US20040133259A1 - High impedance electrode tip - Google Patents

Abstract

An implantable lead, being either a fixed or retractable/extendable lead, having a distal tip electrode is adapted for implantation on or about the heart and for connection to a system for monitoring or stimulating cardiac activity. The electrode includes a mechanical fastener such as a fixation helix for securing the electrode to cardiac tissue, which may or may not be electrically active. The implantable electrode with a helical tip includes an electrode which has a distal end and a proximal end. A helix is disposed within the electrode, where the helix is aligned along a radial axis of the electrode. The electrode further includes one or more of the following features: the helix having a coating of an insulating material on a surface of the helix, a porous conductive surface at a base of the helix, or a porous conductive element at the end of the electrode having an insulating coating covering from 5-95% of the surface of the porous conductive element. The electrode may further include an electrode tip having a porous electrical conductive element, such as a mesh screen, disposed on a surface at the distal end of the electrode tip, which can be used as a sensing or pacing interface with the cardiac tissue.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)
• This patent application is a division of U.S. patent application Ser. No. 10/288,155, filed on Nov. 5, 2002, which is a division of U.S. patent application Ser. No. 09/121,288, filed on Jul. 22, 1998, now issued as U.S. Pat. No. 6,501,994, which is a continuation-in-part of U.S. patent application Ser. No. 08/998,174, filed on Dec. 24, 1997, entitled “RETRACTABLE LEAD WITH MESH SCREEN”, now abandoned, the specifications of which are incorporated by reference herein.[0001]
FIELD OF THE INVENTION
• The present invention relates generally to leads for conducting electrical signals to and from the heart. More particularly, it pertains to electrode tips for delivering electrical charges to the heart, and to tips which tend to reduce power consumption from cells without reducing the effective level of each pace.[0002]
BACKGROUND OF THE INVENTION
• Leads implanted in the body for electrical cardioversion or pacing of the heart are generally known in the art. In particular, electrically transmissive leads may be implanted in or about the heart to reverse (i.e., defibrillate or cardiovert) certain life threatening arrhythmias or to stimulate contraction (pacing) of the heart. Electrical energy is applied to the heart via the leads to return the heart to normal rhythm. Leads have also been used to sense conditions, materials or events (generally referred to as “sense” or “sensing”) in the body, such as in the atrium or ventricle of the heart and to deliver pacing pulses to the atrium or ventricle. Tachy leads generally can at least sense, pace, and deliver defibrillation shocks. Brady leads can at least perform the combination functions of pacing and sensing the heart. One of the available functions of the pacemaker or the automatic implantable cardioverter defibrillator (AICD) is to receive signals from a lead and interpret signals. In response to these signals, the pacemaker can decide to pace or not pace. The AICD can decide to pace or not pace, and shock or not shock. In response to a sensed bradycardia or tachycardia condition, a pulse generator produces pacing or defibrillation pulses to correct the condition. The same lead used to sense the condition is sometimes also used in the process of delivering a corrective pulse or signal from the pulse generator of the pacemaker.[0003]
• Sick sinus syndrome and symptomatic AV (atrial-ventricular) block constitute two of the major reasons for insertion of cardiac pacemakers today. Cardiac pacing may be performed by the transvenous method or by leads implanted directly onto the ventricular epicardium. Most commonly, permanent transvenous pacing is performed using a lead positioned within one or more chambers of the heart. A lead, sometimes referred to as a catheter, may be positioned in the right ventricle or in the right atrium through a subclavian vein or other vascular port, and lead terminal pins are attached to a pacemaker which is implanted subcutaneously. The lead may also be positioned in both chambers, depending on the lead, as when a lead passes through the atrium to the ventricle. Sense electrodes may be positioned within the atrium or the ventricle of the heart as appropriate for the particular condition or the choice of the medical practitioner.[0004]
• Pacemaker leads represent the electrical link between the pulse generator and the heart tissue which is to be excited. These pacemaker leads include single or multiconductor coils of insulated wire having an insulating sheath. The coils provide a cylindrical envelope or tube, many times referred to as a lumen, which provides a space into which a stiffening stylet can be inserted. The conductive coil is connected to an electrode in an electrode assembly at a distal end of a pacing lead. Typically, a terminal member is molded within a flexure sleeve at the proximal end of the pacing lead and connected to the proximal end of the conductive coil.[0005]
• After the electrode assembly is positioned at a desired location within the heart, it is desirable to provide some method for securing the electrode assembly at that location. Mechanical fixation devices are used to firmly anchor the electrodes in the heart. One type of mechanical fixation device used is a corkscrew, or a helix electrode connector. During placement of the lead, the tip of the lead travels intravenously through veins and the heart. While traveling through the veins, the helix electrode connector at the tip of the lead may snag or attach to the side wall of the vein. Since this is highly undesirable as it may cause damage or other complications to a patient, retractable helixes are one of the optional constructions which have been provided for leads. In addition, temporary caps over the helix (such as an aqueous soluble cap, particularly a water soluble, innocuous organic material such as a sugar, starch or other biologically inert, or digestible material such as sugars, starches and the like (e.g., mannitol, sorbitol)) may be formed over the helix or tip. Preferably these materials are at least soluble or dispersible and preferably are inert or even digestible.[0006]
• When using a retractable helix, the helix is extended and screwed into the heart muscle by applying a torque to the other end of the conductor without use of any further auxiliary device or with a special fixation stylet. A fixed or non-retractable helix electrode connector needs only to be positioned and secured to the heart muscle by the application of torque. If a soluble/dispersible cap is present on the helix, the cap must be given sufficient time to dissolve or disperse before complete securement of the helix electrode connector is attempted. A lead must be capable of being firmly secured into the wall of the cardiac tissue to prevent dislodgement therefrom, while avoiding perforation of the electrode completely through the cardiac tissue.[0007]
• The pulse generator circuitry and power supply work in concert with the electrodes as a system which provides electrical pulses to the heart tissue. A low impedance electrode design may increase power delivery to the heart tissue, but at the same time, this higher energy usage results in shorter battery life. Shorter battery life is undesirable, since it increases the average number of surgical procedures to perform battery replacement for a patient.[0008]
• There is a need for a body-implantable lead that has a helix for fixation to the wall of the atrium or ventricle of the heart. A separate desirable feature in body-implantable leads is for a lead having an electrode for positioning within the atrium or ventricle that allows for tissue in growth. Tissue in growth further enhances the electrical performance of the lead. The lead and electrode are further stabilized within the heart as a result of tissue in growth. Furthermore, there is a need for a relatively high pacing impedance electrode design which offers reasonable average voltage threshold with sufficient signal amplitude so that the pacing function would be effectively provided with reduced energy utilization and consequently extend battery life.[0009]
SUMMARY OF THE INVENTION
• According to the present invention, there is provided a body-implantable lead assembly comprising a lead, one end of the lead being adapted to be connected to electrical supply for providing or receiving electrical pulses. The other end of the lead comprises a distal tip which is adapted to be connected to tissue of a living body. The lead is characterized by having either a) a porous electrode at the base of the helix and/or b) an insulating coating over a portion of the helix so that the impedance is increased for the helix as compared to a helix of the same size and materials without an insulating coating. The lead also has an increased impedance or high impedance which can act to extend the life of the battery. The high or at least the increased impedance may be effected in any of a number of ways, including, but not limited to one or more of the following structures: 1) a fully insulated tissue-engaging tip with an electrode at the base of the insulated tip, 2) a partially insulated engaging tip (only a portion of the surface area of the engaging tip being insulated), 3) a mesh or screen of material at the distal end of the lead, at the base of an extended engaging tip (whether a fixed or retractable tip), 4) the selection of materials in the composition of the mesh and/or tip which provide higher impedance, 5) the partial insulative coating of a mesh or screen to increase its pacing impedance, and 6) combinations of any of these features. There may be various constructions to effect the high impedance, including the use of helical tips with smaller surface areas (e.g., somewhat shorter or thinner tips). There may also be a sheath of material inert to body materials and fluids and at least one conductor extending through the lead body. The use of these various constructions in the tip also allows for providing the discharge from the tip in a more highly resolved location or area in the tip.[0010]
• According to the present invention, there is provided a body-implantable lead assembly comprising a lead, one end being adapted to be connected to electrical supply for providing or receiving electrical pulses. The lead further comprises a distal tip which is adapted to be connected to tissue of a living body. The lead also has a high impedance to extend the life of the battery. There may be various constructions to effect the high impedance. There may also be a sheath of material at the distal end of the lead assembly, with the sheath being inert to body materials and fluids and at least one conductor extending through the lead body.[0011]
• The distal tip electrode is adapted, for example, for implantation proximate to the heart while connected with a system for monitoring or stimulating cardiac activity. The distal tip electrode includes an electrode tip (preferably with only a percentage of its entire surface area being electrically conductively exposed—only a portion of the surface is insulated—to increase its impedance), preferably a mesh screen disposed at a distal end of the electrode tip, a fixation helix disposed within the electrode tip, and a helix guiding mechanism. The mesh screen preferably is electrically active, and the area of the mesh screen and the percentage of electrically exposed surface area of the electrode tip can be changed to control electrical properties. Further, the mesh screen can entirely cover an end surface of the electrode tip, or a portion of the end surface in the form of an annular ring. In one embodiment, the helix guiding mechanism includes a hole punctured within the mesh screen. Alternatively, the helix guiding mechanism can include a guiding bar disposed transverse to a radial axis of the electrode. The helix is retractable, and is in contact with a movement mechanism. The movement mechanism provides for retracting the helix, such as during travel of the electrode tip through veins. The helix is aligned with the radial axis of the electrode and travels through the guiding mechanism. The mesh may be tightly woven or constructed so that there are effectively no openings, or the mesh can be controlled to provide controlled porosity, or controlled flow through the mesh.[0012]
• In another embodiment, the electrode tip includes a mesh screen forming a protuberance on the end surface of the electrode tip. The protuberance is axially aligned with the radial axis of the electrode. The helix travels around the protuberance as it passes through the mesh while traveling to attach to tissue within the heart. The helix also travels around the protuberance as it is retracted away from the tissue within the heart. If the mesh screen is insulated around the protuberance, then a high impedance tip is created. Advantageously, the protuberance allows for better attachment to the cardiac tissue without having the electrode tip penetrating therethrough.[0013]
• Additionally, a distal tip electrode is provided including an electrode tip, a mesh screen disposed at a distal end of the electrode tip, a fixation helix disposed within the electrode tip, and a helix guiding mechanism. The electrode tip further may include a piston for moving the helix. The piston further may include a slot for receiving a bladed or fixation stylet. When engaged and rotated, the piston provides movement to the helix. The base provides a mechanical stop for the helix and piston when retracted back into the electrode tip.[0014]
• In another embodiment, the distal tip assembly is adapted for implantation proximate to the heart while connected with a system for monitoring or stimulating cardiac activity. A fixation helix/piston assembly is housed by an electrode collar, housing, and base assembly. Attached to the proximal end of the helix is a piston which includes a proximal slot for receiving a bladed or fixation stylet. When a stylet is engaged in the slot and rotated, the piston provides movement to the helix. Depending on the embodiment, the fixation helix/piston assembly may be electrically active or inactive. The electrode collar, housing, and base all house the fixation helix/piston assembly. The proximal end of the electrode collar is attached to the distal end of the housing. Furthermore, the proximal end of the housing is attached to the distal end of the base, and the proximal end of the base is directly attached to the conductor coils of the lead.[0015]
• A mesh screen may be attached to the distal tip of the electrode collar. The mesh screen, in another embodiment, is electrically active and serves as the electrode on the distal tip assembly. The tip may then be fully insulated to increase the impedance of the tip or may be partially insulated (with preselected areas of the helix tip being insulated and other areas being non-insulated) to adjust the impedance of the tip to the specific or optimal levels desired. The area of the mesh screen can be modified to cover differing portions of the end surface of the distal tip assembly to control electrical properties of the lead. The fixation helix travels through a guiding mechanism, where the guiding mechanism allows the fixation helix to be extended and retracted. In one embodiment, the helix guiding mechanism includes a hole formed within the mesh screen. Alternatively, the helix guiding mechanism can include a guiding bar disposed transverse to a radial axis of the electrode collar. The mesh screen and/or guiding bar also serve as a full extension stop when the helix is fully extended. The base serves as a stop when the fixation helix/piston assembly is fully retracted.[0016]
• The provided electrode tip supplies a retractable helix and a mesh screen which advantageously allows for sufficient tissue in-growth. The guide mechanism provides a convenient way to direct the rotation of the helix. A further advantage of the electrode tip is the provided mechanical stop. The mechanical stop aids in preventing over-retraction of the helix during the installation or removal of the electrode tip.[0017]
• In yet another embodiment, the electrode uses a partially insulated fixation helix to provide a relatively high pacing impedance electrode. The fixation helix is insulated using insulating coatings over a portion of the fixation helix.[0018]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a first side elevational view illustrating a lead constructed in accordance with one embodiment of the present invention.[0019]
• FIG. 2A is a cross-sectional view of an electrode tip of a lead for monitoring and stimulating the heart constructed in accordance with one embodiment of the present invention.[0020]
• FIG. 2B is an end view of the electrode tip of the lead shown in FIG. 2A.[0021]
• FIG. 3A is a cross-sectional view of an electrode tip of a lead for monitoring and stimulating the heart constructed in accordance with one embodiment of the present invention.[0022]
• FIG. 3B is an end view of the electrode tip of the lead shown in FIG. 3A.[0023]
• FIG. 4A is a cross-sectional view of an electrode tip of a lead for monitoring and stimulating the heart constructed in accordance with one embodiment of the present invention[0024]
• FIG. 4B is an end view of the electrode tip of the lead shown in FIG. 4A.[0025]
• FIG. 5A is a cross-sectional view of an electrode tip of a lead for monitoring and stimulating the heart constructed in accordance with one embodiment of the present invention[0026]
• FIG. 5B is an end view of the electrode tip of the lead shown in FIG. 5A.[0027]
• FIG. 6 shows a partially insulated helical tip according to the present invention which increases the impedance of the tip as compared to a fully non-insulated helical tip.[0028]
DETAILED DESCRIPTION OF THE INVENTION
• In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which specific aspects of the broader invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice both the broad concepts of the invention as well as more limiting specific constructions, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the spirit and scope of the present invention as disclosed herein. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.[0029]
• As noted previously, there are a number of ways in which increased impedance may be effected for mechanically fastened electrode connections in atrial/ventricular implantable catheters (AVIC) systems. These include at least the following: 1) a fully insulated tissue engaging tip (at least with respect to all surfaces that are in electrical contact or electrically active physical relationship to heart muscles so that a pace would be effective if discharged at that portion of the tip), 2) a partially insulated engaging tip (only a portion of the surface area of the engaging tip being insulated, preferably there is sufficient coating so that there is at least 5%, or at least 10%, or at least 20 or 30%, or at least 40, 50 or 60%, or at least 70, 75, 80 or 90% of the surface area of the tip which can discharge to heart muscle [or as percentages of the entire tip or as percentages of the entire tip that extends physically beyond the end plane of the catheter and which may therefore penetrate tissue or muscle]), 3) a porous, electrically conductive element, such as a mesh or screen of material at the proximal end of the helix or the distal end of the lead (excluding the helix), at the base of an extended engaging tip, 4) the selection of materials in the composition of the mesh and/or tip which provide higher impedance, 5) the partial insulative coating of a porous conductive element, such as the mesh or screen to increase its impedance, and 6) combinations of any of these features. There may be various constructions to effect the increased or high impedance, including the use of helical tips with smaller surface areas (e.g., somewhat shorter or thinner tips). There may also be other elements associated with the catheter and/or leads, such as a sheath of material inert to body materials and fluids, circuitry, microcatheters, and at least one conductor extending through the lead body.[0030]
• One aspect of the present invention comprises an implantable electrode with a helical tip comprising:[0031]
• an electrode having a distal end and a proximal end; and[0032]
• a helix disposed within the electrode, which helix is aligned along a radial axis of the electrode towards the distal end, and which helix is either retractable or fixed; and[0033]
• the implantable electrode having at least one feature selected from the group consisting of:[0034]
• a) the helix having a coating of an insulating material on its surface which covers at least 5% of its surface area but less than 95% of its surface area (which is exposed beyond the distal end of the electrode),[0035]
• b) the helix extending beyond the distal end of the electrode and the distal end of the electrode having a porous conductive surface at a base of the helix,[0036]
• c) a porous conductive element such as a screen or mesh at a base of the helix, which is retractable/extendable, with the helix being either active or inactive (electrically), and[0037]
• d) a partially insulated (partially insulation coated) porous conductive element (e.g., screen or mesh) at the base of an active or inactive, retractable/extendable or fixed helix.[0038]
• The implantable electrode preferably has the helix with a coating of insulating material on its surface which covers from 5-100% (to 100% where there is an additional electrode element within the system) or 5-95% of surface area of the helix beyond the distal end of the electrode. Alternatively, the surface of the helix is that which is considered to be in electrically discharge-functional physical relationship with tissue or muscle into which it is embedded. For purposes of measuring or determining the distal end of the electrode, the tip extends beyond a tubular or cylindrical housing or structural portion which is considered the electrode, and the tip is an engaging portion that extends beyond the housing portion of the electrode. The distal end of the electrode is usually characterized as the end of the cylindrical housing or tubing carrying the tip, circuits, conductive elements, guides, etc. It is more preferred that the helix of the implantable electrode has a coating of insulating material on it surface which covers from 5-95% or 10-90% of the surface area of said helix beyond the distal end of the electrode.[0039]
• A[0040]lead10 is illustrated in FIG. 1. Thelead10 comprises alead body11, anelongate conductor13 contained within the lead body, and alead tip20 with an optionalretractable tip assembly24 contained in thelead tip20. In addition, astylet14 is shown inserted into thelead body11. A helix100 (FIGS.2A-5A), which consists of an electrical conductor coil, is contained in theretractable lead tip24. In an alternative practice of the invention, thehelix100 extends and retracts by rotation of thestylet14, as will be discussed further below. A Brady lead body is shown, although the invention could be incorporated with other leads, such as Tachy leads. Thelead body11 consists ofelectrical conductors13 which are covered by a biocompatible insulatingmaterial22. Polymers, such as silicone rubber, fluorinated resins, polyacrylates, polyamides ceramic or composite materials or other insulating material can be used for covering thelead body11.
• In one embodiment shown in FIGS. 3 and 3A, the[0041]helix100 is formed of electrically conductive material offering low electrical resistance and also resistant to corrosion by body fluids. A biocompatible metal, such as titanium or platinum-iridium alloy is an example of a suitable material. Alternatively, thehelix100 is electrically inactive or insulated. In one embodiment, thehelix100 may be coated with an insulative material (not shown) or may be constructed of a rigid, corrosion resistant, non-electrically-conductive material (e.g., a ceramic). Ahousing182, described in further detail below, is made from an electrically conductive material and covered with an insulating material such as a synthetic or natural polymer such as a silicone rubber. Thehousing182 is directly connected to an electrical conductor within thelead120. These materials are additionally suitable because they tend to be biologically inert and well tolerated by body tissue.
• The[0042]helix100 defines a lumen and thereby is adapted to receive a stiffeningstylet14 that extends through the length of the lead. Thestylet14 stiffens thelead120, and can be manipulated to introduce an appropriate curvature to the lead, facilitating the insertion of the lead into and through a vein and through an intracardiac valve to advance the distal end of thelead120 into the right ventricle of the heart (not shown). Astylet knob154 is coupled with thestylet14 for rotating thestylet14 and advancing thehelix100 into tissue of the heart.
• In one embodiment, as shown in FIGS. 2A and 2B, a[0043]lead310 has anelectrode tip320 which is provided with amesh screen330. Themesh screen330 completely encapsulates the diameter of the lead, and may serve, at least in part, as a pacing/sensing interface with cardiac tissue. If thehelix100 is electrically active, it too can help serve as a portion of a pacing or sensing interface. Themesh screen330 is of a porous construction, preferably made of electrically conductive, corrosion resistant material. Using amesh screen330 having a porous construction allows for fibrotic ingrowth. This provides for a further anchoring of thelead tip320 and also increases the sensing capability of thelead310 by increasing the surface area in contact with the cardial tissue. Themesh screen330 may be attached to anelectrode collar40, which is electrically active. In a retractable catheter system, ahousing380, which is electrically conductive, encapsulates thepiston350 and thefixation helix100.Insulation382 is disposed about thehousing380 andcollar40.
• Disposed within the[0044]lead310 is alead fastener100 for securing thelead310 to cardiac tissue. Thelead fastener100 can be disposed along theradial axis15 of theelectrode lead310. In this embodiment, the lead fastener comprises afixation helix100. Thefixation helix100 can be made electrically active or inactive as discussed above. Attached to thefixation helix100 in a retractable tip system is apiston350. Thepiston350 is configured to mate with abladed locking stylet14 at astylet slot354, and acts as an interface between thestylet14 and thehelix100. Thestylet14, coupled with thepiston350 at thestylet slot354, extends and retracts thefixation helix100 when thestylet14 is rotated. Thepiston350 can either be electrically active or inactive. Thepiston350 also has aslot352, which allows thepiston350 to mate with abase360.
• Fitted with a[0045]knob362, as shown in FIG. 2A, the base360 mates with theslot352 of thepiston350. Thebase360 serves as a stop once thefixation helix100 is fully retracted. The electricallyconductive base360 also allows passage of a bladed lockingstylet14 and attachment of electrode coils (not shown).
• In addition, the[0046]lead310 has aguide groove370. Thegroove370 is formed by puncturing a hole (not shown) within themesh screen330, although theguide groove370 can be formed by other methods known by those skilled in the art. Having a circular cross-section, theguide groove370 may have a diameter greater than that of the conductor forming thehelix100. Thegroove370 is disposed within themesh screen330, and directs thefixation helix100 from its retracted position, as illustrated in FIG. 2A, to an extended position (not shown). Thegroove370 also reversibly directs thefixation helix100 from an extended position to the retraction position.
• In a second embodiment, as shown in FIGS. 3A and 3B, a[0047]lead110 has anelectrode tip120 which is provided with amesh screen130. Themesh screen130 completely encapsulates the diameter of the lead orelectrode tip120, and serves as the pacing/sensing interface with cardiac tissue. Thescreen130 is of a porous construction, made of electrically conductive, corrosion resistant material. Using amesh screen130 having a porous construction allows for fibrotic ingrowth. This provides for a further anchoring of thelead tip120 to tissue and also increases the sensing capability of thelead110. The sensing capability is enhanced because themesh screen130 has more surface area than corresponding solid material. The ingrowth of fibrotic tissue into themesh screen130 increase the sensing capability of thelead110 by increasing the surface area in contact with the cardiac tissue. Furthermore, the geometry of themesh screen130, particularly any protuberance, as will be discussed below, creates a high pacing impedance tip.
• The[0048]mesh screen130 may form aprotuberance135 from aflat edge portion137 of themesh screen130 in a generally central portion of theelectrode tip120. Theprotuberance135 may be generally circular in cross-section, but may be any shape (e.g., truncated cylindrical, truncated pyramidal, oval, ellipsoidal, etc.) as a result of design or circumstance which provides a flat or conformable surface (preferably not a rigid, sharp face which will not conform to tissue) abutting tissue, and preferably has a diameter smaller than a diameter of thelead110. In addition, theprotuberance135 is aligned with theradial axis15 of thelead110. Sintered to anelectrode collar40, a process known by those skilled in the art, themesh screen130 is attached to theelectrode tip120. Theelectrode collar40 is electrically active.
• Disposed within the[0049]electrode lead110 is a lead fastener for securing theelectrode lead110 to cardiac tissue. The lead fastener can be disposed along theradial axis15 of theelectrode lead110. In this embodiment, the lead fastener comprises afixation helix100. Thefixation helix100 can be made electrically active or inactive to change sensing and pacing characteristics, as discussed above. Attached to thefixation helix100 is apiston150. Thepiston150 is configured to mate with abladed locking stylet14, thereby providing a movement assembly. Thestylet14 extends and retracts thefixation helix100 when thestylet14 is rotated. Thepiston150 can either be electrically active or inactive. Thepiston150 also has aslot152. Theslot152 of thepiston150 allows thepiston150 to mate with a base160 upon full retraction.
• The[0050]base160 is modified with aknob162 to mate with theslot152 of thepiston150. Theknob162 mates with thepiston150 to prevent over-retraction once thehelix100 has been fully retracted. Thestylet14 operates to advance thefixation helix100. As the implanter rotates thestylet14, thestylet14 engages thepiston150 at thestylet slot154 and rotates thepiston150, which moves thefixation helix100 through aguide groove170. Theguide groove170 is for ensuring that thefixation helix100 is properly guided out of and into the end of the electrode. Once thefixation helix100 is fully retracted, thebase160 serves as a mechanical stop. The base160 also allows passage of a bladed lockingstylet14 and attachment of electrode coils. Additionally, thebase60 is electrically active.
• The[0051]electrode lead110 also has aguide groove170. Thegroove170 is formed by puncturing a hole within the mesh screen. Having a circular cross-section, thegroove170 has a diameter greater than that of the conductor forming thehelix100. Thegroove170 is disposed within themesh screen130, and directs thefixation helix100 from its retracted position, as illustrated in FIG. 2A, to an extended position (not shown). During implantation, after the electrode is in contact with tissue at the desired location in the heart, thestylet14 is rotated which causes the piston to advance the fixation helix out of thegroove170. As thefixation helix100 is placed in an extended position, thehelix100 travels throughgroove170 and circles around theprotuberance135. Thegroove170 also directs thefixation helix100 from an extended position to the retracted position. Advantageously, themesh screen130 prevents the implanter from overextension and advancing thehelix100 too far into the tissue. An electricallyconductive housing180 encapsulates both thepiston50 and thefixation helix100.Insulation182 covers thehousing180, thecollar40, and a portion of themesh screen130. Theinsulation182 over themesh screen130 controls the impedance of theelectrode tip120.
• In a third embodiment as shown in FIGS. 4A and 4B, a[0052]lead10 has anelectrode tip20 which is provided with amesh screen30. Themesh screen30 completely encapsulates the diameter of the lead tip. Sintered to anelectrode collar40, themesh screen30 is attached to theelectrode tip20. Theelectrode collar40 is electrically active. Ahousing80 is disposed about thehelix100, and is electrically active.Insulation82, encompasses thehousing80 andcollar40.
• Disposed within the[0053]lead10 is a lead fastener for securing thelead10 to cardiac tissue. The lead fastener can be disposed along theradial axis15 of thelead10. In this embodiment, the lead fastener comprises afixation helix100. Thefixation helix100 can be made electrically active or inactive to change sensing and pacing characteristics.
• The[0054]helix100 is of a well known construction. Using a conductor coil such ashelix100 has been shown to be capable of withstanding constant, rapidly repeated flexing over a period of time which can be measured in years. Thehelix100 is wound relatively tightly, with a slight space between adjacent turns. This closely coiled construction provides a maximum number of conductor turns per unit length, thereby providing optimum strain distribution. The spirally coiled spring construction ofhelix100 also permits a substantial degree of elongation, within the elastic limits of the material, as well as distribution along the conductor of flexing stresses which otherwise might be concentrated at a particular point.
• Attached to the[0055]fixation helix100 is apiston50. Thepiston50 is configured to mate with abladed locking stylet14. Thepiston50 advances thefixation helix100 once the lead is placed in position within the heart. Thepiston50 can either be electrically active or inactive. Thepiston50 also has aslot52 and astylet slot54. Thestylet14 couples with thestylet slot54 and extends or retracts thefixation helix100 when thestylet14 is rotated. Theslot52 of thepiston50 allows thepiston50 to mate with a base60 when thehelix100 is retracted to prevent over retraction. Thebase60 is configured with aknob62 to mate with theslot52 of thepiston50. Once thefixation helix100 is fully retracted, thebase60 serves as a stop at full retraction. The base60 also allows passage of a bladed lockingstylet14 and attachment of electrode coils. In addition, thebase60 is electrically active.
• The[0056]lead10 also includes a guidingbar70. Extending across the diameter of the tip, the guidingbar70 is generally cylindrical in shape. The guidingbar70 directs thefixation helix100 from its retracted position, as illustrated in FIG. 2A, to an extended position (not shown) as thepiston52 advances thehelix100. The guidingbar70 also directs thefixation helix100 as it is retracted from an extended position to the retraction position through the mesh screen. Although a guidingbar70 is described, other types of guiding mechanisms can be used such as helical passageways, threaded housings, springs, and are considered within the scope of the invention. Additionally, thelead10 is provided with a seal (not shown) for preventing entry of body fluids and tissue from entering the lead through the opening therein. The seal could be a puncture seal between thepiston50 and thebase60. Alternatively, O-rings could be used to seal the electrode.
• In a fourth embodiment as shown in FIGS. 5A and 5B, a[0057]lead210 has anelectrode tip220 which is provided with amesh screen230. Themesh screen230 forms an annular ring having an open center, where the annular ring is centered at aradial axis15 of theelectrode lead210. Themesh screen230 provides more surface area than a smooth tipped electrode which aids in sensing. The removal of the center portion of the mesh screen creates a high impedance pacing tip due to the nature of the surface geometry. Sintered, fused, bonded, adhesively secured or mechanically attached to anelectrode collar40, themesh screen230 is attached to theelectrode tip220. Theelectrode collar40 is electrically active.
• Disposed within the[0058]lead210 is a lead fastener for securing thelead210 to cardiac tissue. The lead fastener can be disposed along theradial axis15 of theelectrode lead210. In this embodiment, the lead fastener comprises afixation helix100. Thefixation helix100 can be made electrically active or inactive as discussed above. Attached to thefixation helix100 is apiston250. Thepiston250 has astylet slot254 and is configured to mate with abladed locking stylet14. Thestylet14, coupled with thepiston250 at thestylet slot254, extends and retracts thefixation helix100 when thestylet14 is rotated. Thepiston250 can either be electrically active or inactive. Thebase260 serves as a stop once thefixation helix100 is fully retracted. The base260 also allows passage of a bladed lockingstylet14 and attachment of electrode coils. Thebase60 is electrically active.
• Additionally, the electrode lead also has a guiding[0059]bar270. The guidingbar270 directs thefixation helix100 from its retracted position, as illustrated in FIGS.5A and5B, to an extended position (not shown). The guidingbar270 also directs thefixation helix100 from an extended position to the retracted position. Although a guidingbar270 has been described, other types of mechanisms could be used to extend the helix, and are considered within the scope of the invention. Ahousing280 encapsulates thepiston250 and thefixation helix100, andinsulation282 is disposed over thehousing280 andcollar40.
• Insulation generally covers the housing, the collar, and a portion of the electrical discharge surface (e.g., the cathode, the helix and/or the porous material or mesh). The insulation over the mesh screen further controls the impedance of the electrode tip. The insulated coating, whether present on the helix or the mesh or other elements which are potentially electrically active or on which electrical activity is to be suppressed, should be biocompatible, non-thrombogenic, and otherwise safe for implantation. The insulation coating should be of dimensions which effect the insulation, increase the impedance (where desired), but which dimensions do not interfere with the performance of the tip, the lead or the helix or the health of the patient. The insulation is present as a coating ( a material which tends to conform to the surface rather than completely reconfigure it, as would a lump of material). The coating usually should be at least 0.5 microns in thickness, usually between 0.5 and 100 microns, preferably between 1.0 and 30 or 50 microns, more preferably between 1 and 20 microns, still more preferably between 1.5 and 15 microns, and most preferably between 1.5 or 2.0 microns and 10 or 15 microns. The coating may be provided by any convenient process, such as electrophoretic deposition, dip coating, spin coating, in situ polymerization, vapor deposition, sputtering and the like. Any insulating material is useful, such as polymers, ceramics, glasses, and the like, but because of their convenience in application, flexibility and availability, polymers are preferred. Polymers from such classes as polyesters, polyamides, polyurethanes, polyethers, polysiloxanes, polyfluorinated resins, polyolefins, polyvinyl polymers, polyacrylates (including polymethacrylates), and the like may be used with various leads and tips according to the practice of the present invention. PARYLENE is a preferred material, as described herein, with a thickness of between 1.5 and 10 microns.[0060]
• In yet another embodiment, a partially insulated fixation helix is used to provide a relatively high impedance electrode design. Leads comprising a distal or electrode end and a proximal or connector end may be used. A “miniature” wire-in-basket porous electrode may be sintered upon the distal end of a metallic pin, provided with a blind hole. Circumferential to this subassembly, a sharpened wire fixation helix may be positioned and attached at a general location proximal to the electrode by any convenient means which allows electrical continuity. This attachment includes, but is not limited to, crimping, spot welding, laser welding, the use of grooves upon the surface of the pin, the use of thin metallic overband (also not shown) or any combination thereof. A portion of this fixation helix is provided with an extremely thin layer of a biostable, biocompatible polymer, which, inter alia, provides electrical insulation between the fixation helix and the cardiac tissue. In one embodiment, the insulated portion is the majority of the fixation helix, leaving a relatively small uninsulated region of fixation helix. This approach offers increased impedance to reduce energy dissipation in pulsing functions, such as pacing functions. Other varying embodiments include, but are not limited to, a portion which is approximately or substantially equal to half of the fixation helix, and a portion which is approximately or substantially equal to a minority of the fixation helix. Such embodiments provide different amounts of uninsulated region and different amounts of impedance. The thin coating of electrically insulating coating must usually be at least 1 micron in thickness to provide a significant insulating effect, depending upon its insulating ability and properties. The thickness of the coating is limited primarily by physical limitations on the system. The coating can not be so thick as to interfere with the fastening ability of the helix or to increase the size of the helix beyond that which is tolerable for the use of the helix and the patient. Typically, the coating is at least one micron up to about 100 microns, more typically the coating is between 1 and 30 microns, preferably between 1.5 and 20 microns, more preferably between 1.5 and 15 microns, and most preferably between 2 and 10 microns. The material used for the coating should, of course, be biocompatible and even more preferably non-thrombogenic. Materials such as PARYLENE™, polyurethanes, polyacrylates (including polymethacrylates), polyesters, polyamides, polyethers, polysiloxanes, polyepoxide resins and the like can be used. PARYLENE material includes a thermoplastic film polymer base upon para-xylylene. Crosslinked polymers within these classes may be preferred for their resistance to breakdown and their physical durability. As the coating is to be maintained within the body of a recipient, the coating composition should not be water-soluble or aqueous soluble within the parameters and environment encountered within animal bodies (e.g., it should not be soluble within blood, serum or other body fluids with which it might come into contact).[0061]
• To the proximal end of this pin, a metallic conductor coil may be conveniently attached to provide electrical connection to the implantable pacemaker (not shown) by means of a connector. In one embodiment, local (e.g., steroid or other medicinal) therapy is provided by a (e.g., circumferential) steroid/polymer matrix positioned immediately proximal to the porous electrode. In one embodiment, the circumferential steroid/polymer matrix is provided with a distal taper. Other embodiments include other distal configurations, including, but not limited to, non-tapered or “inflated” configurations. In one embodiment, an internalized, medicinal or biologically active (e.g., steroid) releasing matrix is used. Proximal to this biologically active (e.g., steroid) eluting matrix, a generally cylindrical polymeric tubing (this is the preferred shape, but the shape is a matter of choice)[0062]820 is used to provide electrical insulation of this entire assembly. In one embodiment, the lead is “unipolar.” In one embodiment, an ablative protective covering positioned over the entirety of distal end is used (not shown). One example of such a covering is the mannitol “Sweet Tip”® electrode of Guidant Corporation's Cardiac Rhythm Management Group. In one embodiment, a “bipolar” lead is provided with the distal electrode features described.
• During an in vitro evaluation of this electrode design, polymeric coatings intended to partially insulate the fixation helix were prepared and evaluated. In one embodiment, the PARYLENE coating is extremely thin (˜3μ), providing a coating with uniform coverage which is adherent to the metallic substrate, and which is controllable to provide an abrupt margin. The silicone rubber coating is known to be somewhat thicker (˜10μ), uniform in coverage, somewhat less adherent to the metallic substrate, and controllable to an abrupt margin. Other coatings may be used without departing from the spirit and scope of the present invention.[0063]
• The PARYLENE or other insulative coating effectively increases in vitro “pacing impedance.” Application of a non-continuous or partially extensive coating of an electrically insulating polymer such as PARYLENE to the metallic fixation helix produces the desired increase in impedance compared to an uninsulated helix as well as other existing designs. For example, it has been demonstrated that one embodiment using a coated fixation helix provides a pacing impedance of over approximately 800 ohms which is larger than the impedance of some electrodes using an uncoated fixation helix. The post-implant pacing impedance of an embodiment using a coated fixation helix remains higher than that of typical electrodes using an uncoated fixation helix. In one experiment, a coated fixation helix using PARYLENE as an insulating layer provided over 1200 ohms average pacing impedance on the day of implantation and over 900 ohms ten days after the implant.[0064]
• Additionally, post-implant average voltage threshold of the PARYLENE insulated miniaturized electrode is less than the other high impedance electrodes. Such performance is considered to be desirable. In one experiment, an embodiment with a[0065]coated fixation helix802 having a voltage threshold of approximately 0.2 volts on the day of implant was measured at about 0.7 volts at ten days after the implant (using a 0.5 ms pulse width). An electrode with an uncoated fixation helix demonstrated over 0.8 volts average voltage threshold at ten days after the implant, illustrating the benefits of the coated fixation helix.
• An additional benefit is that the coated fixation helix embodiments may provide an improvement in both the implant as well as post-implant average S-wave amplitude detection.[0066]
• The miniaturized high impedance, positive fixation porous electrode technology described here provides the following advantages over the prior art. For one example, the coated fixation helix embodiments provide an electrode where the benefits of high impedance pacing are realized through downsizing the porous electrode and insulating the fixation helix. Downsizing of the porous electrode may be accomplished, for example, by having a smaller porous (e.g., mesh) electrode supported on a non-conductive surrounding support element (e.g., a polymeric or composite film with a mesh central area, particularly a mesh truncated conical or pyramidal area of flexible, conductive mesh). An area of the completely conductive mesh may also be discontinuously coated leaving a conductive central or conductive raised area, particularly surrounding a contact, engaging element, or helix. Further, an external steroid collar provides a fabrication advantage since such a component can be readily mass produced compared to smaller components with elaborate profiles. Still further, fabrication of a lead with this external collar is streamlined. The higher impedance design conserves battery power to provide longer battery life with fewer battery replacements. Other benefits exist which are not described in detail herein, however, which those skilled in the art will appreciate.[0067]
• FIG. 6 shows a high[0068]impedance catheter tip800 with a partially insulatedtip802 and a partially insulatedmesh808. The partially insulated tip (or helix)802 extends from a base,proximal end830 to a distal, pointed end834 with amiddle portion836 lying betweenproximal end830 and distal end834.Helix802 comprises one fullyinsulated section804 which begins at distal, pointed end834 and extends to, and ends with,middle portion836 and oneuninsulated section806 which extends from the end of the fully insulated section withinmiddle portion836 to base,proximal end830. The partially insulatedmesh808 comprises afirst area810 of themesh808 which is insulated and second are812 of themesh808 which is not insulated. The impedance of the catheter tip can be readily controlled by the amount of surface area of the helical tip itself and the area of the mesh (if present) which is insulated. With a fixed conductivity in the tip and the mesh (if present), the impedance can be increased by increasing the percentage of the surface area of the tip or mesh which is insulated.
• A[0069]hole820 is shown in themesh808. Themesh808 may be flat and flush with theend822 of thecatheter816 or may be partially wrapped (not shown) over theend820 or inside theend820 to affix the mesh to thecatheter816. Themesh808 may also be hemispherical, truncated conical, truncated pyramidal or any other shape which may assist in allowing themesh808 to more compliantly contact tissue (not shown) surface to transmit the pacing signal or discharge. Within thecatheter816 may be a soluble, elutable or dispersible material which carries medication or biologically active material along with the catheter. For example, anti-inflammatants, antibiotics, analgesics, pain-reducing medication, vitamins, anti-viral medication, or the like may be transmitted to the attachment site along with the catheter by inclusion within amaterial814 carried within or on thecatheter816.
• The coating of insulation on the helical tip or mesh may be applied by any convenient method, including, but not limited to coating (e.g., dip coating), printing, spraying, brush application, resist application and removal and the like. The insulation may also contain active ingredients (such as those recited within material[0070]814) to benefit the patient. The insulation carrying the active material must not be soluble, so a polymer or other material that is porous or has elutable materials must be used. The material delivery does not have to be coextensive with the life of the implant or the tip, and delivery of the material may be desirable only over a short time period after insertion of the helical tip and catheter.
• A soluble or dispersible protective cap may also be placed over the helical tip to reduce the possibility of any incidental damage while catheterizing or moving the tip within a patient. As previously noted, the cap material should preferably be biocompatible or even digestible and may include such materials as natural and synthetic materials such as sugars, starches, gelation (unhardened), gums, resins, polymers, and the like. All components of the catheter and tip which are exposed to the tissue or fluids within a patient should be non-thrombogenic, and bio-acceptable. There are extensive classes of commercially available materials which meet these needs for metal, polymeric, composite and other materials described within the practice of the present invention.[0071]
• It is to be understood that the above description is intended to be illustrative, and not restrictive. Although the use of the lead has been described for use in a cardiac pacing system, the lead could as well be applied to other types of body stimulating systems. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.[0072]

Claims (7)

What is claimed:

1. A distal tip electrode adapted for implantation on or about the heart and for connection to a system for monitoring or stimulating cardiac activity, said electrode comprising:

an electrode tip;

a mesh screen disposed at a distal end of the electrode tip;

a surface at the distal end of the electrode tip;

a fixation device disposed within said electrode, said fixation device adapted for travel along radial axis of the electrode through said surface;

a guiding mechanism for directing movement of the fixation device during travel; and

a movement assembly, said movement assembly for providing movement to said fixation device.

2. The distal tip electrode as recited inclaim 1, wherein said fixation device comprises a helix.

3. The distal tip electrode as recited inclaim 1, wherein said movement assembly comprises a piston.

4. The distal tip electrode as recited inclaim 3, wherein the piston has a slot therein, and the base further comprises a knob, said slot for mating with said knob.

5. The distal tip electrode as recited inclaim 3, wherein the slot is mated with said knob to form a stop mechanism for said fixation device.

6. The distal tip electrode as recited inclaim 1, wherein the mesh screen has a groove guide disposed therein.

7. The distal tip electrode as recited inclaim 3, wherein said distal tip electrode further comprises a seal, said seal disposed between said piston and said base.

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