US20140330287A1 - Devices and techniques for anchoring an implantable medical device - Google Patents

Abstract

Anchoring mechanisms for an implantable electrical medical lead that is positioned within a substernal space are disclosed. The anchoring mechanisms fixedly-position a distal portion of the lead, that is implanted in the substernal space.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit of priority from U.S. Provisional Application No. 61/820,024, filed on May 6, 2013, the content of which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
• The present application relates to implantable medical devices. In particular, methods, techniques devices are disclosed for anchoring implantable medical leads.
BACKGROUND OF THE INVENTION
• Electrical stimulation of body tissue and organs is often used as a method of treating various conditions. Such stimulation is generally delivered by means of electrical contact between a pulse generator device and a target site via one or more implantable medical electrical leads connected to the pulse generator device; implantable leads typically include one or more stimulation electrodes joined to a distal portion of the lead, which are positioned and anchored in proximity to the target site.
• In patients at high risk of ventricular fibrillation, the use of an implantable cardioverter defibrillator (ICD) system has been shown to be beneficial. An ICD system includes an ICD, which is a small battery powered electrical shock device, may include an electrical housing, or can electrode, that is coupled to one or more implantable medical leads that are implanted within the heart. If an arrhythmia is sensed, the ICD may send a pulse via the implantable leads to shock the heart and restore its normal rhythm. Owing to the inherent surgical risks in attaching and replacing implantable leads directly within or on the heart, methods have been devised to achieve a similar effect to that of a transvenous ICD system that is connected directly to the heart without placing implantable leads within the heart or attaching the leads directly to the heart.
• Subcutaneous implantable cardioverter-defibrillator (SubQ ICD) systems have been devised to deliver electrical impulses to the heart by the use of one or more implantable leads that are placed subcutaneously on the torso. In order to effectively electrically stimulate the heart, the distal end of the implantable lead may be oriented longitudinally spanning from approximately the xiphoid to the high sternal area.
• Various implantable medical lead structures and methods for positioning and anchoring lead electrodes in proximity to target sites have been developed over the years. New structures and methods are necessary to anchor lead electrodes for emerging therapy delivery requirements.
SUMMARY
• Aspects in accordance with principles of the present invention relate to an implantable medical electrical lead for applying electrical stimulation to bodily tissue. The implantable lead is adapted to be introduced through an access point adjacent to the sternum and a distal portion is navigated into the substernal space. With this in mind, the implantable lead includes a lead body and an anchoring assembly. The lead body has a proximal section adapted to be electronically coupled to a power source and a distal section forming at least one exposed electrode surface.
• In accordance with embodiments of the disclosure, the anchoring assembly may be located along a length of the lead body that is configured to be located within the substernal space, such as at or near the distal lead end. In other embodiments, the anchoring assembly may be located along a length of the lead body that is configured to be located at or near the access point into the substernal space.
• Other aspects of the disclosure relate to a method of anchoring an implantable lead system. The method comprises subcutaneously advancing the lead to an access point into a substernal space of a patient, navigating a distal end of the lead to an implantation site within the substernal space, placing the distal end of the lead within the substernal space, orienting a fixation element in a pre-determined direction relative to the substernal space, and fixedly-securing a segment of the lead at the access point with a fixation element that secures the lead at an intersection between the subcutaneous space and the substernal space.
BRIEF DESCRIPTION OF THE DRAWINGS
• The following drawings are illustrative of particular embodiments of the invention and therefore do not limit the scope of the invention, but are presented to assist in providing a proper understanding. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. The present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements, and:
• FIG. 1A is a front view of a patient implanted with implantable cardiac system;
• FIG. 1B is a side view the patient implanted with implantablecardiac system10;
• FIG. 1C is a transverse view of the patient implanted with implantable cardiac system;
• FIG. 2 depicts an embodiment of a lead anchoring mechanism of a lead of the implantable cardiac system;
• FIG. 3 depicts an embodiment of a lead anchoring mechanism of a lead of the implantable cardiac system;
• FIG. 4 depicts an embodiment of a lead anchoring mechanism of a lead of the implantable cardiac system;
• FIG. 5 depicts an embodiment of a lead anchoring mechanism of a lead of the implantable cardiac system;
• FIG. 6 depicts an embodiment of a lead anchoring mechanism of a lead of the implantable cardiac system; and
• FIG. 7 is a flow diagram illustrating an exemplary method of implanting a lead according to an embodiment.
DETAILED DESCRIPTION
• The disclosure describes techniques, components, assemblies, and methods for anchoring a lead in a patient's substernal space or extra-pericardium, with the lead being attachable to a subcutaneously implanted medical device. A distal end of the lead is positioned at a target implant site and anchored therein.
• In this disclosure, “substernal space” refers to the region defined by the undersurface between the sternum and the body cavity, but not including the pericardium. In other words, the region is posterior to the sternum and anterior to the ascending aorta. The substernal space may alternatively be referred to by the terms “retrosternal space” or “mediastinum” or “infrasternal” as is known to those skilled in the art and includes the region referred to as the anterior mediastinum. The substernal space may also include the anatomical region described in Baudoin, Y. P., et al., entitled “The superior epigastric artery does not pass through Larrey's space (trigonum sternocostale).”Surg.Radiol.Anat.25.3-4 (2003): 259-62 as Larrey's space. For ease of description, the term substernal space will be used in this disclosure, it being understood that the term is interchangeable with any of the other aforementioned terms.
• In this disclosure, the term “extra-pericardial” space refers to region around the outer heart surface, but not within the pericardial sac/space. The region defined as the extra-pericardial space includes the gap, tissue, bone, or other anatomical features around the perimeter of, and adjacent to the pericardium.
• In this specification, “anchor” means to fix a position of an object relative to tissue to minimize movement of the object relative to the tissue. Thus, although there may be small movements of the object relative to the tissue, arising for example from body movements of the patient that give rise to small deflections of the object within the tissue, the object is nevertheless “anchored” in the tissue. It is to be understood that features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise.
• FIGS. 1A-C are conceptual diagrams of apatient12 implanted with an example implantablecardiac system10.FIG. 1A is a front view ofpatient12 implanted with implantablecardiac system10.FIG. 1B is aside view patient12 with implantablecardiac system10.FIG. 1C is a transverse view ofpatient12 with implantablecardiac system10.
• Implantablecardiac system10 includes an implantable cardiac defibrillator (ICD)14 connected to afirst lead16 and asecond lead18. Thefirst lead16 and thesecond lead18 may be utilized to provide an electrical stimulation therapy such as pacing or defibrillation. For example, lead16 may provide defibrillation therapy whilelead18 may provide pacing therapy, or vice versa, while in other embodiments, both lead16 and lead18 may provide pacing therapy or defibrillation therapy. In the example illustrated inFIGS. 1A-C ICD14 is implanted subcutaneously on the left midaxillary ofpatient12.ICD14 may, however, be implanted at other subcutaneous locations onpatient12 as described later.
• Lead16 includes a proximal end that is connected toICD14 and a distal end that includes one or more electrodes.Lead16 extends subcutaneously fromICD14 towardxiphoid process20. At a location nearxiphoid process20, lead16 bends or turns and extends subcutaneously superior, substantially parallel tosternum22. The distal end oflead16 may be positioned near the second or third rib. However, the distal end oflead16 may be positioned further superior or inferior depending on the location ofICD14 and other factors. Although illustrated as being offset laterally from and extending substantially parallel tosternum22 in the example ofFIGS. 1A-C, lead16 may be implanted oversternum22, offset fromsternum22, but not parallel to sternum22 (e.g., angled lateral fromsternum22 at either the proximal or distal end).
• Lead16 includes adefibrillation electrode24, which may include an elongated coil electrode or a ribbon electrode, toward the distal end oflead16.Lead16 is placed such that a therapy vector betweendefibrillation electrode24 and a housing or can electrode ofICD14 is substantially across the ventricle ofheart26.
• Lead16 may also include one or more sensing electrodes, such assensing electrodes28 and30, located toward the distal end oflead16. In the example illustrated inFIGS. 1A-C, sensingelectrode28 and30 are separated from one another bydefibrillation electrode24.ICD14 may sense electrical activity ofheart26 via a combination of sensing vectors that include combinations ofelectrodes28 and30 and the housing or can electrode ofICD14. For example,ICD14 may obtain electrical signals sensed using a sensing vector betweenelectrodes28 and30, obtain electrical signals sensed using a sensing vector betweenelectrode28 and the conductive housing or can electrode ofICD14, obtain electrical signals sensed using a sensing vector betweenelectrode30 and the conductive housing or can electrode ofICD14, or a combination thereof. In some instances,ICD14 may even sense cardiac electrical signals using a sensing vector that includesdefibrillation electrode24.
• Lead18 includes a proximal end that is connected toICD14 and a distal end that includes one or more electrodes.Lead18 extends subcutaneously fromICD14 towardxiphoid process20. At a location nearxiphoid process20lead18 bends or turns and extends superior upward in the substernal space. In one example, lead18 may be placed in themediastinum36 and, more particularly, in the anterior mediastinum. The anterior mediastinum is bounded laterally bypleurae40, posteriorly bypericardium38, and anteriorly bysternum22.Lead18 may be implanted within the mediastinum such that one ormore electrodes32 and34 are located over a cardiac silhouette of the ventricle as observed via fluoroscopy. In the example illustrated inFIGS. 1A-C, lead18 is located substantially centered understernum22. In other instances, however, lead18 may be implanted such that it is offset laterally from the center ofsternum22. Although described herein as being implanted in the substernal space, the mediastinum, or the anterior mediastinum, lead18 may be implanted in other extra-pericardial locations.
• Lead18 includeselectrodes32 and34 located near a distal end oflead18.Electrodes32 and34 may comprise ring electrodes, hemispherical electrodes, coil electrodes, helical electrodes, ribbon electrodes, or other types of electrodes, or combination thereof.Electrodes32 and34 may be the same type of electrodes or different types of electrodes. In the example illustrated inFIGS. 1A-C electrode32 is a hemispherical electrode andelectrode34 is a ring or coil electrode.
• ICD14 may deliver pacing pulses toheart26 via a pacing or therapy vector that includes any combination of one or both ofelectrodes32 and34 and a housing electrode or can electrode ofICD14. For example,ICD14 may deliver pacing pulses using a pacing or therapy vector betweenelectrodes32 and34, deliver pacing pulses using a pacing or therapy vector betweenelectrodes32 and the conductive housing or can electrode ofICD14, deliver pacing pulses using a pacing or therapy vector betweenelectrodes34 and the conductive housing or can electrode ofICD14, or a combination thereof. In some instances,ICD14 may deliver pacing therapy via a therapy vector between one of electrode32 (or electrode34) anddefibrillation electrode24. In still further instances,ICD14 may deliver pacing therapy via a therapy vector between one of electrode32 (or electrode34) and one ofsensing electrodes28 or30.ICD14 may generate and deliver the pacing pulses to provide anti-tachycardia pacing (ATP), bradycardia pacing, post shock pacing, or other pacing therapies or combination of pacing therapies. In this manner, ATP therapy or post shock pacing (or other pacing therapy) may be provided in an ICD system without entering the vasculature or the pericardial space, nor making intimate contact with the heart.
• ICD14 may generate and deliver pacing pulses with any of a number of amplitudes and pulse widths to captureheart26. The pacing thresholds ofheart26 when delivering pacing pulses substernally usinglead18 may depend upon a number of factors, including location ofelectrodes32 and34, location ofICD14, physical abnormalities of heart26 (e.g., pericardial adhesions), or other factors. The pacing thresholds needed to captureheart26 tend to increase with shorter pulse widths. In the case of ATP,ICD14 may deliver pacing pulses having longer pulse widths than conventional ATP pulses to reduce the amplitude of the pacing pulses. For example,ICD14 may be configured to deliver pacing pulses having pulse widths or durations of greater than or equal to one (1) millisecond. In another example,ICD14 may be configured to deliver pacing pulses having pulse widths or durations of greater than or equal to ten (10) milliseconds. In a further example,ICD14 may be configured to deliver pacing pulses having pulse widths or durations of greater than or equal to fifteen (15) milliseconds. In yet another example,ICD14 may be configured to deliver pacing pulses having pulse widths or durations of greater than or equal to twenty (20) milliseconds. Depending on the pulse widths,ICD14 may be configured to deliver pacing pulses having pulse amplitudes less than or equal to twenty (20) volts, deliver pacing pulses having pulse amplitudes less than or equal to ten (10) volts, deliver pacing pulses having pulse amplitudes less than or equal to five (5) volts, deliver pacing pulses having pulse amplitudes less than or equal to two and one-half (2.5) volts, deliver pacing pulses having pulse amplitudes less than or equal to one (1) volt. Typically the lower amplitudes require longer pacing widths as illustrated in the experimental results. Reducing the amplitude of pacing pulses delivered byICD14 reduces the likelihood of extracardiac stimulation.
• ICD14 may sense electrical activity ofheart26 via a combination of sensing vectors that include combinations ofelectrodes32 and34 and the housing or can electrode ofICD14. For example,ICD14 may obtain electrical signals sensed using a sensing vector betweenelectrodes32 and34, obtain electrical signals sensed using a sensing vector betweenelectrode32 and the conductive housing or can electrode ofICD14, obtain electrical signals sensed using a sensing vector betweenelectrode34 and the conductive housing or can electrode ofICD14, or a combination thereof. In some instances,ICD14 may sense electrical activity ofheart26 via a sensing vector between one of electrode32 (or electrode34) andelectrodes24,28 and30 oflead16.ICD14 may deliver the pacing therapy as a function of the electrical signals sensed via the one or more of the sensing vectors oflead18. Alternatively or additionally,ICD14 may deliver the pacing therapy as a function of the electrical signals sensed via one or more of the sensing vectors oflead16.
• ICD14 also analyzes the sensed electrical signals from one or more of the sensing vectors oflead18 and/or one or more of the sensing vectors oflead16 to detect tachycardia, such as ventricular tachycardia or ventricular fibrillation. In some instances,ICD14 delivers one or more ATP therapies via the one or more pacing or therapy vectors oflead18 in response to detecting the tachycardia in an attempt to terminate the tachycardia without delivering a defibrillation shock. If the one or more ATP therapies are not successful or it is determined that ATP therapy is not desired,ICD14 may deliver one or more defibrillation shocks viadefibrillation electrode24 oflead16.
• The configuration described above inFIGS. 1A-1C is directed to providing ventricular pacing vialead18. In situations in which atrial pacing is desired in addition to or instead of ventricular pacing, lead18 may be positioned further superior. A pacing lead configured to deliver pacing pulses to both the atrium and ventricle may have more electrodes. For example, the pacing lead may have one or more electrodes located over a cardiac silhouette of the atrium as observed via fluoroscopy and one or more electrodes located over a cardiac silhouette of the ventricle as observed via fluoroscopy. A pacing lead configured to deliver pacing pulses to only the atrium may, for example, have one or more electrodes located over a cardiac silhouette of the atrium as observed via fluoroscopy. In some instances, two substernal pacing leads may be utilized with one being an atrial pacing lead implanted such that the electrodes are located over a cardiac silhouette of the atrium as observed via fluoroscopy and the other being a ventricle pacing lead being implanted such that the electrodes are located over a cardiac silhouette of the ventricle as observed via fluoroscopy.
• ICD14 may include a housing that forms a hermetic seal that protects components ofICD14. The housing ofICD14 may be formed of a conductive material, such as titanium.ICD14 may also include a connector assembly (also referred to as a connector block or header) that includes electrical feedthroughs through which electrical connections are made between conductors within leads16 and18 and electronic components included within the housing. As will be described in further detail herein, housing may house one or more processors, memories, transmitters, receivers, sensors, sensing circuitry, therapy circuitry and other appropriate components.Housing34 is configured to be implanted in a patient, such aspatient12.
• Leads16 and18 include a lead body that includes one or more electrodes located near the distal lead end or elsewhere along the length of the lead body. The lead bodies ofleads16 and18 also contain one or more elongated electrical conductors (not illustrated) that extend through the lead body from the connector assembly ofICD14 provided at a proximal lead end to one or more electrodes ofleads16 and18. The lead bodies ofleads16 and18 may be formed from a non-conductive material, including silicone, polyurethane, fluoropolymers, mixtures thereof, and other appropriate materials, and shaped to form one or more lumens within which the one or more conductors extend. However, the techniques are not limited to such constructions.
• The one or more elongated electrical conductors contained within the lead bodies ofleads16 and18 may engage with respective ones ofelectrodes24,28,30,32, and34. In one example, each ofelectrodes24,28,30,32, and34 is electrically coupled to a respective conductor within its associated lead body. The respective conductors may electrically couple to circuitry, such as a therapy module or a sensing module, ofICD14 via connections in connector assembly, including associated feedthroughs. The electrical conductors transmit therapy from a therapy module withinICD14 to one or more ofelectrodes24,28,30,32, and34 and transmit sensed electrical signals from one or more ofelectrodes24,28,30,32, and34 to the sensing module withinICD14.
• Thelead18 further includes one or more anchoring mechanisms that are positioned along the length of the lead body. The anchoring mechanisms affix thelead18 that is implanted in a substernal space in a fixed location to prevent dislodging of thelead18 once it is implanted. For example, thelead18 may be anchored at one or more locations situated between the distal lead end positioned within the substernal space ofpatient12 and a point along the length of the portion of the lead body at or near the insertion point of the lead body into the substernal space. The one or more anchoring mechanism(s) may either engage cartilage, bone, fascia, muscle or other tissue ofpatient12 or may simply be wedged therein to affix the lead under the sternum to prevent excessive motion or dislodgment. Furthermore, it should be understood that various anchoring mechanisms described in this disclosure may additionally be utilized for delivery of a stimulation therapy as is known in the art.
• In accordance with various embodiments, this disclosure describes anchoring mechanisms that are integrated into the lead body. In such embodiments, a portion or segment of the lead body may be formed with materials that function to encase conductors and other elements internal to the lead while also anchoring the lead within the implant environment.
• In alternative embodiments, anchoring mechanisms of the disclosure are described as discrete elements that may be formed in line with the lead body. In some embodiments, the discrete components may be provided in a fixedly-secured relationship to the lead body. In other embodiments, the anchoring mechanism may be detachedly coupled in a sliding relationship over the lead body.
• The anchoring mechanisms may include a passive anchoring mechanism, an active anchoring mechanism or a combination of both. In one embodiment, the anchoring mechanism is coupled along a length of the lead body and it may also function as an electrically active element. Examples of passive anchoring mechanisms include flanges, disks, pliant tines, flaps, porous structures such as a mesh-like element that facilitates tissue growth for engagement, bio-adhesive surfaces (such as those described in U.S. Pat. No.: 8,594,809, which is incorporated herein by reference in its entirety), and/or any other non-piercing elements. Examples of active anchoring mechanisms may include rigid tines, prongs, burbs, clips, screws, and/or other projecting elements that pierce and penetrate into tissue to anchor the lead. As another example of an active anchoring mechanism, the lead may be provided with a side helix for engaging tissue. It is contemplated that any of these anchoring mechanisms will be formed from materials including shape memory alloys such as Nitinol to facilitate the deployment of the lead.
• The various examples of the anchoring mechanisms may be deployable. As such, the anchoring mechanism assumes a first state during maneuvering of the lead (during which time the lead is disposed within a lumen of a delivery system or over a guidewire or stylet) to the desired implant location. Subsequently, the anchoring mechanism assumes a second state following the release of the lead from the delivery system into the substernal space to thereby anchor the distal end portion of the lead body relative to the adjacent tissue.
• In addition or alternatively, the lead may be anchored through a suture that fixedly-secures the lead to the cartilage, musculature, tissue or bone at the access point into the substernal space ofpatient12. In some embodiments, the suture may be sewn to the patient12 through pre-formed suture holes to thepatient12.
• As shown inFIG. 1A, ananchoring mechanism50aoranchoring mechanism50b(collectively “anchoring mechanism50”) may be provided along the lead body to couple thelead18 at an access point through which the distal end of thelead18 is inserted into the substernal space. The access point is any location that provides access into the substernal space. In one exemplary embodiment, the access point is adjacent to or below the xiphoid process (also referred to as “subxiphoid”). The access point may also be at the notch (not shown) that connects the xiphoid process to the sternum. In other embodiments, the substernal space may also be accessed through the manubrium.
• An example of theanchoring mechanism50aincludes a suture or clip or other fastener that anchors the lead body to thepatient12. Theanchoring mechanism50aembodied as a fastener may be coupled directly to the lead body or to a suture sleeve such as that described in U.S. Pat. No. 5,273,053, issued to Pohndorf and incorporated herein by reference in its entirety. Theanchoring mechanism50ais fixedly-coupled to cartilage, musculature, tissue or bone at the entry point into the substernal space at or near the access point at which site the body of the lead18 transitions from the subcutaneous tissue into the substernal space ofpatient12.
• In an embodiment, theanchoring mechanism50athat is positioned at the access point may further be formed to accommodate the curvature of the patient12 anatomy. In other words, the body of theanchoring mechanism50aembodied, for example as a suture sleeve, may be malleable or pre-shaped to conform to the bend angle of the site at which thelead18 transitions from the subcutaneous tissue into the substernal space ofpatient12. As such, the suture sleeve may include a segment having a preformed bend angle of approximately 90 degrees. Thus, the anchoring sleeve may be positioned partially in the subcutaneous tissue and partially within the substernal space. The anchoring sleeve may be coupled to the patient12 at one or more points along the length of the anchoring sleeve.
• Theanchoring mechanism50amay further be constructed to facilitate tissue in-growth for long-term fixation of thelead18. To promote such tissue in-growth, theanchoring mechanism50amay be formed having a multi-layer construction or having pores. In some embodiments, theanchoring mechanism50amay be constructed having a cross-linked structure. In accordance with other embodiments, the materials for construction of theanchoring mechanism50ahaving a multi-layer structure may include bio-absorbable materials which will degrade a short time after implant. Theanchoring mechanism50amay also include a collagen layer which has been pre-treated to promote the tissue growth.
• An example of theanchoring mechanism50bmay include a fixation element that is disposed continuously or partially around the body oflead18 to couple the lead18 to the access point. The anchoring mechanism may be fixedly coupled to the lead or slidingly-disposed over the lead, such as the anchoring member described in U.S. Pat. No. 5,476,493 to Muff, which is configured to be movable axially along the length of the lead body, to facilitate positioning of theanchoring mechanism50bat a point suitable for affixation to tissue adjacent to the xiphoid process. In other words, anchoringmechanism50bmay be disposed around the lead body in a sliding relationship to facilitate navigation and placement of the distal end of the lead into the substernal space and the subsequent movement of theanchoring mechanism50bto the site for fixation.
• In some embodiments, lead18 further includes a reinforceddistal end36 that is formed to facilitate anchoring of thelead18 within the substernal space. The reinforceddistal end36 of thelead18 prevents flexing of thelead18 responsive to body motions. Thedistal end36 may be formed from a material having a greater stiffness coefficient relative to that of the material of the lead body, or with a coating, or a resilient member—such as a coil—coupled over the lead body, any of which is fabricated to impart stiffness to thedistal end36. The reinforceddistal end36 exhibits characteristics that eliminate or minimize the motion of the distal end of the lead. As such, thedistal end36 functions to anchor thelead18 within the tissue ofpatient12.
• In addition, the reinforceddistal end36 may be constructed to facilitate tissue in-growth for long-term fixation of thelead18. To promote such tissue in-growth, thedistal end36 may be formed having a multi-layer construction or having pores. In some embodiments, thedistal end36 may be constructed having a cross-linked structure. In accordance with other embodiments, the materials for construction of thedistal end36 having a multi-layer structure may include bio-absorbable materials which will degrade a short time after implant. Thedistal end36 may also include a collagen layer which has been pre-treated to promote the tissue growth.
• A backfilling process may be utilized to increase the stiffness coefficient of the reinforceddistal end36 relative other segments of the body oflead18. For example, thelead18 body may be formed with multiple insulative layers with the backfill material—such as a medical adhesive or additional material—being added to reinforce thedistal end36. In other embodiments, the reinforceddistal end36 may be formed with materials having an increased rigidity, relative to the rest of the lead body. For example, the reinforceddistal end36 may be fabricated from such materials as an ultra-high molecular density polyethylene, polyester or other high tensile strength fiber or plastic. In other examples, a lead body oflead18 that is manufactured of relatively soft plastics of low tensile strength may be reinforced to provide a reinforceddistal end36 by increasing the layers of material used in the region ofdistal end36.
• The examples illustrated inFIGS. 1A-C are exemplary in nature and should not be considered limiting of the techniques described in this disclosure. In other examples,ICD14, lead16, and lead18 may be implanted at other locations. For example,ICD14 may be implanted in a subcutaneous pocket in the right chest. In this example, lead16 may be extend subcutaneously from the device toward the manubrium of the sternum and bend or turn and extend subcutaneously inferiorly from the manubrium of the sternum, substantially parallel with the sternum and lead18 may extend subcutaneously from the device toward the manubrium of the sternum to the desired location and bend or turn and extend substernally inferiorly from the manubrium of the sternum to the desired location.
• In the example illustrated inFIG. 1,system10 is an ICD system that provides pacing therapy. However, these techniques may be applicable to other cardiac systems, including cardiac resynchronization therapy defibrillator (CRT-D) systems, cardioverter systems, or combinations thereof.
• In addition, it should be noted thatsystem10 may not be limited to treatment of a human patient. In alternative examples,system10 may be implemented in non-human patients, e.g., primates, canines, equines, pigs, bovines, ovines, and felines. These other animals may undergo clinical or research therapies that may benefit from the subject matter of this disclosure.
• FIG. 2 depicts alead anchoring mechanism60 that includes a plurality ofstruts62 that are disposed over thelead18 in a sliding relationship and are configured to expand from a collapsed configuration to an expanded configuration such that the plurality ofstruts62 expand to press against tissue surrounding the implant location.
• In one embodiment, thestruts62 may be displaced distally—relative to a mid-axis of thelead18—by employing a deployment member (not shown) that causes both distal-ward movement and expansive displacement of thestruts62 into the expanded state. Other deployment mechanisms may include pneumatic activation (fluid or gas activated), or direct connection via rods, or any other type of proximally applied torque that causes force transfer to deploy thestruts62.
• According to one exemplary embodiment, thelead anchoring mechanism60 is made from a super-elastic material. Thestruts62 may be formed from a tubular collar with material being removed to form two or more expandable struts62.
• Thelead18 inFIG. 2 further includes a canteddistal portion64. As illustrated, the body oflead18 is pre-shaped to be canted at an angle in the range of 10 degrees to 90 degrees, relative to the remaining, proximal, portion of the lead body. The pre-shape canteddistal portion64 may be constructed by providing an inner layer having a shape memory material over this section of the lead body. During delivery of the lead body, thelead18 may be positioned with a catheter or other delivery system that causes the canteddistal portion64 to be straightened. Therefore, the bias of thedistal portion64 is such that the introduction of a straight stylet into a center lumen of the lead body or the insertion of lead body into a guide catheter may cause the bend to be straightened. Upon insertion into the substernal space, the canteddistal portion64 permits the lead body to assume the pre-determined shape thereby causing thedistal portion64 to anchor to tissue within the substernal space.
• Although the canteddistal portion64 is shown in conjunction with theanchoring mechanism60, it should be noted that alternative embodiments of thelead18 may simply include the canteddistal portion64 without theanchoring mechanism60.
• InFIG. 3, ananchoring mechanism70 is coupled to the distal end of thelead18. Theanchoring mechanism70 may be configured as a flange or pad mounted to the distal end of thelead18. Theanchoring mechanism70 includes amajor surface72 that is greater than a minor surface (not shown) that is perpendicular to the major surface. Themajor surface72 is characterized by a width that is greater relative to the width of the minor surface. When coupled to thelead18, the major surface is oriented in line with an imaginary axis of the body oflead18 running continuously between the proximal end and the distal end. The cross-sectional profile of theanchoring mechanism70 is dimensioned to be greater than a cross-sectional profile of thelead18. For example, theanchoring mechanism70 may be configured having a width that is greater than that of thelead18 as viewed from a side perspective or side cross-section.
• Electrode32 may be attached to thelead18 overlying a portion oflead anchoring mechanism70. In this mounting configuration, theelectrode32 may be oriented to direct the field of the stimulation energy in a pre-determined direction at the implant location.
• In one embodiment, anchoringmechanism70 may include a mesh-like structure having pores that permit ingrowth of tissue that affixes to the anchoring mechanism. In other embodiments, theanchoring mechanism70 may include a bioreactive adhesion layer (not shown) such as that described in the U.S. Patent Application No. 2009/0270962, with the bioreactive adhesion layer being coupled to the surface of theanchoring mechanism70. In such an embodiment, a cover (not shown) may be utilized to seal off the bioreactive adhesion layer from the external environment until the anchoring mechanism is situated at an appropriate implant site.
• FIG. 4 illustrates ananchoring mechanism80 having a combinationpassive fixation element82 and anactive fixation element84 coupled to the distal end oflead18. The illustration depicts thefixation element82 andfixation element84 in an expanded or deployed configuration. Thepassive fixation element82 may be a disk that expands radially relative to the width of the lead body to define a circumference that is larger than the circumference of the lead body. Theanchoring mechanism80 further illustratesactive fixation element84 that may be a helix that extends in axially from the distal end of the lead body and is configured for insertion into tissue. Thefixation element84 may be screwed out of the distal tip of the lead body, for example, through a rotational force that is imparted by rotating the lead body.
• FIG. 5 illustrates ananchoring mechanism90 coupled along a length of the lead body. Theanchoring mechanism90 comprises a side helix that engages with tissue. The side helix may be formed as a coil wound over the lead body. Engagement of the tissue occurs through protrusion of the side helix in a direction that is perpendicular to an imaginary axis from the proximal to the distal end of the lead.
• FIG. 6 is a side view ofanchoring mechanism100 positioned at a proximal end ofelectrode32 of a lead of a medical device according to an embodiment. Theanchoring mechanism100 is positioned proximal from theelectrode32 on the lead body oflead18 and includes proximal tines that are formed of flexible or pliant material such as polymeric materials for example, as silicone rubber or polyurethane to passively fixate to tissue. In another embodiment, the tines may be formed of a rigid material such as titanium or PEEK for active fixation to the tissue. During deployment of theanchoring mechanism100, the tines are folded such that the tine elements are retracted or constrained against the lead body. This may be accomplished by positioning thelead18 within a lumen of a delivery system having a diameter smaller than the width defined by the expanded tines. Upon delivery to the proper location, thelead18 is released from the delivery system allowing the tines to return to their extended position whereby they push against or pierce the tissue improving both acute and chronic fixation.
• FIG. 7 is a flow diagram illustrating an exemplary method of implanting a lead according to an embodiment of the disclosure. In particular, the method involves implantation of a medical lead in a substernal space underneath the sternum and fixedly-securing the distal end of the lead to patient tissue.Lead18
• (FIGS. 1-6) comprises one example of such a medical lead that may be implanted in the substernal space.
• Thelead18 is implanted in a region that is underneath the sternum and within the mediastinum space. The mediastinum space may include the region that is posterior to the sternum and anterior to the pericardial sac from the xiphoid to the manubrium and bounded laterally on the left and right by the internal thoracic arteries. A lead implanted in the substernal space may provide a stimulation therapy, such as a pacing therapy (including anti-tachy pacing, post-shock pacing, chronic pacing) or a defibrillation therapy or both.
• A delivery system such as that disclosed in U.S. Patent Application No.: 61/820,014, “Systems And Methods For Implanting A Medical Electrical Lead Within A Substernal Space” which is hereby incorporated by reference in its entirety, may be utilized to implant the lead. When used, the delivery system is navigated into the substernal space through an access point on the patient (202). The navigation of the delivery system to the appropriate location may be aided by various navigation aids discussed in the 61/820,014 application, including: a radiopaque marker that is visualized through fluoroscopy, signals obtained from the distal end of the delivery system body, and a directional indicator on the delivery system. Again, the access point may be any location on the tissue of the patient12 where an incision is made to provide access into the substernal space.
• Attask204, a distal end of the lead is navigated to the implantation site within the substernal space. The lead body may extend from a stimulation therapy generating device, such asdevice14, that is positioned subcutaneously, such as at the left mid-axillary of the patient, and tunneled toward the xiphoid process. The navigation of the lead from the xiphoid process into the substernal space may be performed such that the distal end of the lead is directed toward the jugular notch from the xiphoid process in a generally axial direction.
• The distal end of the lead is positioned within the substernal space at a location over a cardiac silhouette of the ventricle as observed via fluoroscopy. In particular, the electrodes may be oriented towards a target stimulation site (206). In one example, the desired orientation of the electrode may be achieved by orienting an anchoring mechanism that is coupled to the lead in a direction that causes the electrode to be positioned in a direction towards the target stimulation site. For example, the electrode may be formed integrally with an anchoring mechanism such as that described inFIG. 3. In this configuration, the movement, including rotational or longitudinal movement, of the anchoring mechanism triggers movement of the electrode in the corresponding direction which facilitates orientation of the electrode in the desired direction.
• Attask208, the lead is anchored to tissue surrounding the implant environment. The lead may be anchored at the distal end, proximate to the distal end or any other location along the length of the lead between the access point into the xiphoid process and the distal end of the lead. In doing so, the portion of the lead within the substernal space is anchored to prevent dislodgment of the lead.
• In some embodiments, the anchoring mechanism may be configured in a first retracted configuration during the navigation of the lead and re-configured into a second expanded configuration when the lead is released within the substernal space. In other embodiments, the anchoring mechanism is retracted from an interior portion of the lead. Additionally, the lead body may be sutured at or near the xiphoid process to fixedly couple the lead.
• Attask210, the delivery system is retracted from the patient after the lead has been guided to the implant site.
• As described herein, anchoring devices, systems and methods in accordance with various embodiments are provided that facilitate implantation and stabilization of a lead in the substernal space. In alternative implementations, the devices, systems and methods may be utilized for lead implantation and fixation in locations other than the substernal space including but not limited to the aforementioned extra-pericardial space.
• Various examples have been described. It is contemplated that the features described in the different embodiments may be combined to create additional embodiments. All such disclosed and other examples are within the scope of the following claims.

Claims (30)

What is claimed is:

1. An implantable medical system comprising:

a stimulation therapy generator;

a first elongate lead coupled to the stimulation therapy generator having a proximal end and a distal end;

an electrode coupled to the distal end of the first elongate lead; and

an anchoring mechanism disposed along a length of the first elongate lead configured to fixedly-secure the first elongate lead within a substernal space underneath the sternum.

2. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises a reinforcement member coupled to the distal end of the lead that is configured to prevent movement of the lead responsive to a dislodgment force from the tissue at the implant location.

3. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises a canted distal portion formed at the distal end of the lead such that the canted distal portion engages tissue within the substernal space to anchor the lead.

4. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises a distal section of the lead that is configured having a material that includes a greater stiffness coefficient relative to the proximal section of the lead.

5. The implantable medical system ofclaim 1, wherein the anchoring mechanism is configured to position the electrode in a pre-determined orientation relative to a target stimulation therapy site that is not within the substernal space.

6. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises a flange having at least one major surface that is oriented in a parallel configuration with a length of the lead.

7. The implantable medical system ofclaim 1, wherein the anchoring mechanism is configured to fixedly-secure the first elongate lead at an access point into the substernal space, wherein a distal end of the lead is configured to be tunneled through a pathway across subcutaneous tissue for insertion into the substernal space.

8. The implantable medical system ofclaim 1, wherein the anchoring mechanism includes a porous structure disposed at the distal end of the lead.

9. The implantable medical system ofclaim 8, wherein the anchoring mechanism comprises an in-growth member having a substance configured to promote tissue growth for anchoring the implantable stimulation lead to tissue.

10. The implantable medical system ofclaim 1, wherein the anchoring mechanism is slidingly-disposed along a length of a body of the first elongate lead, and wherein the anchoring mechanism is moveable along the length of the body during navigation of the lead.

11. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises a passive fixator disposed along a length of a body of the first elongate lead and configured to engage tissue.

12. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises an active fixator disposed along a length of a body of the first elongate lead and configured to engage tissue.

13. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises an expandable coil.

14. The implantable medical system ofclaim 1, wherein the anchoring mechanism comprises an expandable porous structure having pores for tissue engagement.

15. The implantable medical system ofclaim 1, wherein the first elongate lead and the anchoring mechanism are configured for deployment into the substernal space through a delivery system such that the anchoring mechanism remains in the first constrained configuration during delivery of the lead to the substernal space and is released to the second expanded configuration subsequent to release of the lead into the substernal space.

16. The implantable medical system ofclaim 1, further comprising a second elongate lead coupled to the stimulation therapy generator and wherein the second elongate is configured for implantation at a subcutaneous implant location.

17. A method of implanting a medical system, comprising:

subcutaneously advancing a first lead through a subcutaneous space from a subcutaneously positioned implantable medical device to an access point into a substernal space;

navigating a distal end of the first lead to an implantation site within the substernal space;

placing the distal end of the first lead within the substernal space;

orienting a fixation element in a pre-determined direction relative to the substernal space; and

fixedly-securing a segment of the first lead at the access point with a fixation element that secures the lead at an intersection between the subcutaneous space and the substernal space.

18. The method of implanting the medical system ofclaim 17, wherein the orientation of the fixation element is configured to conform to curvature of a transition from the subcutaneous tissue into the substernal space.

19. The method of implanting the medical system ofclaim 17, further comprising performing an incision at a xiphoid process of a patient to create the access point into substernal space.

20. The method of implanting the medical system ofclaim 17, further comprising anchoring the distal end of the first lead to the tissue.

21. The method of implanting the medical system ofclaim 20, wherein the anchoring comprises suturing the distal end to the tissue.

22. The method of implanting the medical system ofclaim 20, wherein the anchoring comprises deploying a fixation element for coupling with the tissue.

23. The method of implanting the medical system ofclaim 22, wherein the fixation element is selected from the group consisting of a prong, burb, clip, screw, flange, disk, flap, and a porous structure.

24. The method of implanting the medical system ofclaim 20, wherein the anchoring comprises deploying an anchoring mechanism oriented in a first retracted configuration into the substernal space such that the deployed anchoring mechanism is oriented in a second expanded configuration when positioned in the substernal space.

25. The method of implanting the medical system ofclaim 20, wherein the orientation of the anchoring mechanism triggers a corresponding orientation of an electrode of the first lead towards a target stimulation therapy site.

26. The method of implanting the medical system ofclaim 20, wherein the anchoring mechanism is configured in a first retracted configuration during the navigation of the lead and configured into a second expanded configuration when the lead is placed within the substernal space.

27. The method of implanting the medical system ofclaim 17, wherein navigating the first lead comprises:

inserting the first lead into a delivery system having a distal end portion that is positioned within the substernal space, wherein the distal end of the delivery system comprises a sheath having a lumen into which the first lead is disposed;

advancing the distal end of the first lead towards the distal end portion of the delivery system; and

retracting the delivery system over the first lead from the substernal space.

28. The method of implanting the medical system ofclaim 17, further comprising positioning an electrode disposed on the distal end of the first lead such that a field of an electrical stimulation applied through the electrode is directed toward a stimulation site.

29. The method of implanting the medical system ofclaim 17, further comprising subcutaneously advancing a second lead for fixation in subcutaneous tissue, wherein the first lead delivers a pacing stimulation therapy and the second lead delivers a defibrillation stimulation therapy.

30. The method of implanting the medical system ofclaim 17, wherein the first lead delivers a combination therapy including pacing stimulation and defibrillation stimulation.

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