particular point where the jacket has been ablated and thering electrode3228 is crimped back into a tightly fitting helical configuration. As in the previous examples, thering electrode3228 may be flat and then rolled into the helical ring shape about the lead.
• FIG. 13D shows an example of aring electrode3230 that may be attached to alead3108 to form the RF pathway to ground from theshield3118. Thering electrode3230 has anouter side3234 that faces away from theshield3118 and aninner side3236 that faces toward theshield3118 and may directly contact theshield3118. In this example, theouter side3234 has anon-conductive coating3232 applied so that theouter side3234 does not have a direct coupling to the tissue. The non-conductive coating may be of various types such as polyurethane, silicone or other biocompatible polymers.
• Theinner side3236 may either have a direct current coupling or a capacitive coupling to the shield. Withmultiple ring electrodes3230 in place on a lead, magnetic gradient induced current which is at a relatively low frequency is not a concern because thenon-conductive coating3232 prevents the relatively low frequency induced current from flowing to the tissue. Thus, the distance between adjacent electrodes is not limited by induced current concerns. Meanwhile, the high frequency RF induced current does ground to the tissue through the capacitive coupling provided by thenon-conductive coating3232.
• FIG. 13E shows an example of aring electrode3240 that may be attached to alead3108 to form the RF pathway to ground from theshield3118. Thering electrode3240 has anouter side3242 that faces away from theshield3118 and aninner side3244 that faces toward theshield3118 and may directly contact theshield3118. In this example, theinner side3244 has anon-conductive coating3246 applied so that theinner side3244 does not have a direct coupling to theshield3118 even if theshield3118 is entirely exposed to thering electrode3240. Thenon-conductive coating3246 may be of the various types discussed above in the previous example.
• Theouter side3242 may have a direct current coupling to the tissue. Withmultiple ring electrodes3240 in place on a lead, magnetic gradient induced current is not a concern because the non-conductive coating prevents the relatively low frequency induced current from flowing from theshield3118 to thering electrode3240. Thus, the distance between adjacent electrodes is not limited by induced current concerns. Meanwhile, the high frequency RF induced current does ground through thering electrode3240 to the tissue through the capacitive coupling provided by thenon-conductive coating3246.
• FIG. 13F shows an example of aring electrode3250 that may be attached to alead3108 to form the RF pathway to ground from theshield3118. Thering electrode3250 has anouter side3252 that faces away from theshield3118 and may directly contact the tissue and aninner side3254 that faces toward theshield3118 and may directly contact theshield3118. In this example, both theinner side3254 and theouter side3252 have anon-conductive coating3256 applied. Theinner side3254 does not have a direct current coupling to theshield3118 even if the shield is entirely exposed to thering electrode3250. Theouter side3252 does not have a direct current coupling to the tissue even if in physical contact with the tissue. Thenon-conductive coating3256 may be of the various types discussed above in the previous examples.
• Withmultiple ring electrodes3250 in place on a lead, magnetic gradient induced current is not a concern because the non-conductive coating prevents the relatively low frequency induced current from flowing from theshield3118 to thering electrode3250. Thus, the distance between adjacent electrodes is not limited by induced current concerns. Meanwhile, the high frequency RF induced current does ground through thering electrode3250 to the tissue through the capacitive couplings on each side of thering electrode3250 provided by thenon-conductive coating3256.
• While the examples ofFIGS. 13A-13F show various shapes of ring electrodes, it will be appreciated that various other shapes are also applicable for metal conductors being attached to the lead to provide the RF ground pathway. Furthermore, whileFIGS. 13D-13F show a particular ring electrode shape with a non-conductive coating, it will be appreciated that the non-conductive coating is applicable to either or both sides of any of the metal conductor configurations including those ofFIGS. 13A-13C.
• FIG. 14A shows a cross-section of a lead3260 that includes anouter jacket layer3266 that surrounds ashield3262 and aninner jacket layer3264. Theouter jacket layer3266 is doped withconductive particles3268 at a particular point along the length of the lead. Theseconductive particles3268 provide RF conductive qualities for theouter jacket layer3266. Thus, the RF energy couples from theshield3262 to the tissue through the dopedouter jacket layer3266. Examples of the conductive particles include carbon, tantalum, titanium, platinum, platinum-iridium, and other biocompatible conductive substances. The filars may be present within theinner jacket3264 or any other inner layer as shown or within the lumen created by the inside wall of theinner jacket3264 or any other inner layer like that shown inFIG. 12B.
• FIG. 14B shows thelead3260 with a plurality ofpoints3272 along the lead where theconductive particles3268 are present within theouter layer3266. The dopedouter layer3266 is exposed to create the RF pathway to ground from theouter layer3266 to the tissue.
• FIG. 14C shows a cross-section of a lead3260 where theouter jacket layer3266 that surrounds ashield3262 has been removed via ablation or other technique to expose theshield3262 and theinner jacket layer3264. Here, theinner jacket layer3264 is doped withconductive particles3268 at least at the particular point(s) along the length of the lead where theouter layer3266 has been removed. Theseconductive particles3268 provide RF conductive qualities for the outer portion of theinner jacket layer3264 where theshield3262 is present. Thus, the RF energy couples from theshield3262 to the tissue through the dopedjacket layer3264. The filars may be present within theinner jacket3264 or any other inner layer as shown or within the lumen created by the inside wall of theinner jacket3264 or any other inner layer like that shown inFIG. 12B.
• FIG. 14D shows thelead3260 with a plurality ofpoints3274 along the lead where theconductive particles3268 are present within theinner layer3264. Theouter layer3266 is removed at thesepoints3274 to expose the dopedinner layer3264 and to create the RF pathway to ground from theinner layer3264 to the tissue.
• FIGS. 15A and 15B show an example of an implantablemedical lead3108 where alead anchor3280 is attached. In this example, thelead anchor3280 is an RF conductor to the tissue to provide the ground pathway for theshield3118. In this particular example, thelead3108 includes aring electrode3130 that is coupled to theshield3118, either via a direct current coupling or a capacitive coupling. Thelead anchor3280 is constructed of metal or other conductor, or at least has a portion that is or conductive and directly contacts or nearly contacts thering electrode3130 and the tissue to ground theshield3118 at RF frequencies. This ground pathway is secured in place via the conventional mounting of thelead anchor3280 to the lead body and by thewings3282 being sutured in place to the tissue. The filars may be present within the inner jacket or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket or any other inner layer like that shown inFIG. 12B.
• FIGS. 15C and 15D show another example of an implantablemedical lead3108 where alead anchor3280 is attached. In this example, thelead anchor3280 is an RF conductor to the tissue to provide the ground pathway for theshield3118. In this particular example, thelead3108 does not have aring electrode3130 coupled to theshield3118. However, as seen inFIG. 15D, the lead anchor has grippingteeth3284 that sink into the outer layer of the jacket and either directly contact or nearly contact theshield3118. The filars may be present within the inner jacket or any other inner layer as shown or within the lumen created by the inside wall of the inner jacket or any other inner layer like that shown inFIG. 12B.
• Directly contacting theshield3118 creates a direct current coupled RF pathway while nearly contacting theshield3118 creates a capacitively coupled RF pathway. As with the previous example, thelead anchor3280 is constructed of metal or other conductor, or at least has a portion that is conductive and contacts or nearly contacts the tissue to ground theshield3118 at RF frequencies. This ground pathway is secured in place via the conventional mounting of the lead anchor to the lead body and by thewings3282 being sutured in place to the tissue.
• In these embodiments, the anchor may capacitively couple to theshield3118 without teeth or rings being present, particularly where the depth of the shield within theouter layer3120 is relatively small. For example, for depth of theshield3118 of about 5 mils or less, the anchor may reside on theouter layer3120 and capacitively couple to theshield3118 to provide the RF pathway to ground.
• FIG. 15E shows an example of an implantablemedical lead3108 where alead anchor3290 is attached. In this example, thelead anchor3290 is an RF conductor to the tissue to provide the ground pathway for theshield3118. However, in this particular example,lead anchor3290 provides a capacitive coupling to ground by utilizing a non-conductive outer material orcoating3292 to contact the tissue. Thelead anchor3290 may have either a direct current coupling or capacitive coupling to theshield3118, orring electrode3130 if any. The capacitive coupling to the tissue prevents thelead anchor3290 from becoming a magnetic gradient induced current electrode, such as where other shield electrodes are present at other points along thelead3108.
• Utilizing an anchor to provide an RF pathway to ground, as shown inFIGS. 15A-5E, may also be useful considering that the typical mounting location of an anchor is at a point where the intensities of the RF fields change. For instance, an anchor may be positioned near the entry hole of the cranium where thelead3108 is used for brain stimulation. The intensities of the field may change from one side of the entry hole to the other and providing the RF pathway to ground via an anchor near the entry hole may assist in dissipating energy received by theshield3118 externally of the entry hole to prevent such energy from traveling through theshield3118 and through the entry hole toward the shield termination which is closer to the stimulation electrodes.
• Embodiments disclosed in relation toFIGS. 16-17G provide for shielding of both an implantable medical lead and an implantable lead extension. The two shields are interconnected with a radio frequency (RF) conductive path to maintain a continuity of the shielding along the length between the implantable medical device (IMD) and the stimulation site.
• FIG. 16 shows an example of an implantablemedical system4100 that includes anIMD4102 coupled to alead4108. TheIMD4102 includes ametal can4104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD4102 includes aheader4106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can4104. Theheader4106 is shown transparently for purposes of illustration. Theheader4106 provides a structure for securing thelead extension4142 to theIMD4102 and for establishing electrical connectivity between circuitry of theIMD4102 and distal connectors of thelead extension4142 that are located in adistal housing4140.
• Theextension4142 also includesring connectors4110 on a proximal end that is positioned within theheader4106. Thering connectors4110 make physical contact with electrical connections within the header. The electrical connections may include a metal contact that thering connector4110 rests against upon being inserted into theheader4106 where a wire extends from the metal contact into thecan4104 where the circuitry is housed. Signals applied by theIMD4102 to thering connectors4110 are conducted through theextension4142 to the connectors within thehousing4140 to provide the stimulation signals to thelead4108. Theextension4142 is secured in theheader4106 such as by aset screw block4112 within theheader4106 that allows at least oneset screw4114 to be tightened against at least one of thering connectors4110.
• Thelead4108 includeselectrodes4116 on a distal end that are positioned at a stimulation site within a patient. Thelead4108 also includes ring connectors on a proximal end that is positioned within thehousing4140. The ring connectors make physical contact with electrical connections within thehousing4140. The electrical connections may include a metal contact such as a Bal Seal® connector of the Bal Seal Engineering, Inc. of Foothill Ranch, Calif., another spring loaded connector, or a set screw block that the electrode rests against upon being inserted into thehousing4140. A wire extends from the metal contact of thehousing4140 into theextension4142 to connect with the filars of theextension4142. Signals applied by theIMD4102 to thering connectors4110 are conducted through theextension4142 and lead4108 to theelectrodes4116 to provide the stimulation therapy to the patient.
• Thelead4108 is secured in thehousing4140 such as by a set screw block within thehousing4140 that allows at least one set screw to be tightened against at least one of the electrodes. Ashield4144 of the extension and ashield4118 of thelead4108 that are discussed below with reference toFIGS. 17A-17G are present to prevent the induced RF current on the filars. Theshields4118,4144 may be grounded at theIMD4102 ofFIG. 16 or at various grounding points established along theextension4142 and/orlead4108. As another option, theshield4144 of theextension4142 and/or theshield4118 of thelead4108 may be located within theextension4142 or lead4108 at a small distance from the surface so that theshields4118,4144 will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length. In any of these cases, continuity may be maintained between theshields4118 and4144 as discussed herein
• FIGS. 17A-17G show examples of theextension4142 and lead4108 whereshields4118,4144 are present. Thelead4108 is inserted through anopening4146 in thehousing4140 on the distal end of theextension4142.Outer jacket layers4120,4141 for thelead4108 andextension4142 are shown transparently inFIG. 17A for purposes of illustrating theshields4118,4144. Theshields4118,4144 block at least some RF energy from directly coupling to conductive filars that are present within thelead4108 andextension4142. The conductive filars extend the length of theextension4142 and lead4108 and interconnect the proximal connector rings4110 of theextension4142 to thedistal electrodes4116 of thelead4108 so that stimulation signals are conducted to the stimulation site.
• As shown inFIG. 17A, theshields4118,4144 of this example are braided metal wires. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desirable to utilize a biocompatible metal for theshields4118,4144, particularly for embodiments where a portion of theshields4118,4144 may be exposed for purposes of grounding. While theshield4118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead4108 in an overlapping manner or anouter layer4120 that is heavily doped with conductive particles.
• FIG. 17A also shows aset screw block4143 present on thehousing4140. Theset screw block4143 may be used to fix the proximal end of thelead4108 in place within theopening4146 of thehousing4140 where a set screw is tightened against a connector ring on thelead4108. Other manners of fixing thelead4108 withinhousing4140 may also be used.
• FIG. 17B shows a coupling of thelead4108 to thehousing4140 as a cross-section taken through the coupling of ashield connector4132 to ashield electrode4130. Theshield4118 of thelead4108 may be embedded within the jacket of thelead4108. One manner of constructing thelead4108 with theshield4118 is to provide aninner jacket4122 that encloses thefilars4124 and anyadditional insulation layer4126, such as polytetrafluoroethylene (PTFE) that may surround each filar4124. Theshield4118 may then reside on the outer portion of theinner jacket4122, and theouter jacket4120 may then enclose theshield4118. Theouter jacket4120 maybe added over thebraid4118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield4118 to RF couple to tissue, typically as a capacitive coupling, either as an alternative to or in addition to grounding at the can of the IMD or elsewhere, the amount of theouter jacket layer4120 covering theshield4118 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield4118 grounds at the can of the IMD and grounding via a capacitive coupling from the shield through theouter jacket4120 directly to the tissue is of less significance, then theshield4118 may be located further from the outer surface of thelead4108.
• The inner andouter jackets4122,4120 may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes, and silicones. Alumen4128 may be included inside of theinner jacket4122 around which theinsulated filars4124 are coiled or otherwise positioned. Thelumen4128 may be useful, particularly for percutaneous leads4108, to allow a stylet to be inserted for purposes of pushing and steering thelead4108 into the desired position within the patient.
• To provide a robust connection for theshield4118, theshield electrode4130 such as an electrode ring may be wrapped around theouter layer4120 to contact theshield4118 and provide a direct current coupling to theshield4118. A direct current coupling between the shields avoids large variations in the characteristic impedance for the shielding from theextension4142 to thelead4108. Avoiding variations in the characteristic impedances may reduce the degree of RF reflection that occurs within theshield4118, which in turn reduces the amount of RF heating that may occur via the stimulation electrodes.
• Thehousing4140 includes theshield connector4132, such as a set screw block, a Bal Seal® connector, or another spring loaded connector. Theshield connector4132 of this embodiment is enclosed within ahousing layer4134 and contacts theshield electrode4130 of thelead4108. Thehousing layer4134 may be constructed of various non-conductive materials such as polyurethane, polysulfone, nylon, silicone and polyetheretherketone (PEEK) and provides a relatively rigid structure similar to that provided by theheader4106 of theIMD4102.
• Ashield jumper wire4136 is included in this embodiment within thehousing layer4134. Theshield jumper wire4136 contacts theshield connector4132 and extends from theshield connector4132 into thehousing layer4134 and extends proximally to theshield4144 within theextension4142. Theshield jumper wire4136 may be welded, crimped, or otherwise affixed to theshield conductor4132 and theshield4144.
• FIG. 17C shows an example similar to the example ofFIG. 17B. Thelead4108 is constructed in the same manner. However, thehousing4140 utilizes a different construction. In thehousing4140, ahousing shield4138 is present and extends to theshield conductor4132 where thehousing shield4138 contacts theshield connector4132. No jumper wire is needed because thehousing shield4138 establishes continuity of the shielding from theshield connector4132 to theshield4144 present within theextension4142.
• Thehousing shield4138 may be affixed to theshield connector4132 in various ways. For instance, thehousing shield4138 may be welded or crimped to theshield connector4132 to provide a direct current coupling. In some embodiments, theshield connector4132 is distal relative to stimulation connectors of thehousing4140. In those cases, extending thehousing shield4138 through thehousing4140 to theshield connector4132 provides additional shielding protection from RF induced currents.
• FIG. 17D shows thelead4108 coupled to thehousing4140 with a cross-section through a stimulation electrode coupling for embodiments of thehousing4140 that include ashield jumper wire4136. Thelead4108 includes astimulation connector4150 and astimulation jumper wire4156 that interconnects the filar4124 to thestimulation connector4150. Thehousing4140 includes astimulation connector4152 that contacts thestimulation connector4150 to form a direct current coupling. Astimulation jumper wire4154 of thehousing4140 contacts thestimulation connector4152 and extends through thehousing layer4134 in the proximal direction to a corresponding filar within theextension4142.
• As shown inFIG. 17D, both theshield jumper wire4136 and thestimulation jumper wire4154 are present within thehousing layer4134. Separation between them is provided to avoid transferring significant RF energy being captured by theshields4118,4144 from theshield jumper wire4136 to thestimulation jumper wire4154. For instance, the separation may be in the range of 0.1 millimeters (mm) to 2.0 mm where thehousing layer4134 is constructed of polyurethane, polysulfone, nylon, and PEEK or has a dielectric property of between about 2 and 10.
• FIG. 17E shows thelead4108 coupled to thehousing4140 with a cross-section through a stimulation connector coupling for embodiments of thehousing4140 that include thehousing shield4138 extending through thehousing4140. Thelead4108 includes thestimulation connector4150 and thestimulation jumper wire4156 that interconnects the filar4124 to thestimulation connector4150. Thehousing4140 includes thestimulation connector4152 that contacts thestimulation connector4150 to form a direct current coupling. Thestimulation jumper wire4154 of thehousing4140 contacts thestimulation connector4152 and extends in the proximal direction to a corresponding filar within theextension4142.
• As shown inFIG. 17E, thehousing shield4138 and thestimulation jumper wire4154 are present within different layers of housing material. Thestimulation jumper wire4154 is present within a housinginner layer4162 while thehousing shield4138 is present about the housinginner layer4162. A housingouter layer4160 surrounds thehousing shield4138 and the housinginner layer4162. The housinginner layer4162 and the housingouter layer4160 may be constructed of various non-conductive materials such as those discussed above for thehousing layers4134, and theselayers4160,4162 may be the same or different non-conductive materials. Separation like that discussed above between thestimulation jumper wire4154 and thehousing shield4138 is provided to avoid transferring significant RF energy being captured by theshields4118,4144 from thehousing shield4138 to thestimulation jumper wire4154.
• FIG. 17F shows an embodiment of thehousing4140 where theshield jumper wire4136 is present. Theshield jumper wire4136 has anattachment point4172 such as a weld or crimp to theshield connector4132 where theshield electrode4130 is seated. Theshield jumper wire4136 has anotherattachment point4184 such as a weld or crimp to theshield4144 of theextension4142.
• Thestimulation jumper wires4154,4182 haveattachment points4174,4178 such as a weld or crimp to thestimulation connectors4152 where thestimulation electrodes4150,4176 are seated. Only twostimulation jumper wires4154,4182 are shown for purposes of clarity, and it will be appreciated that any number of stimulation connectors and corresponding stimulation jumper wires may be present within thehousing4140. As shown, separation is provided between theshield jumper wire4136 and thestimulation jumper wires4154,4182 to avoid transferring RF energy to thestimulation jumper wires4154,4182.
• FIG. 17G shows an embodiment of thehousing4140 where thehousing shield4138 is present. Thehousing shield4138 has attachment points4186 such as welds or crimps to theshield connector4132 where theshield electrode4130 is seated. Thehousing shield4138 continues through the housing outlayer4160 while surrounding the housinginner layer4162. Thehousing shield4138 transitions to theextension shield4144 upon reaching the junction of thehousing4140 to the body of theextension4142. In other embodiments, thehousing shield4138 may be attached to theshield4144 via welds or crimps rather than transitioning into the body of theextension4142 as theshield4144.
• Thestimulation jumper wires4154,4182 haveattachment points4174,4178 to thestimulation connectors4152 where thestimulation electrodes4150,4176 are seated. As shown, separation is provided between thehousing shield4138 and thestimulation jumper wires4154,4182 to avoid transferring RF energy to thestimulation jumper wires4154,4182.
• Embodiments as disclosed in relation toFIGS. 18-29 provide for termination of a radio frequency (RF) shield present within an implantable medical lead for use with an implantable medical device (IMD). The shield may be terminated in various ways such as by terminating at an edge of a butt, scarf, or lap joint to an insulation extension. Furthermore, the shield termination may include features such as a ring attached at the shield termination point within the insulation, shield wires with folded over ends, or barbs between the insulation layers.
• FIG. 18 shows an example of an implantablemedical system5100 that includes anIMD5102 coupled to alead5108. TheIMD5102 includes ametal can5104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD5102 includes aheader5106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can5104. Theheader5106 is shown transparently for purposes of illustration. Theheader5106 provides a structure for securing thelead5108 to theIMD5102 and for establishing electrical connectivity between circuitry of theIMD5102 and electrodes of thelead5108.
• Thelead5108 includeselectrodes5116 on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings5110 on a proximal end that is positioned within theheader5106. The connector rings5110 make physical contact withelectrical connections5111 within the header. Theelectrical connections5111 may include a metal contact that theconnector ring5110 rests against upon being inserted into theheader5106 where a wire extends from the metal contact into thecan5104 where the circuitry is housed. Signals applied by theIMD5102 to the connector rings5110 are conducted through thelead5108 to theelectrodes5116 to provide the stimulation therapy to the patient.
• Thelead5108 is secured in theheader5106 such as by aset screw block5112 within theheader5106 that allows at least oneset screw5114 to be tightened against at least one of the connector rings5110. Ashield5118 as shown inFIGS. 19A and 19B may be grounded to the body along one or more points down the length of the lead from theIMD5102 via ground rings and/or theshield5118 may be grounded at thecan5104 of theIMD5102 ofFIG. 18. As another option, theshield5118 may be located within thelead5108 at a small distance from the surface so that theshield5118 will effectively capacitively couple to the tissue along the length of the lead to dissipate energy to the tissue over the length.
• Regardless of the manner of grounding, theshield5118 terminates on one end near the proximal end and on the opposite end near the distal end of thelead5108. At the termination point, shields having multiple metal wires such as braided shields are subject to fraying and shield wire migration. Preventing the shield wire from fraying and/or migrating to the tissue or to stimulation conductors within thelead5108 may be desirable to prevent RF energy captured by theshield5118 from being directed onto a small area of tissue via an electrode or exposed shield wire.
• FIGS. 19A and 19B show an example of thelead5108, where ashield5118 is present. Anouter insulation layer5120 of a lead jacket is shown transparently inFIG. 19A for purposes of illustrating theshield5118. Theshield5118 blocks at least some RF energy from directly coupling toconductive filars5124 that are present within thelead5108. Theconductive filars5124 extend the length of the lead and interconnect theproximal electrodes5110 to thedistal electrodes5116 so that stimulation signals are conducted from the proximal end to the distal end of thelead5108.
• As shown inFIG. 19A, theshield5118 of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield5118, particularly for embodiments where a portion of theshield5118 may be exposed for purposes of grounding. While theshield5118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead5108 in an overlapping manner or anouter layer5120 that is heavily doped with conductive particles.
• As shown inFIG. 19B, theshield5118 may be embedded within the jacket of thelead5108. One manner of constructing thelead5108 with theshield5118 is to provide aninner insulation layer5122 of the jacket that encloses thefilars5124 and anyadditional insulation layer5126, such as polytetrafluoroethylene (PTFE) that may surround each filar5124. Theshield5118 may then reside on the outer portion of theinner insulation layer5122, and theouter insulation layer5120 may then enclose theshield5118. Theouter jacket5120 maybe added over thebraid5118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield5118 to RF couple to tissue, typically as a capacitive coupling, either as an alternative to grounding at thecan5104 of theIMD5102 or at specific points along thelead5108 or in addition to such grounds, the amount of theouter jacket layer5120 covering theshield5118 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield5118 grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, theshield5118 may be located further from the outer surface of thelead5108 with additional features of the lead providing the coupling at the one or more specific locations as discussed below.
• The inner andouter insulation layers5122,5120 of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethane, and silicones. Alumen5128 may be included inside of theinner jacket5122 around which theinsulated filars5124 are coiled or otherwise positioned. Thelumen5128 may be useful, particularly for percutaneous leads5108, to allow a stylet to be inserted for purposes of pushing and steering thelead5108 into the desired position within the patient.
• FIG. 20 shows an embodiment of an implantablemedical lead5108 in cross-section with a cut taken down an axial centerline. Thelead5108 terminates at a butt joint5130 where theinner insulation layer5122,shield5118, andouter insulation layer5120 terminate. At this butt joint5130, aninsulation extension5132 abuts and is bonded via RF heating, thermal, reflow, or similar processes to the blunt ends of theinner insulation layer5122,outer insulation layer5120, andshield5118.
• As shown in this example, theshield5118 terminates at the butt joint5130 rather than farther back within the jacket formed by the inner andouter insulation layers5122,5120. Theinsulation extension5132 in this example extends the remainder of thelead5108 wherering electrodes5134 are located. Thefilars5124 jumper to their respective ring electrodes via afilar jumper5136. The lumen may be present with thefilars5124 being located about the lumen.
• The material for theinsulation extension5132 may be selected to provide more or less stiffness than the inner andouter insulation layers5122,5120, depending upon which end of the lead the butt joint5130 is located. For instance, where theelectrode5134 is on the proximal end of thelead5108 and is being positioned within theheader5106 of theIMD5102, theinsulation extension5132 may be constructed of a stiffer material. Where theelectrode5134 is on the distal end of thelead5108 and is being steered to the stimulation site within the body, theinsulation extension5132 may be constructed of a more flexible material.
• Using a stiffer material as theinsulation extension5132 on the proximal end aids in the insertion of the proximal end into theheader5106. As a particular example, theouter insulation5120 may be constructed of polyurethane having a durometer 55D or similar rating while theinsulation extension5132 may be constructed of a polyurethane having a durometer 75D or similar rating.
• Using a less stiff material as theinsulation extension5132 on the distal end aids in the positioning of the distal end at the stimulation site. As a particular example, theouter insulation5120 may be constructed of polyurethane having a durometer 55D or similar rating while theinsulation extension5132 may be constructed of polyurethane having a durometer 80A or similar rating.
• The gap between the termination of theshield5118 at the butt joint5130 and the nearest edge of theelectrode5134 is selected to avoid RF problems. In particular, the distance is selected so that RF coupling is avoided while the unshielded region of thefilars5124 is not overly exposed to RF. For MRI frequencies that typically range from 43 MHz to 128 MHz, a spacing of from 0.5 mm to 10 cm may be acceptable for these embodiments.
• FIG. 21 shows another embodiment of an implantablemedical lead5108 in cross-section with a cut taken down an axial centerline. Thelead5108 terminates at a scarf joint5140 where theinner insulation layer5122,shield5118, andouter insulation layer5120 terminate at a wedged cut. At this scarf joint5140, aninsulation extension5132 that has a complementary wedged cut abuts and is bonded to the wedged end of theinner insulation layer5122,outer insulation layer5120, andshield5118 via RF heating, thermal, reflow or similar processes.
• The scarf joint5140 may be used rather than the butt joint5130 ofFIG. 20 because the scarf joint5140 increases the bonding area. As shown in this example, theshield5118 terminates at the scarf joint5140 rather than farther back within the jacket formed by the inner andouter insulation layers5122,5120. Theinsulation extension5132 in this example extends the remainder of thelead5108 wherering electrodes5134 are located. Thefilars5124 jumper to their respective ring electrodes via afilar jumper5136.
• Similar to the previous embodiment ofFIG. 20, the material for theinsulation extension5132 in this embodiment ofFIG. 4 may be selected to provide more or less stiffness than the inner andouter insulation layers5122,5120, depending upon which end of the lead the scarf joint5140 is located. For instance, where theelectrode5134 is on the proximal end of thelead5108 and is being positioned within theheader5106 of theIMD5102, theinsulation extension5132 may be constructed of a stiffer material such as polyurethane with a durometer 75D. Where theelectrode5134 is on the distal end of thelead5108 and is being steered to the stimulation site within the body, theinsulation extension5132 may be constructed of a more flexible material such as polyurethane with a durometer 80A.
• The gap between the termination of theshield5118 at the butt joint5130 and thenearest electrode5134 is selected to avoid RF problems. In particular, the distance is selected so that RF coupling is avoided while the unshielded region of thefilars5124 is not overly exposed to RF. For MRI frequencies that typically range from 43 MHz to 128 MHz, spacing between the edge of theelectrode5134 nearest the scarf joint5140 and the termination of theshield5118 at the scarf joint5140 may range from 0.5 mm to 10 cm for these embodiments. With the scarf joint5140 ofFIG. 21, the spacing between the termination of theshield5118 and theelectrode5134 varies for different locations around the circumference of the scarf joint5140, but the shortest spacing is maintained at 0.5 mm or above and the longest spacing is maintained at 10 cm or below.
• FIG. 22 shows a set of steps to create the embodiments ofFIGS. 20 and 21. Initially, a structure including theinner insulation layer5122,outer insulation layer5120, andshield5118 may be provided. Theshield5118 has been braided over theinner insulation layer5122 and then theouter insulation layer5120 has been positioned and reflowed or otherwise bonded over theinner insulation layer5122 and theshield5118. To begin construction of thelead5108 and the butt joint5130 or scarf joint5140, the structure is cut to size by making a cut through the insulation layers5120,5122 and theshield5118 at acutting step5142. For a butt joint5130, the cut is perpendicular to the axial dimension to create the blunt end. For a scarf joint5140, the cut is at angle other than 90 degrees to the axial dimension to create the wedged end.
• Theinsulation extension5132 is also provided with a complementary end to bond to thelead5108 to form the butt joint5130 or scarf joint5140. For the butt joint5130, theinsulation extension5132 is cut perpendicular to the axial dimension to create the blunt end. For the scarf joint5140, theinsulation extension5132 is cut at an angle other than 90 degrees to the axial dimension to create the wedged end. The two blunt ends for the butt joint5130 are brought together and bonded at abonding step5144. Likewise, the two wedged ends for the scarf joint5140 are brought together and bonded at thebonding step5144.
• FIG. 23 shows another embodiment of an implantablemedical lead5108 in cross-section with a cut taken down an axial centerline. Thelead5108 terminates at a lap joint5150. The lap joint5150 involves removing an end portion of theouter insulation layer5120 and applying a replacementouter insulation layer5152 onto the area of theshield5118 andinner insulation layer5122 where theouter insulation layer5120 is missing. The replacementouter insulation layer5152 also laps over a section of theinsulation extension5132 and may extend to thenearest electrode5134.
• As shown, theshield5118 has been crimped down into theinner insulation layer5122 at the region where theouter insulation layer5120 has been removed. Doing so prevents theshield5118 from bunching together during installation of the outerreplacement insulation layer5152. This may be especially the case where the replacementouter insulation layer5152 is in the form of tubing that slides into place over theshield5118 andinner insulation layer5122 prior to attaching theinsulation extension5132. Where the replacementouter insulation layer5152 is tubing, once being slid into place, it is reflowed or otherwise bonded to theinner insulation layer5122. As an alternative, the replacementouter insulation layer5152 may be injection molded into place.
• As shown in this example, theshield5118 terminates at the lap joint5150 rather than farther back within the jacket formed by the inner andouter insulation layers5122,5120. Theinsulation extension5132 in this example extends the remainder of thelead5108 wherering electrodes5134 are located. Thefilars5124 jumper to their respective ring electrodes via afilar jumper5136. The lumen may be present in some embodiments with thefilars5124 being located about the lumen.
• In this embodiment the replacementouter insulation layer5152 may be constructed of a material that differs in stiffness from theouter insulation layer5120 depending upon which end of thelead5108 the lap joint5150 is located. For instance, where theelectrode5134 is on the proximal end of thelead5108 and is being positioned within theheader5106 of theIMD5102, the replacementouter insulation layer5152 may be constructed of a stiffer material such as durometer 75D polyurethane. Where theelectrode5134 is on the distal end of thelead5108 and is being steered to the stimulation site within the body, the replacementouter insulation layer5152 may be constructed of a more flexible material such as 80A polyurethane.
• In this embodiment, like that of the previous ones, the material for theinsulation extension5132 may also be selected to provide more or less stiffness than the inner andouter insulation layers5122,5120, depending upon which end of the lead the lap joint5150 is located. For instance, where theelectrode5134 is on the proximal end of thelead5108 and is being positioned within theheader5106 of theIMD5102, theinsulation extension5132 may be constructed of a stiffer material such as durometer 75D polyurethane. Where theelectrode5134 is on the distal end of thelead5108 and is being steered to the stimulation site within the body, theinsulation extension5132 may be constructed of a more flexible material such as 80A polyurethane.
• The gap between the termination of theshield5118 at the lap joint5150 and thenearest electrode5134 is also selected to avoid RF problems. For MRI frequencies, a spacing of from 0.5 mm to 10 cm may be acceptable for these embodiments.
• FIG. 24 shows one example of a set of steps that create thelap joint5150 ofFIG. 23. Initially, a structure including theinner insulation layer5122,outer insulation layer5120, andshield5118 may be provided. Theshield5118 has been braided over theinner insulation layer5122 and then theouter insulation layer5120 has been positioned and reflowed or otherwise bonded over theinner insulation layer5122 and theshield5118. To begin construction of thelead5108 and the lap joint5150, the structure is cut to size by making a cut through the insulation layers5120,5122 and theshield5118 at acutting step5154. For a lap joint5150, this first cut is perpendicular to the axial dimension to create a blunt end.
• Once cut to size, theouter insulation layer5120 is then ablated by some distance to expose theshield5118 and theinner insulation layer5122 at anablating step5156. Ablation may be done using tools such as an excimer laser which can very precisely ablate to expose theshield5118. The length of theouter insulation layer5120 to be ablated may vary, but an illustrative range is from 0.25 centimeters (cm) to 5 cm.
• Once ablation is complete, the next step may vary. The replacementouter insulation layer5152 may be installed in various manners such as by reflowing tubing or by injection molding. If by injection molding, then the next step may be either a crimpingstep5158 or aninjecting step5162. If by reflowing tubing, then it may be helpful to proceed to the crimpingstep5158 after ablating.
• At the crimpingstep5158, theshield5118 is crimped so as to sink down into theinner insulation layer5122 at the area where theouter insulation layer5120 has been removed. If a ring or other tool is used to crimp theshield5118 into theinner insulation layer5122, the ring or other tool may then be removed. Where the replacementouter insulation layer5152 is being installed as tubing that is reflowed, then the next step istubing step5160. Where the replacementouter insulation layer5152 is being installed by injection molding, then the next step is injectingstep5162.
• At thetubing step5160, the tubing is slid onto theinner insulation layer5122 and over theshield5118 at the area where theouter insulation layer5120 has been removed and where theshield5118 has been crimped down. The tubing extends beyond the end of theinner insulation layer5122 so that it may eventually be bonded to theinsulation extension5132. The tubing is reflowed, RF heated, etc. to bond to theinner insulation layer5122 and to the end of theouter insulation layer5120 where the ablating stopped to form the replacementouter insulation layer5152. Contemporaneously or sequentially, theinsulation extension5132 is bonded in place at the blunt end of theinner insulation layer5122 and to the tubing of the replacementouter insulation layer5152 that extends beyond theinner insulation layer5122 at abonding step5164. This tubing may be reflowed, RF heated, etc. onto theinsulation extension5132.
• Returning to the injectingstep5162, in the scenario where the replacementouter insulation layer5152 is to be injection molded, then the injectingstep5126 takes place either after theablating step5156 or after the crimpingstep5158. Material such as the desired polyurethane is injected onto theinner insulation layer5122 and theshield5118 to form the replacementouter insulation layer5152. Contemporaneously, theinsulation extension5132 is bonded to theinner insulation layer5122 and to the replacementouter insulation layer5152 at thebonding step5164.
• Alternative manners of creating the lap joint5150 may also be used. For instance, the structure of theouter insulation layer5120,inner insulation layer5122, andshield5118 may be bonded to theinsulation extension5132 via a butt joint. Then, the area where the replacementouter insulation layer5152 will be positioned that is currently occupied by theouter insulation layer5120 is ablated. Theinsulation extension5132 is also ablated at the same or similar depth as theouter insulation layer5120. The replacementouter insulation layer5152 may then be injection molded or shrunk into position at the ablation site.
• FIG. 25 shows an embodiment with an additional feature that may be included for the lap joint5150. To further protect the termination of theshield5118 from fraying or migrating, the wire ends of theshield5118 may be capped with aring5166. Thering5166 may be metal, plastic, or similar materials. In this example, aregion5168 of theinner insulation layer5122 has been ablated to allow the ring to be positioned over the ends of the wires of theshield5118.
• FIG. 26 shows an embodiment with an additional feature that may be included for the butt or scarf joints5130,5140. To further protect the termination of theshield5118 from fraying or migrating, the wire ends of theshield5118 may be capped with aring5170. Similar to the lap joint scenario, thering5170 may be metal, plastic, or similar materials. In this example, aregion5172 of theouter insulation layer5120 has been ablated to allow thering5170 to be positioned over the ends of the wires of theshield5118, and then thisregion5172 may be filled using a reflow or injection molding of the polyurethane or other polymer.
• FIG. 27 shows an embodiment with an additional feature that may be included for a joint5176, which may be of various types such as the butt, scarf, orlap joints5130,5140, and5150. At the joint5176, theouter insulation layer5120 of thelead5108 encounters anotherlayer5178. Thislayer5178 may be theinsulation extension5132 and/or the replacementouter insulation layer5152. In either case, wires of theshield5118 may partially extend into thelayer5178. However, prior to bonding thelayer5178 to thelayers5120 or5122, the ends of the wires of theshield5118 may be individually folded over as shown inFIG. 27. In this manner, the folded over ends are less likely to fray and migrate.
• FIG. 28 shows an embodiment with another feature that may be included for a joint at the termination of theshield5118 to assist in holding the bond between theinner insulation layer5122 and theinsulation extension5132 in place. In this example, a lap joint5150 is shown, but it will be appreciated that this feature may be applicable to other joints as well including butt and scarf joints5130,5140. Here, the replacementouter insulation layer5152 may be tubing that is provided withbarbs5151 that extend toward theinner insulation layer5122 and theshield5118.
• During reflow, the barbs may sink into theinner insulation layer5122 as theinner insulation layer5122 softens more so than thebarbs5151, and the replacementouter insulation layer5152 descends into position. Thebarbs5151 may also sink into theinsulation extension5132 once reflow or other bonding is attempted after theinsulation extension5132 has been inserted to provide extra grip between the replacementouter insulation layer5152 and theinsulation extension5132. Thebarbs5151 then provide extra grip between theinner insulation layer5122 and theinsulation extension5132 particularly during axial tension. Rather than incorporating the barbs into the replacementouter tubing5152 of the lap joint example, a separate barbed ring may be positioned on theinner insulation layer5122 and then the replacementouter insulation layer5152 is reflowed or otherwise bonded into place.
• FIG. 29 shows an embodiment with another feature that may be included for a joint at the termination of theshield5118 to assist in holding the bond between theinner insulation layer5122 and theinsulation extension5132 in place. In this example, a lap joint5150 is shown, but it will be appreciated that this feature may be applicable other joints as well including butt and scarf joints5130,5140. Here, abarbed ring5153 is positioned inside of theinner insulation layer5122 and is forced to expand radially until the barbs of thebarbed ring5153 sink into theinner insulation layer5122. The barbs of thebarbed ring5153 may also sink into the inside of theinsulation extension5132. Thebarbed ring5153 provides extra grip between theinner insulation layer5122 and theinsulation extension5132 especially during axial tension. Thisbarbed ring5153 feature may also be used in conjunction with thebarbs5151 shown inFIG. 28.
• Embodiments as disclosed in relation toFIGS. 30-48 also provide for termination of a radio frequency (RF) shield present within an implantable medical lead for use with an implantable medical device (IMD). The shield may be terminated in various ways such as by terminating at a joint to an insulation extension where one or more metal connectors are present in various configurations to provide a ground path for the shield. Furthermore, the shield termination may include features such as a shield wires with folded over ends, or barbs between the insulation layers.
• FIG. 30 shows an example of an implantablemedical system6100 that includes anIMD6102 coupled to alead6108. TheIMD6102 includes ametal can6104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD6102 includes aheader6106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can6104. Theheader6106 is shown transparently for purposes of illustration. Theheader6106 provides a structure for securing thelead6108 to theIMD6102 and for establishing electrical connectivity between circuitry of theIMD6102 and electrodes of thelead6108.
• Thelead6108 includeselectrodes6116 on a distal end that are positioned at a stimulation site within a patient. The lead also includesring connectors6110 on a proximal end that is positioned within theheader6106. Thering connectors6110 make physical contact withelectrical connections6111 within the header. Theelectrical connections6111 may include a metal contact that thering connector6110 rests against upon being inserted into theheader6106 where a wire extends from the metal contact into thecan6104 where the circuitry is housed. Signals applied by theIMD6102 to thering connectors6110 are conducted through thelead6108 to theelectrodes6116 to provide the stimulation therapy to the patient.
• Thelead6108 is secured in theheader6106 such as by aset screw block6112 within theheader6106 that allows at least oneset screw6114 to be tightened against at least one of thering connectors6110. Ashield6118 as shown inFIGS. 31A and 31B may be grounded to the body along one or more points down the length of the lead from theIMD6102 via ground rings and/or theshield6118 may be grounded at thecan6104 of theIMD6102 ofFIG. 30.
• Regardless of the manner of grounding, theshield6118 terminates on one end near the proximal end and on the opposite end near the distal end of thelead6108. At the termination point, shields having multiple metal wires such as braided shields are subject to fraying and shield wire migration. Preventing the shield wire from fraying and/or migrating to the tissue or to stimulation conductors within thelead6108 may be desirable to prevent RF energy captured by theshield6118 from being directed onto a small area of tissue via an electrode or exposed shield wire.
• FIGS. 31A and 31B show an example of thelead6108, where ashield6118 is present. Anouter insulation layer6120 of a lead jacket is shown transparently inFIG. 31A for purposes of illustrating theshield6118. Theshield6118 blocks at least some RF energy from directly coupling toconductive filars6124 that are present within thelead6108. Theconductive filars6124 extend the length of the lead and interconnect theproximal ring connectors6110 to thedistal electrodes6116 so that stimulation signals are conducted from the proximal end to the distal end of thelead6108.
• As shown inFIG. 31A, theshield6118 of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield6118, particularly for embodiments where a portion of theshield6118 may be exposed for purposes of grounding. While theshield6118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead6108 in an overlapping manner or anouter layer6120 that is heavily doped with conductive particles.
• As shown inFIG. 31B, theshield6118 may be embedded within the jacket of thelead6108. One manner of constructing thelead6108 with theshield6118 is to provide aninner insulation layer6122 of the jacket that encloses thefilars6124 and anyadditional insulation layer6126, such as polytetrafluoroethylene (PTFE) that may surround each filar6124. Theshield6118 may then reside on the outer portion of theinner insulation layer6122, and theouter insulation layer6120 may then enclose theshield6118. Theouter insulation layer6120 may be added over theshield6118 and shrunk in place or may be extruded over theshield6118. Theouter jacket6120 maybe added over thebraid6118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield6118 to RF couple to tissue, typically as a capacitive coupling, in addition to grounding at the can or along the lead, the amount of theouter jacket layer6120 covering theshield6118 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield6118 grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, theshield6118 may be located further from the outer surface of thelead6108.
• The inner andouter insulation layers6122,6120 of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. Alumen6128 may be included inside of theinner jacket6122 around which theinsulated filars6124 are coiled or otherwise positioned. Thelumen6128 may be useful, particularly for percutaneous leads6108, to allow a stylet to be inserted for purposes of pushing and steering thelead6108 into the desired position within the patient.
• FIG. 32 shows an embodiment of an implantablemedical lead6108 in cross-section with a cut taken down an axial centerline. Thelead6108 includes a butt joint6130 where theinner insulation layer6122 andshield6118 terminate. Theouter insulation6120 terminates prior to the butt joint6130 to expose theshield6118 andinner insulation layer6122. Ametal connector6131 is positioned over theshield6118 andinner insulation layer6122 and abuts the end of theouter insulation layer6120. At the butt joint6130, aninsulation extension6132 abuts and is bonded to the blunt end of theinner insulation layer6122,shield6118, andmetal connector6131 such as via reflow or injection molding.
• As shown in this example, theshield6118 terminates at the butt joint6130 rather than farther back within the jacket formed by the inner andouter insulation layers6122,6120. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located on the proximal end at a separate from the nearest connector ring ranging from about 0.5 millimeters to about 10 centimeters. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• The material for theinsulation extension6132 may be selected to provide a different amount of stiffness than the inner andouter insulation layers6122,6120. For instance, theinsulation extension6132 may be constructed of a stiffer material to aid in the insertion of the proximal end into theheader6106. As a particular example, theouter insulation6120 may be constructed of polyurethane having a durometer 55D or similar rating while theinsulation extension6132 may be constructed of a polyurethane having a durometer 75D or similar rating.
• Theshield6118 may be terminated with an exposedmetal connector6131 at a butt joint on the distal end so long as no terminating ground ring is present at the proximal end to thereby avoid stimulation induced by magnetic gradients. In such a case, the insulation extension may have a durometer rating similar to theouter layer6120 but may instead be constructed of polyurethane having a durometer 80A or similar rating.
• Themetal connector6131 is separated from the distal electrode by at least 0.5 mm up to 10 cm for some body locations, to avoid excessive RF coupling to the distal electrode, with 2 mm being one example of spacing that provides adequate filar coverage with insignificant coupling to the distal electrode. Where the distal end is located in a high RF intensity area such as just under the skin for peripheral nerve stimulation, then the distance may be kept smaller, such as less than 2 cm to avoid overexposure of thefilars6124.
• FIG. 33 shows another embodiment of an implantablemedical lead6108 in cross-section with a cut taken down an axial centerline. Thelead6108 terminates at a scarf joint6140 where theinner insulation layer6122 andshield6118 terminate at a wedged cut. Theouter insulation6120 terminates prior to the scarf joint6140 to expose theshield6118 andinner insulation layer6122. Ametal connector6131 is positioned over theshield6118 andinner insulation layer6122 and abuts the end of theouter insulation layer6120. At this scarf joint6140, aninsulation extension6132 that has a complementary wedged cut abuts and is bonded to the wedged end of theinner insulation layer6122,shield6118, andmetal connector6131 such as via reflow or injection molding.
• The scarf joint6140 may be used rather than thebutt joint6130 ofFIG. 32 because the scarf joint6140 has an increased bond area. As shown in this example, theshield6118 terminates at the scarf joint6140 rather than farther back within the jacket formed by the inner andouter insulation layers6122,6120. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located on the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136.
• Similar to the previous embodiment ofFIG. 32, the material for theinsulation extension6132 in this embodiment ofFIG. 33 may be selected to provide a different stiffness than the inner andouter insulation layers6122,6120. For instance, theinsulation extension6132 may be constructed of a stiffer material such as polyurethane with a durometer 75D.
• Themetal connector6131 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connector6131 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 34 shows a set of steps to create the embodiments ofFIGS. 32 and 33. Initially, a structure including theinner insulation layer6122,outer insulation layer6120, andshield6118 may be provided. Theshield6118 has been braided over theinner insulation layer6122 and then theouter insulation layer6120 has been positioned and reflowed or otherwise bonded over theinner insulation layer6122 and theshield6118. To begin construction of thelead6108 and the butt joint6130 or scarf joint6140, the structure is cut to size by making a cut through the insulation layers6120,6122 and theshield6118 at acutting step6142. For a butt joint6130, the cut is perpendicular to the axial dimension to create the blunt end. For a scarf joint6140, the cut is at angle other than 90 degrees to the axial dimension to create the wedged end.
• The end portion of theouter insulation layer6120 is ablated to reveal theshield6118 at ablatingstep6144. Themetal connector6131, such as a ring connector, may then be crimped or welded onto theshield6118 at crimpingstep6146.
• Theinsulation extension6132 is bonded to thelead6108 to form the butt joint6130 or scarf joint6140 at abonding step6148. For the butt joint6130, theinsulation extension6132 is cut perpendicular to the axial dimension to create the blunt end. For the scarf joint6140, theinsulation extension6132 is cut at an angle other than 90 degrees to the axial dimension to create the wedged end. The two blunt ends for the butt joint6130 are brought together and bonded at abonding step6148. Likewise, the two wedged ends for the scarf joint6140 are brought together and bonded at thebonding step6148.
• FIG. 35 shows another embodiment of an implantablemedical lead6108 in cross-section with a cut taken down an axial centerline. Thelead6108 includes a lap joint6150 where theinner insulation layer6122 and theshield6118 terminate. The lap joint6150 involves removing an end portion of theouter insulation layer6120 sufficient to allow space for themetal connector6131 and a replacementouter insulation layer6152 to lap over the area of theshield6118 andinner insulation layer6122 where theouter insulation layer6120 is missing. Themetal connector6131 abuts the end of theouter insulation layer6120. The replacementouter insulation layer6152 abuts themetal connector6131, laps over a section of theinsulation extension6132, and may extend to thenearest electrode6134.
• As shown, theshield6118 has been crimped down into theinner insulation layer6122 at the region where theouter insulation layer6120 has been removed. Doing so prevents theshield6118 from bunching together during installation of the outerreplacement insulation layer6152. This may be especially the case where the replacementouter insulation layer6152 is in the form of tubing that slides into place over theshield6118 andinner insulation layer6122 prior to attaching theinsulation extension6132. Where the replacementouter insulation layer6152 is tubing, once being slid into place, it is reflowed or otherwise bonded to theinner insulation layer6122. As an alternative, the replacementouter insulation layer6152 may be injection molded into place.
• As shown in this example, theshield6118 terminates at the lap joint6150 rather than farther back within the jacket formed by the inner andouter insulation layers6122,6120. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• In this embodiment the replacementouter insulation layer6152 may be constructed of a material that differs in stiffness from theouter insulation layer6120. For instance, the replacementouter insulation layer6152 may be constructed of a stiffer material such as durometer 75D polyurethane. In this embodiment, like that of the previous ones, the material for theinsulation extension6132 may also be selected to provide a different stiffness than the inner andouter insulation layers6122,6120. For instance, theinsulation extension6132 may also be constructed of a stiffer material such as durometer 75D polyurethane.
• Themetal connector6131 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connector6131 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 36 shows one example of a set of steps that create thelap joint6150 ofFIG. 35. Initially, a structure including theinner insulation layer6122,outer insulation layer6120, andshield6118 may be provided. Theshield6118 has been braided over theinner insulation layer6122 and then theouter insulation layer6120 has been positioned and reflowed or otherwise bonded over theinner insulation layer6122 and theshield6118. To begin construction of thelead6108 and the lap joint6150, the structure is cut to size by making a cut through the insulation layers6120,6122 and theshield6118 at acutting step6154. For a lap joint6130, this first cut is perpendicular to the axial dimension to create a blunt end.
• Once cut to size, theouter insulation layer6120 is then ablated by some distance to expose theshield6118 and theinner insulation layer6122 at anablating step6156. Ablation may be done using tools such as an excimer laser which can very precisely ablate to expose theshield6118. The length of theouter insulation layer6120 to be ablated is sufficient to allow for themetal connector6131 as well as the amount of the replacementouter insulation layer6152 that laps onto theinner insulation layer6122. This length of ablation of theouter insulation layer6120 may vary but an illustrative range is from 0.25 centimeters (cm) to 5 cm.
• Once ablation is complete, themetal connector6131 may then be put in position over theinner insulation layer6122 andshield6118. Themetal connector6131 is crimped or welded to theshield6118 while abutting the end of theouter insulation layer6120 at a crimpingstep6158.
• Once themetal connector6131 is installed, the next step may vary. The replacementouter insulation layer6152 may be installed in various manners such as by reflowing tubing or by injection molding. If by injection molding, then the next step may be either a crimpingstep6160 or aninjecting step6164. If by reflowing tubing, then it may be helpful to proceed to the crimpingstep6160 after ablating.
• At the crimpingstep6160, the portion of theshield6118 that is exposed beyond themetal connector6131 is crimped so as to sink down into theinner insulation layer6122. If a ring or other tool is used to crimp theshield6118 into theinner insulation layer6122, the ring or other tool may then be removed. Where the replacementouter insulation layer6152 is being installed as tubing that is reflowed, then the next step istubing step6162. Where the replacementouter insulation layer6152 is being installed by injection molding, then the next step is injectingstep6164.
• At thetubing step6162, the tubing is slid onto theinner insulation layer6122 and over theshield6118 at the area where theouter insulation layer6120 has been removed and where theshield6118 has been crimped down. The tubing extends beyond the end of theinner insulation layer6122 so that it may eventually be bonded to theinsulation extension6132. The tubing is reflowed or otherwise bonded to theinner insulation layer6122 and to abut the end of themetal connector6131. Contemporaneously, theinsulation extension6132 is bonded in place at the blunt end of theinner insulation layer6122 and to the tubing of the replacementouter insulation layer6152 that extends beyond theinner insulation layer6122 at abonding step6166. This tubing may be reflowed or otherwise bonded onto theinsulation extension6132.
• Returning to the injectingstep6164, in the scenario where the replacementouter insulation layer6152 is to be injection molded, then the injectingstep6164 takes place either after the crimpingstep6158 or after the crimpingstep6160. Material such as the desired polyurethane is injected onto theinner insulation layer6122 and theshield6118 to form the replacementouter insulation layer6152. Contemporaneously, theinsulation extension6132 is bonded to theinner insulation layer6122 and to the replacementouter insulation layer6152 at thebonding step6166.
• Alternative manners of creating the lap joint6150 may also be used. For instance, the structure of theouter insulation layer6120,inner insulation layer6122, andshield6118 may be bonded to theinsulation extension6130 via a butt joint. Then, the area where themetal connector6131 and replacementouter insulation layer6152 will be positioned that is currently occupied by theouter insulation layer6120 is ablated. Theinsulation extension6132 is also ablated at the same or similar depth as theouter insulation layer6120. Themetal connector6131 may then be positioned, and the replacementouter insulation layer6152 may then be injection molded or shrunk into position at the ablation site.
• FIG. 37 shows another embodiment of an implantablemedical lead6108 in cross-section with a cut taken down an axial centerline. Thelead6108 includes a joint between theinner insulation layer6122 and theinsulation extension6132 where theinner insulation layer6122 and theshield6118 terminate. Aninner metal connector6172 is positioned around the inner insulation layer and anouter metal connector6174 is positioned around theinner metal connector6172. A portion of theshield6118 is located between theinner metal connector6172 and theouter metal connector6174 such that a robust physical and electrical connection is established to theshield6118.
• In this example, theshield6118 is braided after theinner metal connector6172 has been positioned so that the braid of theshield6118 laps over theinner metal connector6172. Theouter insulation layer6120 terminates short of the end of theshield6118 andinner insulation layer6122. This may be achieved by ablating theouter insulation layer6120 where it has been previously extruded over the shield andinner metal connector6172.
• As shown in this example, theshield6118 terminates between themetal connectors6172,6174 rather than farther back within the jacket formed by the inner andouter insulation layers6122,6120. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• Themetal connectors6172,6174 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connectors6172,6174 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above forconnector ring6131.
• FIG. 38 shows an alternative manner of attaching the outer metal connector. Rather than ablate theouter insulation layer6120 at the area where theshield6118 andinner metal connector6172 are located, anouter metal connector6176 having features such as teeth that can penetrate through theouter insulation layer6120 is used. Theouter metal connector6176 is crimped in place so that the features penetrate through theouter insulation layer6120 to reach theshield6118 and theinner metal connector6172 and establish the physical and electrical connection.
• FIG. 39 shows a similar embodiment to that ofFIG. 37 where the lead includes theinner metal connector6172 and theouter metal connector6174. However, in this example, theshield6118 does not terminate between themetal connectors6172,6174 but aportion6119 of theshield6118 continues beyond thoseconnectors6172,6174 to extend over the remaining portion of theinner insulation layer6122. Thisportion6119 of theshield6118 may be crimped into a sunken position within theinner insulation layer6122.
• A replacementouter insulation layer6152 may be bonded over theportion6119 of theshield6118 to form a lap joint. Theinsulation extension6132 may then be bonded to theinner insulation layer6122 and the replacementouter insulation layer6152. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• Themetal connectors6172,6174 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connectors6172,6174 as well as any portion of theshield6118 extending beyond themetal connectors6172,6174 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 40 shows a similar embodiment to that ofFIG. 37 where the lead includes theinner metal connector6172 and theouter metal connector6174. However, in this example, theinner metal connector6172 does not wrap around the outside of theinner insulation layer6122 but instead is embedded within theinner insulation layer6122 so as to provide a flush surface for theshield6118 to be braided upon. Theshield6118 is located between thisinner metal connector6172 and theouter metal connector6174. In this example, themetal connectors6172,6174 together with theinner insulation layer6122 form a butt joint with theinsulation extension6132.
• Theinsulation extension6132 is bonded to theinner insulation layer6122 and abuts themetal connectors6172,6174. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• Themetal connectors6172,6174 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connectors6172,6174 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 41 shows one example of a set of steps that create the shield termination ofFIGS. 37-40. Theinner metal connector6172 is positioned on theinner insulation layer6122 or embedded at the end at aconnector step6182. Theshield6118 is braided onto theinner insulation layer6122 and over theinner metal connector6172 at abraiding step6184. Theouter insulation layer6120 is bonded by reflow or another process onto theinner insulation layer6122 over theshield6118 and over theinner metal connector6172 such as by areflowing step6186.
• At this point, preparation is made for theouter metal connector6174. In one example, the outer insulation layer is ablated at anablating step6188 and then the outer metal connector is crimped or welded onto the exposedshield6118 at the overlap to theinner metal connector6172 at a crimpingstep6190. Alternatively, theinner metal connector6176 having the sharp features is crimped onto theouter insulation layer6120 with the sharp features penetrating to theshield6118 and theinner metal connector6172 at a crimpingstep6192. Theinsulation extension6132 is then bonded to theinner insulation layer6122 at abonding step6194.
• FIG. 42 shows a similar embodiment to that ofFIG. 37 where the lead includes theinner metal connector6172 and theouter metal connector6174. However, in this example, theinner metal connector6172 does not wrap around the outside of theinner insulation layer6122 prior to theshield6118 being braided. Instead, theshield6118 is braided over theinner insulation layer6122 and theinner metal connector6172 is then crimped or welded onto theshield6118. Theshield6118 may be sunken into theinner insulation layer6122 in the area where theinner metal connector6172 is positioned.
• Theshield6118 inverts as a whole at aninversion6123 so that aportion6121 of theshield6118 laps over theinner metal connector6172. Theouter metal connector6174 may then be crimped or welded in placed about theportion6121 and theinner metal connector6172. A robust electrical and physical termination of theshield6118 occurs between themetal connectors6172,6174. Theinversion6123 may provide additional benefits for theshield6118, such as reducing any RF energy leakage that might otherwise occur at a blunt end of theshield6118.
• Theinsulation extension6132 is bonded to theinner insulation layer6122 and abuts themetal connectors6172,6174. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• Themetal connectors6172,6174 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connectors6172,6174 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 43 shows one example of a set of steps that create the shield termination ofFIG. 42. Theouter insulation layer6120,inner insulation layer6122, andshield6118 are cut to form a blunt end at acutting step6202. A portion of theouter insulation layer6120 is then ablated to reveal theshield6118 andinner insulation layer6122 at anablating step6204. Theinner metal connector6172 is positioned on theshield6118 and around theinner insulation layer6122 with a portion of theshield6118 and theinner insulation layer6122 extending beyond themetal connector6172 at aconnector step6206. Theshield6118 is inverted as a whole and lapped onto the inner metal connector at afolding step6208.
• At this point, the outer metal connector is crimped or welded onto the exposedshield6118 at the overlap to theinner metal connector6172 at a crimping step6210. Alternatively, theouter metal connector6176 having the sharp features is crimped onto theouter insulation layer6120 with the sharp features penetrating to theshield6118 and theinner metal connector6172. Theinsulation extension6132 is then bonded to theinner insulation layer6122 at abonding step6212.
• FIG. 44 shows another embodiment of an implantablemedical lead6108 in cross-section with a cut taken down an axial centerline. Thelead6108 includes a joint between theinner insulation layer6122 and theinsulation extension6132 where theinner insulation layer6122 terminates. In this example, theshield6118 does not remain braided upon theinner insulation layer6122. Instead, ametal connector6131 is positioned on theinner insulation layer6122 and a portion6125 of theshield6118 is braided onto themetal connector6131. Theouter insulation layer6120 is positioned over thebraid6118 up to themetal connector6131 where thebraid6118 exits theouter insulation layer6120 when lapping onto themetal connector6131.
• The portion6125 may be exposed outside of thelead6108 as a result of lapping onto themetal connector6131. However, for embodiments where themetal connector6131 is for insertion into theheader6106 of theIMD6102, the exposure may occur immediately at the exit to theheader6106 or nearby the header seal. To the extent tissue in-growth is to be avoided in that area, an insulation ring6216 of material the same as or similar to theouter insulation layer6120 may be reflowed or otherwise bonded over the portion6125.
• As shown in this example, a replacementouter insulation layer6152 may be present to form a lap joint between theinner insulation layer6122 and theinsulation extension6132. Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• Themetal connector6131 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of themetal connector6131 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 45 shows one example of a set of steps that create the shield termination ofFIG. 44. Themetal connector6131 is positioned on theinner insulation layer6122 at aconnector step6220. Theshield6118 is braided onto theinner insulation layer6122 and over themetal connector6131 at abraiding step6222. Theouter insulation layer6120 is bonded by reflow or another process onto theinner insulation layer6122 over theshield6118 up to themetal connector6131 such as by areflowing step6224. The insulation ring6216 may then be reflowed or injection molded over the braid portion6125 on themetal connector6131 at abonding step6226.
• FIG. 46 shows another embodiment of an implantablemedical lead6108 in cross-section with a cut taken down an axial centerline. Thelead6108 includes a joint between theinner insulation layer6122 and theinsulation extension6132 where theinner insulation layer6122 terminates. In this example, theshield6118 does not remain braided upon theinner insulation layer6122. Instead, a tapered ablation is created through theouter insulation layer6120 andinner insulation layer6122 and theshield6118 exits theouter insulation layer6120 and separates from theinner insulation layer6122 at the taper.
• A metal connector6232 with a threaded taper6234 is threaded onto the taper of the inner andouter insulation layers6122,6120. The threaded taper6234 bites into the inner andouter insulation layers6122,6120 to provide a sturdy physical connection. Theshield6118 passes through the metal connector6232 to an opposite side where an opposite taper is present. There, theshield6118 terminates while being positioned firmly between the taper of the metal connector6232 and a taper of an inner metal connector6236 that is positioned about theinsulation extension6132.
• Theinsulation extension6132 in this example extends the remainder of thelead6108 wherering connectors6134 are located at the proximal end. Thefilars6124 jumper to their respective ring connectors via afilar jumper6136. The lumen may be present in some embodiments with thefilars6124 being located about the lumen.
• The metal connectors6232,6236 may be included on either the proximal or distal end to terminate theshield6118 as discussed above. The separation of the metal connectors6232,6236 to the distal electrode or proximal connector ring may also be in accordance with the separation as discussed above.
• FIG. 47 shows one example of a set of steps that create the shield termination ofFIG. 46. The inner metal connector6236 is positioned at the end of theinner insulation layer6122 at aconnector step6242. Theshield6118 is braided onto theinner insulation layer6122 and over the inner metal connector6236 at abraiding step6244. Theouter insulation layer6120 is bonded by reflow or another process onto theinner insulation layer6122 over theshield6118 such as by areflowing step6246.
• The inner andouter insulation layers6122,6120 are ablated to form the taper and expose theshield6118 at anablating step6248. The outer metal connector6232 is then placed into position over the inner metal connector6236 and the taper of the inner andouter insulation layers6122,6120 at aconnector step6250. Here, the outer metal connector6232 may be turned relative to the inner andouter insulation layers6122,6120 to sink the threaded taper6234 into the inner andouter insulation layers6122,6120 while the outer metal connector6232 firmly contacts theshield6118 positioned against the inner metal connector6236. The outer metal connector6232 may be crimped or welded into place over theshield6118 and the inner metal connector6236.
• FIG. 48 shows an embodiment with an additional feature that may be included for a joint6276, which may be of various types such as the butt, scarf, orlap joints6130,6140, and6150. At the joint6276, theouter metal connector6131,6174 of thelead6108 encounters anotherlayer6278. Thislayer6278 may be theinsulation extension6132 and/or the replacementouter insulation layer6152. In either case, wires of theshield6118 may partially extend into thelayer6278. However, prior to bonding thelayer6278 to thelayer6122, the ends of the wires of theshield6118 may be individually folded over atareas6274 as shown inFIG. 48. In this manner, the folded over ends are less likely to fray and migrate.
• Embodiments as disclosed in relation toFIGS. 49-58 provide for rotation of a stylet within a lumen of an implantable medical lead by applying rotation directly to the implantable medical lead. The implantable medical lead has torsional stiffness and is rotationally coupled to the stylet. The torsional stiffness may be provided by features within the jacket of the lead body, such as a shield. The rotational coupling of the implantable medical lead to the stylet may be provided via features of the lead and/or stylet.
• FIG. 49 shows a scenario where an implantablemedical lead7108 is being implanted within a patient. Thelead7108 enters the patient at anintroduction site7112 where an introduction needle provides a passageway into the body. Thelead7108 is shown transparently for purposes of illustration to reveal astylet7132 present within a lumen of thelead7108. Thestylet7132, and specifically thebent tip7134 of thestylet7132, is used to steer thelead7108 as thelead7108 is being inserted in order to direct the distal end of thelead7108 to the stimulation site which may be a significant distance from theintroduction site7112.
• Thebent tip7134 is rotated in position by thestylet7132 being rotated. Thestylet7132 may include astylet hub7130 on the proximal end. Thisstylet hub7130 may engage thelead7108 as discussed below. To rotate thestylet7132 and thebent tip7134, the doctor may applyrotation7136 directly to thelead7108 at theintroduction site7112 rather than reaching back to grasp thestylet hub7130. Thelead7108 is torsionally stiff such that therotation7136 causes rotation along the length of thelead7108 includingrotation7138 near the proximal end,rotation7142 of the hub, androtation7140 near the distal end.
• Thestylet7132 is rotationally coupled to thelead7108 at one or more points. The rotational coupling may be near the proximal end or the distal end of thelead7108, and this rotational coupling may be done in various ways as described below. Thus, therotation7136 being applied to thelead7108 at theintroduction site7112 causes thestylet7132 to rotate along the length to thebent tip7134.
• Thestylet7132 andstylet hub7130 may be constructed of various materials. For example, the stylet may be constructed of steel, stainless steel, tungsten, beryllium, and their alloys which provides torsional rigidity. The stylet hub may be constructed of various materials such as nylon, polycarbonate, or other rigid engineering plastics.
• FIG. 50 shows an implantable medical system in place once thelead7108 has been directed to the stimulation site. The implantable medical system includes anIMD7102 having a biocompatible case and aheader7106. Thelead7108 includesdistal electrodes7116 at the stimulation site that are used to provide the stimulation. The lead also includesproximal connectors7110 that are fixed by a set screw or other mechanism within theheader7106 and are connected to electrical circuitry of theIMD7102. TheIMD7102 produces stimulation signals that are provided to theconnectors7110. Filars within thelead7108 carry the stimulation signals from theconnectors7110 to theelectrodes7116.
• FIGS. 51 and 52 show an embodiment of the implantablemedical lead7108 where ashield7118 is present that provides the torsional rigidity. Anouter jacket layer7120 is shown transparently inFIG. 51 for purposes of illustrating theshield7118. Theshield7118 may be included for various reasons in addition to creating the torsional rigidity. For example, theshield7118 may provide protection from unwanted RF energy. For instance, thelead7108 may be a magnetic resonance imaging (MRI) safe lead that allows the patient to have an MRI scan without risking tissue damage due to induced RF currents in the filars of thelead7108. Theconductive filars7124 extend the length of thelead7108 and interconnect theproximal connectors7110 to thedistal electrodes7116 so that stimulation signals are conducted from the proximal end to the distal end of thelead7108.
• As shown inFIG. 51, theshield7118 of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, platinum, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield7118, particularly for embodiments where a portion of theshield7118 may be exposed for purposes of grounding. While theshield7118 is shown as a braid, other shield configurations may be chosen such as a metal foil that is wrapped in an overlapping fashion. If shielding is not desired, then the foil may be more loosely wrapped and still provide torsional rigidity.
• As shown inFIG. 52, theshield7118 may be embedded within the jacket of thelead7108. One manner of constructing thelead7108 with theshield7118 is to provide aninner jacket7122 that encloses thefilars7124 and anyadditional insulation layer7126 that may surround each filar7124. Theshield7118 may then reside on the outer portion of theinner jacket7122, and theouter jacket7120 may then enclose theshield7118.
• Theshield7118 may ground to tissue via an RF coupling through theouter layer7120 and/or via grounding to thecan7104 and/or to the tissue via ground rings. For embodiments where it is desirable for theshield7118 to RF couple to tissue, theouter jacket layer7120 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield7118 grounds at the can of the IMD and grounding via a RF coupling from theshield7118 through theouter jacket7120 directly to the tissue is of less significance, then theshield7118 may be located further from the outer surface of thelead7108. Theouter jacket7120 may be added over theshield7118 by shrinking in place or by being extruded over theshield7118.
• The inner andouter jackets7122,7120 may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. Thelumen7128 is included in theinner jacket7122, particularly for percutaneous leads7108, to allow thestylet7132 to be inserted for purposes of pushing and steering the lead into the desired position within the patient.
• As shown in the cross-section ofFIG. 52, at this particular point along the lead thestylet7132 is free within thelumen7128. Thestylet7132 has clearance relative to thelumen7128. This clearance may aid in the insertion of thestylet7132 into thelumen7128.
• FIG. 53 shows a cross-section at a point along an embodiment of thelead7108 where a rotational coupling is established between thelead7108 and thestylet7132. At this point, thelumen7128 of thelead7108 has a portion forming apassageway7144 that has a square cross-sectional shape rather than being round. As one example, thispassageway7144 may be created in the distal tip of thelead7108, distal to the location of the distal electrodes. Thestylet7132 likewise has ashaft7146 that has a square cross-sectional shape and that fits within the square shapedpassageway7144 of thelumen7128. The position of the square shapedpassageway7144 may be such that when thestylet7132 is fully inserted in thelead7108, the square shapedshaft7146 of thestylet7132 mates to the square shapedpassageway7144 of thelumen7128. The square shape effectively keys thestylet7132 to thelead7108 so that a rotational coupling is achieved.
• FIG. 54 shows a cross-section at a point along another embodiment of thelead7108 where a rotational coupling is established between thelead7108 and thestylet7132. At this point, thelumen7128 of the lead has a particular portion forming apassageway7148 that has a star cross-sectional shape rather than being round. As one example, thispassageway7148 may be created in the distal tip of thelead7108, distal to the location of the distal electrodes. Thestylet7132 likewise has ashaft7150 that has a star cross-sectional shape and that fits within the star shapedpassageway7148 of thelumen7128. The position of the star shapedpassageway7148 may be such that when thestylet7132 is fully inserted in thelead7108, the star shapedshaft7150 of thestylet7132 mates to the star shapedpassageway7148 of thelumen7128. The star shape effectively keys thestylet7132 to thelead7108 so that a rotational coupling is achieved.
• FIG. 55 shows a cross-section at a point along another embodiment of thelead7108 where a rotational coupling is established between thelead7108 and thestylet7132. At this point, thelumen7128 of the lead has a particular portion forming apassageway7152 that has a hexagonal cross-sectional shape rather than being round. As one example, thispassageway7152 may be created in the distal tip of thelead7108, distal to the location of the distal electrodes. Thestylet7132 likewise has ashaft7154 that has a hexagonal cross-sectional shape and that fits within the hexagonal shapedpassageway7152 of thelumen7128. The position of the hexagonal shapedpassageway7152 may be such that when thestylet7132 is fully inserted in thelead7108, the hexagonal shapedshaft7154 of thestylet7132 mates to the hexagonal shapedpassageway7152 of thelumen7128. The hexagonal shape effectively keys thestylet7132 to thelead7108 so that a rotational coupling is achieved.
• The square, star, and hexagonal shapes are shown for purposes of illustration. It will be appreciated that any number of shaped engagements may be utilized to establish a rotational coupling between thelead7108 and thestylet7132. Furthermore, it will be appreciated that the coupling may occur at any point or multiple points along thelead7108 where the torsional stiffness is present
• FIG. 56 shows a side view of a proximal end of thelead7108 with thelumen7128 engaging an embodiment of thestylet hub7130 in order to establish a rotational coupling between thestylet7132 and thelead7108. Thestylet hub7130 includes a taperedregion7156 that extends from thehub7130 to thestylet7132. Thistapered region7156 at a large diameter end has a diameter larger than that of thelumen7128. As a result, the taperedregion7156 may be press fit into thelumen7128 of thelead7108 in order to produce a frictional fit that establishes a rotational coupling.
• FIG. 57 shows a side view of a proximal end of thelead7108 with thelumen7128 engaging another embodiment of thestylet hub7130 in order to establish a rotational coupling between thestylet7132 and thelead7108. Thestylet hub7130 includes asplined region7158 that extends from thehub7130 to thestylet7132. The diameter created by thesplined region7158 may be greater than the diameter of thelumen7128. Thissplined region7158 may be press fit into thelumen7128 of thelead7108 in order to engage the splines with thelumen7128 to establish a rotational coupling.
• FIG. 58 shows a side view of a proximal end of thelead7108 with thelumen7128 engaging another embodiment of thestylet hub7130 in order to establish a rotational coupling between thestylet7132 and thelead7108. Thestylet hub7130 includes a threadedregion7160 that extends from thehub7130 to thestylet7132. The diameter created by the threadedregion7160 may be greater than the diameter of thelumen7128. This threadedregion7160 may be screwed into thelumen7128 of thelead7108 in order to engage the threads with thelumen7128 to establish a rotational coupling.
• The tapered, splined, and threaded engagements of thehub7130 to thelumen7128 are shown for purposes of illustration. It will be appreciated that any number of hub features may be used to engage thelumen7128 to provide the rotational coupling. It will be further appreciated that similar features may be used to allow thehub7130 to instead engage theouter layer7120 of thelead7108 at the proximal end such as by having a taper, splines, or threads that surround theouter layer7120 but with a smaller diameter than theouter layer7120. These features face inward to engage theouter layer7120 and establish the rotational coupling.
• Embodiments as disclosed in relation toFIGS. 59-72 provide radiopaque markers that are added to implantable medical leads or to implantable medical devices (IMD) connected to the leads to identify the leads as being designed for safe application of a medical procedure such as an MRI scan. The radiopaque markers arc visible on an X-ray or during fluoroscopy so that administering personnel can have a visual assurance that the lead is designed for safe application of the medical procedure of interest.
• FIG. 59 shows an embodiment of an implantable medical system that includes anIMD8102 having a can8104 that houses electronics and aheader8106. In this example, theIMD8102 provides signals to a pair of implantablemedical leads8108,8109 which are physically and electrically connected to theIMD8102 via theheader8106.
• Radiopaque markers8130,8131 are provided to identify theleads8108,8109 as being safe for a given procedure. In this particular example, theradiopaque markers8130,8131 are tags that are fixed directly tocorresponding leads8108,8109.Sutures8132 of the permanent type hold thetag8130 to thelead8108 whilesutures8133 hold thetag8131 to thelead8109. By individually tagging bothleads8108,8109, the administering personnel can be assured that both leads are safe for the given procedure.
• Thetags8130,8131 may be added after theleads8108,8109 have been successfully implanted into the patient. For percutaneous leads, this is particularly desirable because thelead8108,8109 is inserted into the body of the patient via an introducer needle that lacks clearance for thetags8130,8131. Thus, once theleads8108,8109 are in position with the proximal ends of the leads being near the incision site and with the introducer needle removed, thetags8130,8131 can be inserted into a pocket made for theIMD8102 and sutured in place by the doctor.
• Thetags8130,8131 may be constructed of a biocompatible material that has a density that is adequately radiopaque by being visible on an X-ray or during fluoroscopy. Examples of such materials include barium, tantalum, platinum, and platinum-iridium. The size of thetags8130,8131 may vary but when sized to have a length and width in the range of 0.25 to 5 centimeters and 0.01 to 0.2 inch thickness, thetag8130,8131 is adequately visible while being small enough to comfortably fit within or nearby the pocket near theIMD8102.
• When administering personnel wish to perform a given medical procedure such as an MRI, the personnel may take an X-ray or conduct fluoroscopy to look for the radiopaque marker. TheIMD8102 itself may need to also be designed for safety during a given medical procedure and may have its own internal or external radiopaque marker. Thus, placing thetags8130,8131 nearby theIMD8102 may be desirable so that the tags of both theleads8108,8109 and the marker of theIMD8102 arc in the same field of view of an X-ray or during fluoroscopy.
• In this example ofFIG. 59, thetags8130,8131 include anaperture8138,8139 in the shape of a particular symbol. Due to theaperture8138,8139, this shape within thetag8130,8131 is visibly distinguishable on the X-ray or during fluoroscopy. Thus, thisaperture8138,8139 may identify the safety aspects of thelead8108,8109 and/or the medical procedures that are safe to conduct. The shape of theapertures8138,8139 inFIG. 59 is a wave that represents that theleads8108,8109 are safe for an MRI scan conducted within normal operating parameters.
• FIG. 60 shows a similar configuration for theradiopaque tag8130. However, rather than the doctor suturing thetag8130 to thelead8108, the doctor connects the proximal end of thelead8108 to theIMD8102 that is placed into the pocket and sutures thetag8130 to theIMD8102. In the example shown,sutures8132 extending from thetag8130 are tied around thecan8104. It will be appreciated that thesutures8132 could be tied to theIMD8102 in other ways or to designated features of theIMD8102.
• FIG. 61 shows another example of placing thetag8130 in close proximity to theIMD8102 and lead8108. However, in this example, thetag8130 is not tied to either but is instead left loosely positioned within thepocket8136 where theIMD8102 is positioned. Thepocket8136 prevents thetag8130 from migrating away from the position of theIMD8102 so that thetag8130 remains in the same field of view as theIMD8102 and lead8108 during an X-ray or fluoroscopy.
• FIG. 62 shows another example of placing thetag8130 in close proximity to theIMD8102 and thelead8108. In this example, rather than suturing thetag8130 to thelead8108, the doctor may have chosen to bond thetag8130 to the lead using aglue8140. Examples of a glue suitable for bonding thetag8130 to thelead8108 include medical adhesives.
• FIG. 63 shows another example of placing thetag8130 in direct proximity of theIMD8102 by bonding thetag8130 to theIMD8102. Here, thetag8130 is bonded to theIMD8102 with theglue8140. Examples of a glue suitable for bonding thetag8130 to theIMD8102 also include medical adhesives.
• FIG. 64 shows another example of placing thetag8130 in close proximity to theIMD8102 and thelead8108. In this example, thetag8130 is attached to aclamp8142, such as a U-shaped spring-loaded clamp or other clamp structures such as features that mechanically lock including detents. Theclamp8142 tightens against thelead8108 to hold thetag8130 in position relative to thelead8108.
• FIG. 65 shows another example of placing thetag8130 in direct proximity to theIMD8102. Here, thetag8130 includes theclamp8142 which is tightened against thecan8104 of theIMD8102. Theclamp8142 could tighten against other portions of theIMD8102 as well such as theheader8106. Theclamp8142 ofFIG. 65 may be of the same types discussed above in relation toFIG. 64.
• FIG. 66 shows another example of placing thetag8130 in close proximity to theIMD8102 and thelead8108. In this example, thetag8130 has anextension8144 that forms a ring shape. Initially, theextension8144 may be an open ring so that it easily fits onto thelead8108. Theextension8144 may then be crimped to form a closed or nearly closed ring about thelead8108 and to fix thetag8130 relative to thelead8108.
• FIG. 67A shows an example of a radiopaque marker being installed on a lead where the radiopaque marker is not a tag. Instead, the radiopaque marker is aradiopaque coil8146′ that is in a radially expanded state produced by axially compressing thecoil8146′. The radially expanded state allows thecoil8146′ to be placed about thelead8108, with thelead8108 traveling through the center of the coil in an axial direction. Thecoil8146′ is placed onto the proximal end of thelead8108, shown here withconnectors8110, prior to the proximal end being inserted into theheader8106.
• FIG. 67B shows theradiopaque coil8146 in a radially contracted state. Here, once properly positioned along thelead8108, thecoil8146 has been allowed to naturally expand axially to radially contract until the coil diameter meets that of thelead8108 to fix thecoil8146 in place on thelead8108. Thelead8108 is then connected to theIMD8102, with thecoil8146 being located in proximity to theIMD8102 in this example so as to be in the same field of view. Thecoil8146 itself is the visible shape that indicates that thelead8108 is safe for a particular medical procedure such as an MRI.
• Theradiopaque coil8146 may be constructed of materials similar to thetag8130. For instance, thecoil8146 may be constructed of barium, tantalum, platinum, and platinum-iridium. The size of thecoil8146 may vary but when sized in the range of 0.04 inch to 1.0 inch in length and from 2 mils to 0.10 inch in diameter when radially contracted, thecoil8146 is adequately visible while being small enough to comfortably fit within or nearby the pocket near theIMD8102.
• FIGS. 68A and 68B show an example of atool8150 being used to place thecoil8146′ in the radially expanded state onto thelead8108 and to deposit thecoil8146 in the radially contracted state at the desired position on thelead8108. Thetool8150 holds thecoil8146′ in the radially expanded state by providing a larger diameter than thelead8108 and while providing a passageway for thelead8108.
• As shown inFIG. 68B, thetool8150 is positioned on thelead8108 with thelead8108 passing through the passageway of thetool8150. Thecoil8146′ is pushed off of thetool8150 until thecoil8146 has a radially contracted end about thelead8108. Thetool8150 may then be pulled away from thelead8108 to allow the remainder of thecoil8146′ in the radially expanded state to slide off of thetool8150 and onto thelead8108 where thecoil8146 achieves the radially contracted state.
• FIG. 69A shows apolymer structure8152 that may be used to place a radiopaque marker onto thelead8108.FIG. 69B shows thepolymer structure8152 once positioned on thelead8108. Thispolymer structure8152 includes acylindrical aperture8154 that allows thelead8108 to pass through. Thecylindrical aperture8154 may stretch to a larger diameter than thelead8108 such as by using a conventional anchor deployment tool to position the polymer structure onto thelead8108. Thepolymer structure8152 may then be removed from the anchor tool to allow thepolymer structure8152 to contract onto thelead8108.
• Thepolymer structure8152 includes an offsetportion8155. Within this offsetportion8155, aradiopaque plate8156 is embedded. Theradiopaque plate8156 may include asymbol8158 or other information to be conveyed to administering personnel. Theradiopaque plate8156 may be constructed of materials similar to thetag8130. For instance, theplate8156 may be constructed of barium, tantalum, platinum, and platinum-iridium. The size of theplate8156 may vary but when sized in at about 0.040 inch in length/width and about 0.01 to 0.2 inch thick, theplate8156 is adequately visible while being small enough to be contained within thepolymer structure8152.
• Thepolymer structure8152 ofFIGS. 69A and 69B is similar to a lead anchor. However, thispolymer structure8152 lacks suture wings. Because the contraction of thecylindrical aperture8154 holds the polymer structure in place, no sutures are needed.
• The offset of theportion8155 where theradiopaque plate8156 is located provides for ease of removal of thepolymer structure8152 from thelead8108. An axial cut can be made along thecylindrical aperture8154 because the radiopaque marker does not surround thecylindrical aperture8154. However, if ease of removal is not of concern, then embodiments may provide theradiopaque plate8156 centered about thecylindrical aperture8154.
• FIG. 69C shows asimilar polymer structure8168. However, thepolymer structure8168 is in the form of a lead anchor that includessuture wings8170 while also including theradiopaque plate8156. Rather than relying on the cylindrical aperture to contract onto thelead8108, thelead anchor8168 may additionally or alternatively havesutures8132 that tie thesuture wings8170 to thelead8108 to hold thepolymer structure8168 in place in proximity to theIMD8102. Theradiopaque plate8156 may be centered about thelead8108 within thepolymer structure8160 even where ease of removal is desired if thepolymer structure8160 is held in place by thesutures8132 rather than a contracted state upon thelead8108.
• FIG. 70A shows anotherpolymer structure8160 that may be used to place a radiopaque marker onto thelead8108.FIG. 70B shows thepolymer structure8160 once positioned on thelead8108. Thispolymer structure8160 includes acylindrical aperture8162 that allows thelead8108 to pass through. Thecylindrical aperture8162 may stretch to a larger diameter than thelead8108 such as by using a conventional anchor deployment tool to position thepolymer structure8160 onto thelead8108. Thepolymer structure8160 may then be removed from the anchor tool to allow thepolymer structure8160 to contract onto thelead8108.
• Thepolymer structure8160 includes an offsetportion8164. Within this offsetportion8164, aradiopaque coil8166 is embedded. Theradiopaque coil8166 may form a symbol or other information to be conveyed to administering personnel. Theradiopaque coil8166 may be constructed of materials similar to thecoil8146. For instance, thecoil8166 may be constructed of barium, tantalum, platinum, and platinum-iridium. The size of thecoil8166 may vary but when sized in the range of 0.04 to 1.0 inch in length and 2 mils to 0.10 inch in wire diameter with an overall diameter of 0.020 to 0.5 inch, thecoil8166 is adequately visible while being small enough to be contained within thepolymer structure8160.
• Thepolymer structure8160 ofFIGS. 70A and 70B is also similar to a lead anchor. However, thispolymer structure8160 lacks suture wings. Because the contraction of thecylindrical aperture8162 holds thepolymer structure8160 in place, no sutures are needed.
• The offset of theportion8164 where theradiopaque coil8166 is located provides for ease of removal of thepolymer structure8160 from thelead8108. An axial cut can be made along thecylindrical aperture8162 because the radiopaque marker does not surround thecylindrical aperture8162. However, if ease of removal is not of concern, then embodiments may provide theradiopaque coil8166 centered about thecylindrical aperture8162.
• FIG. 70C shows asimilar polymer structure8172. However, thepolymer structure8172 is in the form of a lead anchor that includessuture wings8174 while also including theradiopaque coil8166. Rather than relying on the cylindrical aperture to contract onto thelead8108, thelead anchor8172 may additionally or alternatively havesutures8132 that tie thesuture wings8174 to thelead8108 to hold thepolymer structure8172 in place in proximity to theIMD8102. Theradiopaque coil8166 may be centered about the lead within thepolymer structure8172 even where case of removal is desired if thepolymer structure8172 is held in place by thesutures8132 rather than a contracted state upon thelead8108.
• FIGS. 71 and 72 show an embodiment of the implantablemedical lead8108 where ashield8118 is present. Thisshield8118 may provide protection from RF energy that allows thelead8108 to be conditionally MRI safe and thus eligible to carry the radiopaque marker for an MRI. Anouter jacket layer8120 is shown transparently inFIG. 71 for purposes of illustrating theshield8118. Theshield8118 may provide protection from RF energy of an MRI that might otherwise cause tissue damage due to induced RF currents in the filars of thelead8108. Theconductive filars8124 extend the length of thelead8108 and interconnect theproximal connectors8110 to the distal electrodes so that stimulation signals are conducted from the proximal end to the distal end of thelead8108.
• As shown inFIG. 71, theshield8118 of this example is a braided metal wire. The metal wire may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield8118, particularly for embodiments where a portion of theshield8118 may be exposed for purposes of grounding. While theshield8118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead8108 in an overlapping manner or anouter layer8120 that is heavily doped with conductive particles.
• As shown inFIG. 72, theshield8118 may be embedded within the jacket of thelead8108. One manner of constructing thelead8108 with theshield8118 is to provide aninner jacket8122 that encloses thefilars8124 and anyadditional insulation layer8126 that may surround each filar8124. Theshield8118 may then reside on the outer portion of theinner jacket8122, and theouter jacket8120 may then enclose theshield8118.
• Theshield8118 may ground to tissue via an RF coupling through theouter layer8120 and/or via grounding to thecan8104 and/or to the tissue via ground rings. For embodiments where it is desirable for theshield8118 to RF couple to tissue, theouter jacket layer8120 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield8118 grounds at thecan8104 of theIMD8102 and grounding via a RF coupling from theshield8118 through theouter jacket8120 directly to the tissue is of less significance, then theshield8118 may be located further from the outer surface of thelead8108. Theouter jacket8120 may be added over theshield8118 by shrinking in place or by being extruded over theshield8118.
• The inner andouter jackets8122,8120 may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. Alumen8128 may be included inside of theinner jacket8122 around which theinsulated filars8124 are coiled or otherwise positioned. Thelumen8128 may be useful, particularly for percutaneous leads8108, to allow a stylet to be inserted for purposes of pushing and steering thelead8108 into the desired position within the patient.
• Embodiments as disclosed in relation toFIGS. 73-76D provide for reduced torsional stiffness of a shield present within an implantable medical lead for use with an implantable medical device (IMD). The torsional stiffness of the shield may be reduced in various ways such as by axially cutting the shield to form a slot that breaks the circumferential mechanical continuity of the shield. The slot may then be closed to re-establish the circumferential shielding continuity of the shield and to preserve the shielding function.
• FIG. 73 shows an example of an implantablemedical system9100 that includes anIMD9102 coupled to alead9108. TheIMD9102 includes ametal can9104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD9102 includes aheader9106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can9104. Theheader9106 is shown transparently for purposes of illustration. Theheader9106 provides a structure for securing thelead9108 to theIMD9102 and for establishing electrical connectivity between circuitry of theIMD9102 and electrodes of thelead9108.
• Thelead9108 includeselectrodes9116 on a distal end that are positioned at a stimulation site within a patient. The lead also includes connector rings9110 on a proximal end that is positioned within theheader9106. The connector rings9110 make physical contact withelectrical connections9111 within the header. Theelectrical connections9111 may include a metal contact that theconnector ring9110 rests against upon being inserted into theheader9106 where a wire extends from the metal contact into thecan9104 where the circuitry is housed. Signals applied by theIMD9102 to the connector rings9110 are conducted through thelead9108 to theelectrodes9116 to provide the stimulation therapy to the patient.
• Thelead9108 is secured in theheader9106 such as by aset screw block9112 within theheader9106 that allows at least oneset screw9114 to be tightened against at least one of the connector rings9110. Ashield9118 as shown inFIGS. 74A and 74B may be grounded to the body along one or more points down the length of the lead from theIMD9102 via capacitive coupling through the jacket or via ground rings. Theshield9118 may also be grounded at thecan9104 of theIMD9102 ofFIG. 73.
• FIGS. 74A and 75A show an example of thelead9108, where ashield9118 is present. Anouter insulation layer9120 of a lead jacket is shown transparently inFIG. 74A for purposes of illustrating theshield9118. Theshield9118 blocks at least some RF energy from directly coupling toconductive filars9124 that are present within thelead9108. Theconductive filars9124 extend the length of the lead and interconnect the proximal connector rings9110 to thedistal electrodes9116 so that stimulation signals are conducted from the proximal end to the distal end of thelead9108.
• As shown inFIG. 74A, theshield9118 of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield9118, particularly for embodiments where a portion of theshield9118 may be exposed for purposes of grounding. While theshield9118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a coiled configuration, foil strip wrapped about thelead9108 in an overlapping manner or anouter layer9120 that is heavily doped with conductive particles.
• As shown inFIG. 75A, theshield9118 may be embedded within the jacket of thelead9108. One manner of constructing thelead9108 with theshield9118 is to provide aninner insulation layer9122 of the jacket that encloses thefilars9124 and anyadditional insulation layer9126, such as polytetrafluoroethylene (PTFE) that may surround each filar9124. Theshield9118 may then reside on the outer portion of theinner insulation layer9122, and theouter insulation layer9120 may then enclose theshield9118. Theouter insulation layer9120 may be added over theshield9118 and shrunk in place or may be extruded over theshield9118. Theouter jacket9120 maybe added over thebraid9118, or it may be extruded over the braid.
• For embodiments where it is desirable for theshield9118 to RF couple to tissue, typically as a capacitive coupling, in addition to grounding at thecan9104 or along thelead9108, the amount of theouter jacket layer9120 covering theshield9118 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield9118 grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, theshield9118 may be located further from the outer surface of thelead9108.
• The inner andouter insulation layers9122,9120 of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. Alumen9128 may be included inside of theinner jacket9122 around which theinsulated filars9124 are coiled or otherwise positioned. Thelumen9128 may be useful, particularly for percutaneous leads9108, to allow a stylet to be inserted for purposes of pushing and steering thelead9108 into the desired position within the patient.
• As shown, theshield9118 has mechanical and shielding continuity about the circumference of theinner insulation layer9122. This continuity is achieved by the wires of thebraided shield9118 being continuous. The circumferential shielding continuity exists because there arc no non-conductive openings large enough to allow RF energy to easily pass through. The mechanical continuity produces a large increase in torsional stiffness over an unshielded lead, which may be beneficial in some respects but is detrimental in other respects.
• The detrimental aspects may include difficulties twisting the lead during implant procedures due to high torsional stiffness. Twisting thelead9108 may be beneficial when guiding thelead9108 to the stimulation site and to theIMD9102 and when wrapping excess lengths of thelead9108 about theIMD9102. Thus, in some instances, it may be desirable to provide a shielded implantable medical lead with reduced torsional stiffness.
• FIGS. 74B and 75B show thelead9108 once theshield9118 has been cut in an axial direction to create aslot9140. Ashield portion9142 creates one edge of theslot9140 while an opposingshield portion9144 creates the opposite edge. Theslot9140 may be created by a single cut or by two cuts that are roughly parallel and result in a section of theshield9118 being removed. Theshield9118 may be cut prior to applying theouter layer9120 so that theouter layer9120 does not need to be cut to cut theshield9118.
• Theshield9118 ofFIG. 74B now lacks the circumferential mechanical continuity due to theslot9140, and the torsional stiffness is reduced considerably as a result. However, theslot9140 also breaks the circumferential shielding continuity because theslot9140 has an axial dimension that allows RF energy to easily pass through theslot9140. Therefore, to preserve the RF shielding function of theshield9118, theslot9140 is closed in one of various ways that re-establishes the circumferential shielding continuity while allowing the circumferential mechanical continuity to remain broken.
• FIGS. 74C and 75C show one embodiment of thelead9108 where theslot9140 is closed to re-establish circumferential shielding continuity by closing the slot sufficiently relative to the wavelengths of RF energy so that the RF energy cannot easily penetrate theshield9118 at the location of theslot9140. In this example, theshield portion9144 laps over theshield portion9142 to close theslot9140 from a shielding continuity standpoint. Theshield portion9144 may or may not contact theshield portion9142 such that circumferential electrical continuity may or may not be re-established. However, either way, theshield portion9144 is not bonded to theshield portion9142 such that they remain mobile with respect to one another, thereby maintaining the break in the circumferential mechanical continuity.
• Theshield portion9144 may be lapped onto theshield portion9142 as a natural result of cutting theshield9118, such as where theshield9118 is loosely braided over theinner insulation layer9122. The loose braiding provides an uncut shield diameter that is slightly larger than the diameter of theinner insulation layer9122 such that cutting theshield9118 to create theslot9140 allows theshield portion9144 to collapse onto theshield portion9142. This collapse of theshield9118 closes theslot9140 while the shield diameter is reduced down to the diameter of theinner insulation layer9122.
• Theouter insulation layer9120 is then added over theshield9118. Theouter insulation layer9120 is a polymer that holds theshield9118 in place against theinner insulation layer9122. However, the polymer of theouter insulation layer9120 is compliant so that theshield portion9144 can move relative to theshield portion9142 upon application of torque to thelead9108.
• FIGS. 74D and 75D show another embodiment of thelead9108 where theslot9140 is closed to re-establish circumferential shielding continuity by closing theslot9140 sufficiently relative to the wavelengths of RF energy so that the RF energy cannot easily penetrate theshield9118 at the location of theslot9140. In this example, theslot9140 is closed by application of ashield patch9146. Theshield patch9146 may be constructed similarly to thebraided shield9118, using the same or similar metal wire.
• In the example shown, theshield patch9146 is a grid pattern, but it will be appreciated that other patterns may also be used such as where the grid includes U-shaped portions along the axial wires so that the U-shaped portions allow for axial extension of thelead9108. Theshield patch9146 overlaps onto theshield9118 on both sides of theslot9140. Theshield portion9144 may or may not contact theshield portion9142 such that circumferential electrical continuity may or may not be re-established. However, either way, theshield patch9146 is not bonded to theshield9118 such that theshield patch9146 can move relative to theshield9118 on either side of theslot9140. As a result, the circumferential mechanical continuity of theshield9118 remains broken.
• Because theshield patch9146 is being added to thelead9108, thebraided shield9118 may be applied to theinner insulation layer9122 in a close fitting manner as opposed to loosely braiding theshield9118. Once the cut is complete, theshield patch9146 may then be placed into position directly onto theshield9118 and across theslot9140.
• Theouter insulation layer9120 is then added over theshield9118 and theshield patch9146. As in the embodiment ofFIGS. 74C and 75C, theouter insulation layer9120 is a polymer, and theouter insulation9120 holds theshield9118 in place against or close to theinner insulation layer9122 and also holds theshield patch9146 in place against or close to theshield9118. However, the polymer of theouter insulation layer9120 is compliant so that theshield patch9146 can move relative to theshield9118 on either or both sides of theslot9140 upon application of an axial twisting moment to thelead9108.
• FIG. 76A shows a representation of ashield9150 that may be used in an implantablemedical lead9108. The representation is a tube, and this tube is illustrative for multiple reasons. Where theshield9150 is a braided shield, such as theshield9118, the apertures are small relative to the wavelengths of the RF energy such that thebraided shield9118 is effectively a tube from the perspective of the RF energy. Where theshield9150 is another configuration, such as a foil strip wrapped around theinner insulation layer9122 in an overlapping fashion, the foil strip forms a true tube. In either case, a linear axial cut in theshield9150 reduces torsional stiffness but appears as theslot9152, which presents an opening that the RF energy may pass through.
• FIG. 76B shows a tubular representation of theshield9150 that may correspond to a braided shield or other shield configuration such as an overlapping wrapped foil strip. Here, theshield9150 uses the overlap technique such as that shown above inFIGS. 74C and 75C to close theslot9152 formed by the linear axial cut. As can be seen, ashield portion9156 on one side of theslot9152 overlaps anothershield portion9154 on the opposite side of theslot9152 and may or may not contact theshield portion9154. Thus, theslot9152 is effectively closed to establish shielding continuity across theslot9152, but theshield portions9154,9156 may move relative to one another so that the mechanical continuity remains broken.
• FIG. 76C shows a tubular representation of theshield9150 that may also correspond to a braided shield or other shield configuration such as an overlapping wrapped foil strip. Here, theshield9150 uses a shield patch technique such as that shown above inFIGS. 74D and 75D to close theslot9152 formed by the linear axial cut. As can be seen, ashield patch9158 reaches across theslot9152 to overlap and may or may not physically contact theshield9150 on both sides of theslot9152. Thus, theslot9152 is effectively closed to establish shielding continuity across theslot9152, but theshield patch9158 may move relative to theshield9150 on either or both sides of theslot9152 so that the mechanical continuity remains broken.
• FIG. 76D shows a tubular representation of theshield9160 that may correspond to a braided shield or other shield configuration such as an overlapping wrapped foil strip. Here, theshield9160 has been cut axially using a helical cut rather than a linear cut to create ahelical slot9162. Theslot9162 breaks the circumferential mechanical continuity so as to reduce the torsional stiffness, but theslot9162 also breaks the circumferential shielding continuity.
• Theslot9162 may be closed using techniques discussed above. A shield patch may be wrapped around thehelical slot9162 to reach across theslot9162 and achieve circumferential shielding continuity. Or, theshield9160 may be given a larger diameter than the inner insulation layer upon which it is positioned so that upon creating theslot9162, theshield9160 may collapse to create an overlap along thehelical slot9162 to establish circumferential shielding continuity. This shield patch may be another piece of foil or may be a braided patch.
• Embodiments as disclosed in relation toFIGS. 77-80C provide for guarding a termination of a shield to reduce coupling of RF energy from the termination of the shield to filars present within an implantable medical lead for use with an implantable medical device (IMD). The guarding of the termination of the shield may be done in various ways such as by inverting the shield near the termination such that a first portion of the shield separates the termination of the shield from inner layers of the lead. Other examples may involve including separate pieces of the shield to form first and second portions, where one portion separates the termination of the other portion from the inner layers of the lead.
• FIG. 77 shows an example of an implantablemedical system10100 that includes anIMD10102 coupled to alead10108. TheIMD10102 includes ametal can10104, typically constructed of a medical grade titanium, such as grades 1-4, 5 or 9 titanium, or similar other biocompatible materials. TheIMD10102 includes aheader10106 typically constructed of materials such as polysulfone or polyurethane, that is affixed to the metal can10104. Theheader10106 is shown transparently for purposes of illustration. Theheader10106 provides a structure for securing thelead10108 to theIMD10102 and for establishing electrical connectivity between circuitry of theIMD10102 and electrodes of thelead10108.
• Thelead10108 includeselectrodes10116 on a distal end that are positioned at a stimulation site within a patient. Thelead10108 also includes connector rings10110 on a proximal end that is positioned within theheader10106. The connector rings10110 make physical contact withelectrical connections10111 within the header. Theelectrical connections10111 may include a metal contact that theconnector ring10110 rests against upon being inserted into theheader10106 where a wire extends from the metal contact into thecan10104 where the circuitry is housed. Signals applied by theIMD10102 to the connector rings10110 are conducted through thelead10108 to theelectrodes10116 to provide the stimulation therapy to the patient.
• Thelead10108 is secured in theheader10106 such as by aset screw block10112 within theheader10106 that allows at least oneset screw10114 to be tightened against at least one of the connector rings10110. Ashield10118 as shown inFIGS. 78A and 78B may be grounded to the body along one or more points down the length of the lead from theIMD10102 via capacitive coupling through the jacket or via ground rings. Theshield10118 may also be grounded at thecan10104 of theIMD10102 ofFIG. 77.
• FIGS. 78A and 78B show an example of thelead10108, where ashield10118 is present. Anouter insulation layer10120 of a lead jacket is shown transparently inFIG. 78A for purposes of illustrating theshield10118. Theshield10118 blocks at least some RF energy from directly coupling toconductive filars10124 that are present within thelead10108. Theconductive filars10124 extend the length of the lead and interconnect theproximal connectors10110 to thedistal electrodes10116 so that stimulation signals are conducted from the proximal end to the distal end of thelead10108.
• As shown inFIG. 78A, theshield10118 of this example is a braided collection of metal wires. The metal wires may be constructed of various materials such as titanium, tantalum, niobium, platinum-iridium alloy, platinum, palladium, gold, stainless steel, and their alloys, or other metals. It may be desired to utilize a biocompatible metal for theshield10118, particularly for embodiments where a portion of theshield10118 may be exposed for purposes of grounding. While theshield10118 is shown as a braid, other shield configurations may be chosen particularly where flexibility is not an issue such as a foil strip wrapped about thelead10108 in an overlapping manner.
• FIG. 78B is a cross-section that shows one example of construction of thelead10108. In this embodiment, either the guard is not provided or the guard is not present at the area where the cross-section is taken. Thus,FIG. 78B shows the general construction of thelead10108 without the specifics of the guard which are discussed below in relation toFIGS. 79A-79C and 80A-80C. Theshield10118 may be embedded within the jacket of thelead10108. One manner of constructing thelead10108 with theshield10118 is to provide aninner insulation layer10122 of the jacket that encloses thefilars10124 and anyadditional insulation layer10126, such as polytetrafluoroethylene (PTFE) that may surround each filar10124. Theshield10118 may then reside on the outer portion of theinner insulation layer10122, and theouter insulation layer10120 may then enclose theshield10118. Theouter insulation layer10120 may be added over theshield10118 and shrunk in place or may be extruded over theshield10118.
• For embodiments where it is desirable for theshield10118 to RF couple to tissue along, typically as a capacitive coupling, in addition to grounding at thecan10104 or along thelead10108, the entireouter jacket layer10120 may be relatively thin, such as on the order of 0.5 to 5 mils. Where theshield10118 grounds at one or more specific locations along its length, via a direct current coupling or a capacitive coupling, theshield10118 may be located further from the outer surface of thelead10108.
• The inner and outer insulation layers10122,10120 of the jacket may be constructed of the same or similar materials such as various flexible and biocompatible polymers, examples of which are polyurethanes and silicones. Alumen10128 may be included inside of theinner jacket10122 around which theinsulated filars10124 are coiled or otherwise positioned. Thelumen10128 may be useful, particularly for percutaneous leads10108, to allow a stylet to be inserted for purposes of pushing and steering thelead10108 into the desired position within the patient.
• FIG. 79A shows an embodiment of the implantablemedical lead10108 in an axial cross-section where termination of theshield10118 is guarded to reduce coupling of RF energy to one or more filars10124.FIG. 80A shows a radial cross-section of the same embodiment, with the cross section taken where the shield terminates. A single coiledfilar10124 is shown in this example but additional filars may be included and the filars may be of other forms such as linear cables rather than coils. In this example, theshield10118 is one continuous shield of braided metal wires, but it will be appreciated that other shields may also be used such as the wrapped foil discussed above.
• Theshield10118 of this example has aninversion10136 near the distal end of thelead10108. Thisinversion10136 creates two sections to theshield10118, afirst portion10119 that extends from theinversion10136 back to the proximal end of thelead10108 and asecond portion10121 that forms the distal termination of theshield10118. Theinversion10136 creates a guard for the shield termination.
• Thesecond portion10121 is separated from theinner insulation layer10122 as well as thefilars10124 by thefirst portion10119. Thefirst portion10119 is braided upon theinner insulation layer10122 and then may be coated with theouter insulation layer10120 with thesecond portion10121 remaining uncoated. Theinversion10136 may then be created so that thesecond portion10121 then laps onto theouter insulation layer10120 so as to be separated from contact with thefirst portion10119. Thesecond portion10121 may extend from theinversion10136 toward the proximal end by various distances, for instance ranging from about ⅛ inch to about 1 inch, such that thesecond portion10121 may be axially shorter than thefirst portion10119 which extends to the proximal end or thesecond portion10121 may also extend to the proximal end. Thesecond portion10121 may then be covered by an additionalouter insulation layer10117, made of the same or similar material as theouter insulation layer10120, if it is desired that thesecond portion10121 be physically isolated from the body tissue.
• The thickness of theouter insulation layer10120 at theinversion10136 dictates the bend radius of theinversion10136 where thesecond portion10121 laps onto theouter insulation layer10120. It may be desirable to have a bend radius that is sufficiently large, such as 0.002 inches, so that theinversion10136 does not act as a shield termination from which RF might couple to thefilars10124. The lead diameter that is allowable for a given application may dictate the relative thicknesses of each of the layers and thus set an upper limit for the bend radius of theinversion10136.
• Prior to or contemporaneously with the addition of theouter insulation layer10117, anextension10132 to theouter insulation layer10120 may be created to extend further toward the distal end where electrodes such aselectrode10130 are located. Theextension10132 may be constructed of the same or similar materials as that of the outer insulation layers10117,10120. Theelectrode10130 has afilar jumper wire10134 or the filar10124 itself that extends through thisextension10132 and between theelectrode10130 and thefilar10124. Alternatively, the area whereextension10132 is shown may be created as a continuation of theouter insulation layer10117.
• FIG. 79B shows another embodiment of the implantablemedical lead10108 in an axial cross-section where termination of theshield10118 is guarded to reduce coupling of RF energy to one or more filars10124.FIG. 80B shows a radial cross-section of the same embodiment, with the cross section taken where theshield10118 terminates. A quad coiledfilar10124 is shown in this example but additional or fewer filars may be included and the filars may be linear cables rather than coils. In this example, theshield10118 is two separate pieces forming afirst portion10123 and asecond portion10125 of theshield10118 made of braided metal wires. It will be appreciated that either or both pieces may be another form of a shield such as wrapped foil as discussed above.
• Theshield10118 of this example has thefirst portion10123 that is a separate piece that resides at the distal end of thelead10108 and may extend toward the proximal end for a relatively short distance, for instance, in the range of about ⅛ inch to about 1 inch. Thefirst portion10123 is wrapped around theinner insulation layer10122. An intervening layer ofinsulation10115 then surrounds thefirst portion10123.
• Thesecond portion10125 of theshield10118 is wrapped around the intervening layer ofinsulation10115 and is therefore physically isolated from contact with thefirst portion10123. Thesecond portion10125 then extends on to the proximal end of thelead10108 and may therefore be axially longer than thefirst portion10123. Theouter insulation layer10120 then surrounds thesecond portion10125. As a result of this configuration, thefirst portion10123 is located between the termination point at thesecond portion10125 and the inner layers including theinner insulation layer10122 andfilars10124.
• Because there is no inversion in this embodiment ofFIGS. 79B and 80B, the thickness of thelayers10115,10120 may not be as large as the thickness of theouter insulation layer10120 of the embodiment ofFIGS. 79A and 80A where that thickness established the bend radius at theinversion10136. As a result, the separation between thefirst portion10123 and thesecond portion10125 may be smaller than the separation between thefirst portion10119 and thesecond portion10121 ofFIGS. 79A and 80A. For instance, the interveninginsulation layer10115 may have a thickness ranging from about 0.002 inches to about 0.006 inches to control the separation between thefirst portion10123 andsecond portion10125.
• Theouter insulation layer10120 may be continued to extend on toward the distal end of thelead10108, including filling the area where theelectrode10130 is located. Alternatively, prior to or contemporaneously with the addition of theouter insulation layer10120, an extension layer from theouter insulation layer10120 may be created to extend further toward the distal end where electrodes such aselectrode10130 are located. The extension may be constructed of the same or similar materials as that of the outer insulation layers10117,10120.
• FIG. 79C shows another embodiment of the implantablemedical lead10108 in an axial cross-section where termination of theshield10118 is guarded to reduce coupling of RF energy to one or more filars10124.FIG. 80C shows a radial cross-section of the same embodiment, with the cross section taken where theshield10118 terminates. A quad coiledfilar10124 is shown in this example but additional filars may be included and the filars may be other forms such as linear cables rather than coils. In this example, theshield10118 is two separate pieces forming afirst portion10140 and asecond portion10142 of theshield10118 made of braided metal wires, but it will be appreciated that either piece may be another form of a shield such as wrapped foil as discussed above.
• Theshield10118 of this example has thefirst portion10140 that is a separate piece that resides at the distal end of thelead10108 and that has aninversion10138 to establish afirst sub-portion10146 and asecond sub-portion10144. Bothsub-portions10144,10146 may extend toward the proximal end of thelead10108 for a relatively short distance in the range of about ⅛ inch to about 1 inch. Thefirst sub-portion10146 is wrapped around theinner insulation layer10122. An intervening layer ofinsulation10113 then surrounds thefirst sub-portion10146.
• Thesecond portion10142 of theshield10118 is wrapped around the intervening layer ofinsulation10113 and is therefore physically isolated from contact with thefirst sub-portion10146. Thesecond portion10142 then extends on to the proximal end of thelead10108 and is therefore axially longer than thefirst sub-portion10146 and thesecond sub-portion10144. Theouter insulation layer10120 then surrounds thesecond portion10142. As a result of this configuration, thefirst sub-portion10146 is located between the termination point at thesecond portion10142 and the inner layers including theinner insulation layer10122 andfilars10124.
• Thesecond sub-portion10144 of thefirst portion10140 laps onto theouter insulation layer10120 as a result of theinversion10138. Thesecond sub-portion10144 may then be covered by an additionalouter insulation layer10127, made of the same or similar material as theouter insulation layer10120, if it is desired that thesecond sub-portion10144 be physically isolated from the body tissue.
• The thickness of both the intervening layer ofinsulation10113 and theouter insulation layer10120 at theinversion10138 dictates the bend radius of theinversion10138 where thesecond sub-portion10144 laps onto theouter insulation layer10120. It may be desirable to have a bend radius that is relatively large, such as about 0.002 inches, so that theinversion10136 does not act as a shield termination from which RF might couple to thefilars10124. The lead diameter that is allowable for a given application may dictate the relative thicknesses of each of the layers and thus set an upper limit for the bend radius similar to the upper limit for the embodiment ofFIGS. 79A and 80A.
• Theouter insulation layer10127 may be continued to extend on toward the distal end of thelead10108, including filling the area where theelectrode10130 is located. Alternatively, prior to or contemporaneously with the addition of theouter insulation layer10127, an extension layer from theouter insulation layer10120 may be created to extend further toward the distal end where electrodes such aselectrode10130 are located. The extension layer may be constructed of the same or similar materials as that of the outer insulation layers10127,10120.
• While many embodiments have been particularly shown and described, it will be understood by those skilled in the art that various other changes in the form and details may be made therein without departing from the spirit and scope of the invention.

Claims (16)

What is claimed is:

1. A method of guiding an implantable medical lead, comprising:

providing the implantable medical lead with an elongated insulative body providing a length of the lead and with a torsional stiffness over the length of the implantable medical lead, the torsional stiffness being sufficient to impart rotation over the length of the lead when rotation is applied at a point along the length that includes the torsional stiffness; and

upon insertion of a stylet with a distal guide bend into a lumen defined by the elongated insulative body of the implantable medical lead, providing a plurality of rotational couplings of the stylet to coupling features within the lumen that are defined by the elongated insulative body of the implantable medical lead such that imparting rotation directly to the implantable medical lead at the point along the length imparts rotation to the stylet to direct the distal guide bend.

2. The method ofclaim 1, wherein the coupling feature within the lumen comprises at least one of a hexagonal passage, a star passage, and a square passage.

3. The method ofclaim 1, wherein the coupling feature on the stylet comprises at least one of a hexagonal shaft, a star shaped shaft, and a square shaped shaft.

4. The method ofclaim 1, wherein providing the rotational coupling comprises providing a coupling between a proximal end of the implantable medical lead and a hub of the stylet.

5. The method ofclaim 4, wherein the coupling between the proximal end of the implantable medical lead and the hub comprises at least one of a tapered frictional fit, a threaded fit, and a splined fit.

6. The method ofclaim 1, wherein providing the implantable medical lead with the torsional stiffness over the length of the implantable medical lead comprises including a metal shield within a jacket of the implantable medical lead.

7. The method ofclaim 6, wherein the metal shield comprises a metal wire braid.

8. The method ofclaim 1, wherein the point along the length is spaced longitudinally from the rotational coupling.

9. An implantable medical lead kit, comprising:

an implantable medical lead with an elongated insulative body providing a length of the lead and with a torsional stiffness over the length of the implantable medical lead, the torsional stiffness being sufficient to impart rotation over the length of the lead when rotation is applied at any point along the length that includes the torsional stiffness; and

a stylet within a lumen defined by the elongated insulative body of the implantable medical lead, the stylet having a distal guide bend and the stylet being rotationally coupled to a plurality of coupling features within the lumen and defined by the elongated insulative body of the implantable medical lead such that imparting rotation directly to the implantable medical lead at one or more points along the length imparts rotation to the stylet to direct the distal guide bend.

10. The implantable medical lead kit ofclaim 9, wherein the coupling feature within the lumen comprises at least one of a hexagonal passage, a star passage, and a square passage.

11. The implantable medical lead kit ofclaim 9, wherein the coupling feature on the stylet comprises at least one of a hexagonal shaft, a star shaped shaft, and a square shaped shaft.

12. The implantable medical lead kit ofclaim 9, wherein a proximal end of the implantable medical lead is rotationally coupled to a hub of the stylet.

13. The implantable medical lead kit ofclaim 12, wherein the coupling between the proximal end of the implantable medical lead and the hub comprises at least one of a tapered frictional fit, a threaded fit, and a splined fit.

14. The implantable medical lead kit ofclaim 9, wherein the implantable medical lead comprises a metal shield within a jacket of the implantable medical lead that provides the torsional stiffness over the length of the implantable medical lead.

15. The implantable medical lead kit ofclaim 14, wherein the metal shield comprises a metal wire braid.

16. The implantable medical lead kit ofclaim 9, wherein the point along the length is spaced longitudinally from the rotational coupling.

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