WO2004091717A2

WO2004091717A2 - Subcutaneous cardiac lead with fixation

Info

Publication number: WO2004091717A2
Application number: PCT/US2004/010916
Authority: WO
Inventors: Adam W. Cates; Ron Heil; Curtis Charles Lindstrom; Jason Alan Shiroff; Pete Kelley; Darrell Orvin Wagner
Original assignee: Cardiac Pacemakers, Inc.
Priority date: 2003-04-11
Filing date: 2004-04-09
Publication date: 2004-10-28
Also published as: EP1617894A2; WO2004091717A3; JP2006522661A

Abstract

Implantable subcutaneous devices and methods employ a lead and/or electrode for cardiac monitoring and/or stimulation. One or more fixation elements are included, for example, expandable elements, porosity, helical fixation elements, grooves, ridges, tines, tines with barbs, spring-loaded tines, flexible or collapsible tines, and other fixation mechanisms configured to actively and/or passively secure one or both of the electrode or body of the lead in subcutaneous non-intrathoracic tissue acutely, chronically, or acutely and chronically. A method of implanting subcutaneous leads according to the present invention involves providing a lead comprising a lead body, an electrode, and one or more fixation elements, and securing one or both of the lead body and the electrode to subcutaneous non-intrathoracic tissue at one or more fixation sites using the fixation elements. The method may involve use of a delivery device, such as a sheath, for lead delivery to a subcutaneous non-intrathoracic implant site.

Description

SUBCUTANEOUS CARDIAC LEAD WITH FIXATION

FIELD OF THE INVENTION

The present invention relates generally to leads for subcutaneously implantable cardiac monitoring and/or stimulation devices, and, more particularly, to fixation elements for subcutaneous leads and/or electrodes.

BACKGROUND OF THE INVENTION

Implantable cardiac rhythm management systems have been used as an effective treatment for patients with serious arrhythmias. These systems typically include one or more leads and circuitry to sense signals from one or more interior and/or exterior surfaces of the heart. Such systems also include circuitry for generating electrical pulses that are applied to cardiac tissue at one or more interior and/or exterior surfaces of the heart. For example, leads extending into the patient's heart are connected to electrodes that contact the myocardium for monitoring the heart's electrical signals and for delivering pulses to the heart in accordance with various therapies for treating arrhythmias.

Typical implantable cardioverter/defibrillators (ICDs) include one or more endocardial leads to which at least one defibrillation electrode is connected. Such ICDs are capable of delivering high-energy shocks to the heart, interrupting the ventricular tachyarrythmia or ventricular fibrillation, and allowing the heart to resume normal sinus rhythm. ICDs may also include pacing functionality.

Although ICDs are very effective at preventing Sudden Cardiac Death (SCD), most people at risk of SCD are not provided with implantable defibrillators. Primary reasons for this unfortunate reality include the limited number of physicians qualified to perform transvenous lead/electrode implantation, a limited number of surgical facilities adequately equipped to accommodate such cardiac procedures, and a limited number of the at-risk patient population that may safely undergo the required endocardial or epicardial lead/electrode implant procedure. For these reasons, subcutaneous ICDs are being developed.

Current ICDs utilize subcutaneous electrodes that may be prone to migrate in the subcutaneous tissue layer due to, for example, gravity, patient mobility, or patient interaction (e.g., twiddler's syndrome). Such migration may be detrimental to the performance of a subcutaneous electrode system because monitoring, detection, and defibrillation efficacy is typically very sensitive to electrode position/orientation.

Existing subcutaneous leads have typically relied on redundancy to address the problem of subcutaneous electrode migration. For example, a subcutaneous array may include three long coil electrodes, even though all three coils are not necessary when properly placed. Because migration may occur, the three long fingers provide adequate " coverage to maintain defibrillation efficacy.

There is a need for more precise electrode placement that solves the problem of subcutaneous electrode migration. There is a further need for a fixation approach for subcutaneous leads that provides for improved subcutaneous system performance, such as by providing more consistent defibrillation and or pacing thresholds and potentially lowering such thresholds. The present invention fulfills these and other needs, and addresses deficiencies in known systems and techniques.

SUMMARY OF THE INVENTION Implantable subcutaneous devices and methods employ a lead and/or electrode for cardiac monitoring andor stimulation. The devices and methods employ one or more . fixation elements including, for example, expandable elements, porosity, helical fixation elements, grooves, ridges, tines, tines with barbs, spring-loaded tines, flexible or collapsible tines, and other fixation mechanisms configured to actively and/or passively secure one or both of the electrode or body of the lead in subcutaneous non-intrathoracic tissue acutely, chronically, or acutely and chronically.

One embodiment of an implantable subcutaneous lead is directed to a lead body with an electrode supported by the lead body, the electrode configured for subcutaneous non-intrathoracic placement within a patient. One or more fixation elements are provided on the implantable lead, the fixation elements configured to passively secure one or both of the electrode and the lead body in subcutaneous non-intrathoracic tissue.

The fixation elements may include tines, tines with barbs, collapsible tines, rigid tines, spring-loaded tines, and tines formed from a polymer,, a metal, or a shape memory alloy. The tines may be situated on the lead to permit axial displacement of the. lead in a distal direction, and to be set in subcutaneous non-intrathoracic tissue in response to axial displacement of the lead in a proximal direction. An implantable subcutaneous lead system is also contemplated, which includes a lead having a lead body and an electrode, the lead configured for subcutaneous non- intrathoracic placement within a patient. A plurality of fixation elements are provided on the lead that passively secure one or both of the electrode and the lead body in subcutaneous non-intrathoracic tissue. A delivery sheath is configured to introduce the lead to a desired subcutaneous non-intrathoracic location within the patient. The lumen of the sheath is dimensioned to at least partially collapse tines of the fixation elements while permitting axial displacement of the lead within the lumen.

Another embodiment of a lead in accordance with the present invention is directed to an implantable lead system that includes a lead body having a body cross-sectional diameter. A subcutaneous electrode is supported by the lead body, the subcutaneous electrode configured for subcutaneous non-intrathoracic placement within a patient. A fixation element is provided on the implantable lead, the fixation element configured to secure the lead in subcutaneous non-intrathoracic tissue. The fixation element may be, for example, a helical coil that fixes the lead in tissue.

The fixation element may also incorporate an electrode for monitoring and or stimulation. The lead may have a fixation element with a cross-sectional diameter larger than the lead , body's cross-sectional diameter. In another embodiment, the lead has a lead longitudinal axis and the fixation element has a fixation element longitudinal axis, and the lead longitudinal axis is non-coincident with respect to the fixation element longitudinal axis. . An implantable lead in accordance with another embodiment of the present ' ^• invention is directed to a lead body with a supported electrode. The electrode is configured for subcutaneous non-intrathoracic placement within a patient. An expanding fixation element is provided on the implantable lead and configured to secure one or both of the subcutaneous electrode and the lead body in subcutaneous non-intrathoracic tissue. Useful expandable fixation elements include, for example, sponges, such as scleral sponges, and expandable portions such as an expandable polymer containing an additive. A delivery apparatus comprising a sheath may be included that is configured to introduce the lead to a desired subcutaneous non-intrathoracic location within the patient. The sheath may be used to compress the expandable fixation element.

Methods in accordance with the present invention involve providing a lead having a lead body, a cardiac electrode, and a plurality of fixation elements. The lead body, the cardiac electrode, and/or one or more of the plurality of fixation elements are manipulated to provide fixation. The plurality of fixation elements are configured to be securable in subcutaneous non-intrathoracic tissue, and may include tines that are configured to fixedly engage subcutaneous non-intrathoracic tissue. A position or an orientation of the plurality of fixation elements may facilitate axial displacement of the lead in a distal direction and resist axial displacement of the lead in a proximal direction. A position or an orientation of the plurality of fixation elements may alternately or additionally facilitate axial displacement of the lead in a distal direction and resist rotational displacement of the lead in both clockwise and counterclockwise directions. A removable sheath having a lumen may be provided to modify a position or an orientation of at least some of the plurality of fixation elements when the lead is within the lumen. Removing the lead from the sheath, may enable a plurality of fixation elements for passive engagement, and may return at least some of the plurality of fixation elements to an initial position or orientation when they are advanced beyond, or retracted from, the lumen of the sheath.

Other embodiments of the plurality of fixation elements are configured to permit longitudinal advancement of the lead in a distal direction and to resist longitudinal advancement of the lead in a proximal direction. The fixation elements may include at least one acute fixation element configured to acutely securing one or both of the lead body and the cardiac electrode, and at least one chronic fixation element configured to chronically securing one or both of the lead body and the cardiac electrode.

Another embodiment of a method in accordance with the present invention involves providing a lead having a lead body, a cardiac electrode, and an expandable fixation element configured to expandably secure the lead in subcutaneous non-intrathoracic tissue. The expandable fixation element may be. expanded at a fixation site. The expandable fixation element may expand to an effective diameter larger than the diameter of the lead body. The method may further involve providing a sheath having a lumen, advancing the lead through the sheath, and removing the sheath from the lead.

Removing the sheath may involve longitudinally splitting the sheath, enabling at least one fixation element of the one or more expandable fixation elements. Advancing the ' lead through the sheath may involve modifying a position or an orientation of at least one expandable fixation element of the one or more expandable fixation elements, such as by compressing at least one expandable fixation element of the one or more expandable fixation^' elements.

An example of an acute fixation element is a helical coil configured to acutely secure the one or both of the lead body and the cardiac electrode to the subcutaneous non- intrathoracic tissue. Another example of an acute fixation element is a suture configured to acutely secure the one or both of the lead body and the cardiac electrode to the subcutaneous non-intrathoracic tissue. An example of a chronic fixation element is a portion of the lead configured to promote tissue ingrowth between the one or both of the lead body and the cardiac electrode and the subcutaneous non-intrathoracic tissue. One embodiment of an implantable subcutaneous lead is directed to a lead body with an electrode supported by the lead body, the electrode configured for subcutaneous non-intrathoracic placement within a patient. The lead includes acute fixation elements such as a helical coil or suture loop in combination with one or more chronic fixation elements provided on the implantable lead, the fixation elements configured to secure one or both of the electrode and the lead body in subcutaneous non-intrathoracic tissue.

An implantable subcutaneous lead system in accordance with the present invention is directed^'to a lead having a lead body and an electrode, the lead configured for subcutaneous non-intrathoracic placement within a patient. A chronic fixation element is provided on the lead that secures one or both of the electrode and the lead body in subcutaneous non-intrathoracic tissue. A delivery sheath is configured to introduce the lead to a desired subcutaneous non-intrathoracic location within the patient.

The above summary of the present invention is not intended to describe each embodiment or every implementation of the present invention. Advantages and attainments, together with a more complete understanding of the invention, will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

. Figures 1A and IB are views of a transthoracic cardiac monitoring and/or stimulation device as implanted in a patient; Figure 2 illustrates a lead in accordance with the present invention, inserted in a dissected subcutaneous path leading from the can; Figure 3 A is a plan view of a lead enclosed within a sheath prior to deployment of fixation elements in accordance with the present invention;

Figures 3B and 3C are plan views of a lead having an expanding region before (Figure 3B) and after (Figure 3C) expansion in accordance with the present invention; Figure 4 is a magnified view of one embodiment of a lead having an electrode, the lead implemented to include fixation arrangements in accordance with the present invention;

Figure 5 is a magnified view of another embodiment of a lead having an electrode, the lead implemented to include fixation arrangements in accordance with the present invention;

Figure 6 is a magnified view of a further embodiment of a lead having an electrode, the lead implemented to include fixation arrangements in accordance with the present invention;

Figure 7 is a magnified view of yet another embodiment of a lead having an electrode,^' the lead implemented to include fixation arrangements in accordance with the present invention;

Figure 8 A is a magnified view of a further embodiment of a lead having an electrode, the. lead implemented to include fixation arrangements in accordance with the present invention; Figure 8B is an end view of the embodiment illustrated in Figure 8 A;

Figure 9A is a magnified view of another embodiment of a lead having an electrode, the lead implemented to include a fixation arrangement in accordance with the present invention;

Figure 9B is an end view of the embodiment illustrated in Figure 9 A; Figure 9C is a magnified view of another embodiment of a lead having an electrode, the lead implemented to include a fixation arrangement in accordance with the present invention;

Figure 9D is an end view of the embodiment illustrated in Figure 9C;

Figure 9E is a magnified view of another embodiment of a lead having an electrode, the lead implemented to include a fixation arrangement in accordance with the present invention;

Figure 9F is an end view of the embodiment illustrated in Figure 9E; Figure 9G is a magnified sectional view of another embodiment of a lead implemented to include a fixation arrangement in accordance with the present invention;

Figures 10 A, 10B, IOC and 10D are sectional views of various tines in accordance with the present invention; Figure 11 illustrates a lead in accordance with the present invention, inserted in a dissected subcutaneous path leading from the can, where an offset helical electrode/fixation element is illustrated fixed to the tissue;

Figure 12 is a plan view of a lead enclosed within a sheath prior to deployment of a fixation element in accordance with the present invention; Figure 13 is a magnified view of one embodiment of a lead having an electrode, the lead implemented to include a fixation arrangement in accordance with the present invention;

Figure 14 is a magnified end view of the embodiment of Figure 13; Figure 15 is a magnified view of a further embodiment of a lead having an electrode, the lead implemented to include a fixation arrangement in accordance with the present invention; and

Figure 16 is a magnified end view of the embodiment of Figure 15. While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail below. It is to be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS In the following description of the illustrated embodiments, references are made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized, and structural and functional changes may be made without departing from the scope of the present invention. A device employing an implantable lead implemented in accordance with the present invention may incorporate one or more of the features, structures, methods, or combinations thereof described herein below. For example, leads for a subcutaneous cardiac monitor or stimulator may be implemented to include one or more of the features and/or processes described below. It is intended that such a device or method need not include all of the features and functions described herein, but may be implemented to include selected features and functions that, in combination, provide for unique structures and/or functionality.

Implantable subcutaneous devices and methods in accordance with the present invention employ a lead and/or electrode for cardiac monitoring and/or stimulation. The lead and/or electrode includes one or more fixation elements, for example, expandable elements, porosity, helical fixation elements, grooves, ridges, tines, tines with barbs, spring-loaded tines, flexible or collapsible tines, and other fixation mechanisms configured to actively and/or passively secure one or both of the electrode or body of the lead in subcutaneous non- intrathoracic tissue acutely, chronically, or acutely and chronically.

A method ofimplanting subcutaneous leads according to the present invention involves providing a lead comprising a lead body, an electrode, and one or more fixation elements, and securing one or both of the lead body and the electrode to subcutaneous non- intrathoracic tissue at one or more fixation sites using the fixation elements. The method may involve use of a delivery device, such as a sheath, for lead delivery to a subcutaneous non-intrathoracic implant site. In general terms, an implantable lead implemented in accordance with the present invention may be used with a subcutaneous cardiac monitoring and/or stimulation device. One such device is an implantable transthoracic cardiac monitoring and/or stimulation (ITCS) device that may be implanted under the skin in the chest region of a patient. The ITCS device may, for example, be implanted subcutaneously such that all or selected elements of the device are positioned on the patient's front, back, side, or other body locations suitable for monitoring cardiac activity and delivering cardiac stimulation therapy. It is understood that elements of the ITCS device may be located at several different body locations, such as in the chest, abdominal, or subclavian region with electrode elements respectively positioned at different regions near, around, in, or on the heart.

The primary housing (e.g., the active or non-active can) of the ITCS device, for example, may be configured for positioning outside of the rib cage at an intercostal or subcostal location, within the abdomen, or in the upper chest region (e.g., subclavian location, such as above the third rib), hi one implementation, one or more electrodes may be located on the primary housing and/or at other locations about, but not in direct contact with the heart, great vessel or coronary vasculature. In another implementation, one or more leads, incorporating electrodes may be located in direct contact with the heart, great vessel or coronary vasculature, such as via one or more leads implanted by use of conventional transvenous delivery approaches. In another implementation, for example, one or more subcutaneous electrode subsystems or electrode arrays may be used to sense cardiac activity and deliver cardiac stimulation energy in an ITCS device configuration employing an active can or a configuration employing a non-active can. Electrodes may be situated at anterior and/or posterior locations relative to the heart.

Referring now to Figures 1 A and IB of the drawings, there is shown a configuration of an ITCS device implanted in the chest region of a patient at different locations by use of a dissection tool. In the particular configuration shown in Figures 1A and IB, the ITCS device includes a housing 102 within which various cardiac monitoring, detection, processing, and energy delivery circuitry may be housed. The housing 102 is typically configured to include one or more electrodes (e.g., can electrode and/or indifferent electrode). Although the housing 102 is typically configured as an active can, it is appreciated that a non-active can configuration may be implemented, in which case at least two electrodes spaced apart from the housing 102 are employed. An ITCS system according to this approach is distinct from conventional approaches in that it is preferably configured to include a combination of two or more electrode subsystems that are implanted subcutaneously. In the configuration shown in Figures 1 A and IB, a subcutaneous electrode 104 may be positioned under the skin in the chest region and situated distal from the housing 102. The subcutaneous and, if applicable, housing electrode(s) may be positioned about the heart at various locations and orientations, such as at various anterior and/or posterior locations relative to the heart. The subcutaneous electrode 104 is electrically coupled to circuitry within the housing 102 via a lead assembly 106. One or more conductors (e.g., coils or cables) are provided within the lead assembly 106 and electrically couple the subcutaneous electrode 104 with circuitry in the housing 102. One or more sense, sense/pace or defibrillation electrodes may be situated on the elongated structure of the electrode support, the housing 102, and/or the distal electrode assembly (shown as subcutaneous electrode 104 in the configuration shown in Figures 1A and IB).

In one configuraαon, the lead assembly 106 is generally flexible. In another configuration, the lead assembly 106 is constructed to be somewhat flexible, yet has an elastic, spring, or mechanical memory that retains a desired configuration after being shaped or manipulated by a clinician. For example, the lead assembly 106 may incorporate a gooseneck or braid system that may be distorted under manual force to take on a.desired shape. In this manner, the lead assembly 106 may be shape-fit to accommodate the unique anatomical configuration of a given patient, and generally retains a customized shape after implantation. Shaping of the lead assembly 106 according to this configuration may occur prior to, and during, ITCS device implantation.

In accordance with a further configuration, the lead assembly 106 includes a rigid electrode support assembly, such as a rigid elongated structure that positionally stabilizes the subcutaneous electrode 104 with respect to the housing 102. In this configuration, the rigidity of the elongated structure maintains a desired spacing between the subcutaneous electrode 104 and the housing 102, and a desired orientation of the subcutaneous electrode 104/housing 102 relative to the patient's heart. The elongated structure may be formed from a structural plastic, composite or metallic material, and includes, or is covered by, a biocompatible material. Appropriate electrical isolation between the housing 102 and the subcutaneous electrode 104 is provided in cases where the elongated structure is formed from an electrically conductive material, such as metal.

In one configuration, the rigid electrode support assembly and the housing 102 define a unitary structure (i.e., a single housing/unit). The electronic components and electrode conductors/connectors are disposed within or on the unitary ITCS device housing/electrode support assembly. At least two electrodes are supported on the unitary structure near opposing ends of the housing/electrode support assembly. The unitary structure may have, for example, an arcuate or angled shape.

According to another configuration, the rigid electrode support assembly defines a physically separable unit relative to the housing 102. The rigid electrode support assembly includes mechanical and electrical couplings that facilitate mating engagement with corresponding mechanical and electrical couplings of the housing 102. For example, a header block arrangement may be configured to include both electrical and mechanical couplings that provide for mechanical and electrical connections between the rigid electrode support assembly and housing 102. The header block arrangement may be provided on the housing 102 or the rigid electrode support assembly or both. Alternatively, a mechanical/electrical coupler may be used to establish mechanical and electrical connections between the rigid electrode support assembly and the housing 102. In such a configuration, a variety of different electrode support assemblies of varying shapes, sizes, and electrode configurations may be made available for physically and electrically connecting to a standard ITCS device. It is noted that the electrodes and the lead assembly 106 may be configured to assume a variety of shapes. For example, the lead assembly 106 may have a wedge, chevron, flattened oval, or a ribbon shape, and the subcutaneous electrode 104 may include a number of spaced electrodes, such as an array or band of electrodes. Moreover, two or more subcutaneous electrodes 104 may be mounted to multiple electrode support assemblies 106 to achieve a desired spaced relationship amongst the subcutaneous electrodes 104. Accordingly, subcutaneous leads of the present invention may be shaped appropriately for specific electrodes or families of electrodes and electrode support assemblies.

Referring now to Figure 2, an ITCS system 200 is illustrated which includes a can 250 with a lead 241 inserted into a subcutaneous dissection path 220. The lead 241 includes an electrode 230 and a lead body 240. The electrode 230 is here illustrated at the distal end of the lead body 240. The subcutaneous dissection path 220 lies within subcutaneous tissue of a patient as illustrated in Figures 1 A and IB. The lead 241 may be inserted into the subcutaneous dissection path 220 by itself, or may also be inserted with use of a sheath 320 as illustrated in Figure 3 A.

In Figure 3A, a proximal end of the lead body 240 extends from the sheath 320, with the electrode 230 enclosed within the lumen of the sheath 320. The electrode 230 is illustrated that includes fixation elements 232 and 234 respectively provided at distal and proximal ends of the electrode 230. It should be understood that any number of such fixation elements may be employed to fix the electrode 230 within subcutaneous tissue. The fixation elements 232 and 234 may include, for example, an expandable fixation mechanism, such as a spongy material that is preferably, but not necessarily, compressed within the lumen of the sheath 320 during delivery. According to one delivery approach, the lead 241 may be inserted into the dissection path, such as dissection path 220 shown in Figure 2, while inside the sheath 320. After positioning the sheath 320 at the desired location within subcutaneous tissue, the sheath 320 may be retracted or otherwise separated from the lead 241. Retracting the sheath 320 from the electrode 230 and the lead body 240 permits the fixation elements 232 and 234 to expand and affix the electrode 230 within the subcutaneous tissue.

A suitable material for constructing the fixation elements 232 and 234 is Scleral sponge. However, the fixation elements 232 and 234 may be constructed from any implantable material capable of expansion. Expansion of the fixation elements 232 and 234 may occur due to their release from the sheath 320, from uptake of body fluid, from an injected material, or other means of expansion. For example, a fluid may be injected into an expandable balloon fixation element with a one-way valve or stopper.

Other embodiments of expanding fixation elements are illustrated in Figures 3B and 3C. In Figure 3B an expanding collar 330 and an expanding lead portion 340 are illustrated in their pre-expansion configuration. The expanding collar 330 and lead portion 340 may, for example, be components made of a mixture of a biocompatible polymer and a water- soluble additive. By way of illustration, silicone rubber and a water-soluble additive such as glycerol represent one combination of materials useful for producing the expanding collar 330 and the expanding lead portion 340.

This combination of materials expands after implantation due to water ingression via osmosis. Utilizing a polymer/additive composition, the absorbed water supplied by the body's aqueous environment penetrates the polymer and dissolves isolated additive particles to provide component expansion. The subsequent reaction forces generated within the polymeric phase eventually balances the osmotic forces so that destructive expansion does not occur. The expanded tip or collar 330 may itself provide a press-fit within the pocket, ensuring fixation. In addition, by using other compositions, the water pockets may combine within the component sufficiently to create pores that communicate with the component surface, which promotes tissue ingrowth. Figure 3C illustrates an expanded collar 350 and an expanded lead portion 360.

After implantation, collar 330 and lead portion 340 (shown in Figure 3B) expand, and transform into expanded collar 350 and expanded lead portion 360. The expanded collar 350 and portion 360 may be employed in combination and/or by themselves, to fix the lead 241 into tissue.

Turning now to Figure 4, there is illustrated an embodiment of the lead 241 that includes an electrode 230 provided with another fixation arrangement. The lead 241 is shown to include the electrode 230 now having tines 410, 420, 430, 440, 450, and 460 projecting outwardly from the body of the electrode 230/lead body 240. Also illustrated are a number of diagonal grooves 470, 471, 472, 473, and 474.

The tines 410-460 are shown biased away from the lead body 240 by, for example, manufacturing the tines 410-460 using a mechanically elastic material having spring-like qualities such as, for example, metal or plastic. The tines 410-460 may be angled away and proximally oriented, as illustrated in Figure 4, to allow the lead 241 to be easily inserted into the dissection path in a distal direction, but resist being pulled out in a proximal direction. The tines 410-460 provide for acute fixation of the lead 241 into subcutaneous tissue. After placement and acute fixation of the lead 241 within subcutaneous tissue, the grooves 470-474 provide regions for promoting tissue ingrowth, which chronically fixes the lead 241 within the subcutaneous tissue. The grooves 470-474 are denoted by a series of parallel lines oriented diagonally relative to a longitudinal axis of the lead body 240. It is contemplated that any number of grooves may be implemented at any angle or at varying angles. For example, a crosshatched pattern of grooves 510, as is illustrated in Figure 5, may be incorporated to promote tissue ingrowth after placement of the lead 241 within subcutaneous tissue. The grooves 470-474 may be of any suitable size, shape, depth or spacing.

As illustrated in Figure 6, one or more ridges 610 may be used in combination with, or in lieu of, grooves for chronic tissue purchase. The ridges 610 may be configured to provide for chronic fixation of the lead body 240 resulting from tissue ingrowth. Both grooves 510 (Figure 5) and ridges 610 may also provide a degree of acute fixation, depending on the size of the grooves 510 or ridges 610. Acutely, the grooves 510 or ridges 610 would provide an initial purchase with the tissue. As time progresses, the initial immature encapsulation will constrict, resulting in a more firm purchase on the lead 241. As is further illustrated in Figure 6, a plurality of tines 620, 630, 640, 650, 660, and 670 may be used in combination with other fixation techniques for purposes of acutely fixing the lead body 240 and/or a lead electrode, as described earlier. Features such as the plurality of tines 620, 630, 640, 650, 660, and 670 may be located on the lead body 240 and/or the electrode 230. The tines 620-670 and/or the ridges 610 and/or grooves may be used in various combinations along with other acute fixation techniques known in the art, such as, for example, a suture attachment point (not shown) on the lead 241.

Referring now to Figure 7, another fixation arrangement in accordance with the present invention is illustrated. According to this embodiment, the fixation arrangement includes one or more textured surfaces or regions 710 on the lead body 240 and/or an electrode 230 of the lead 241. The textured surface(s) 710 may be employed as a sole chronic fixation method or in combination with other chronic fixation arrangements, such as a set of grooves 720 as is depicted in Figure 7.

The textured surface 710 promotes tissue ingrowth to provide for chronic fixation of the lead body 240 into subcutaneous tissue. The textured surface 710 may be, for example, a porous region of the lead body 240, a coating having surface irregularities, dimples molded into the lead body 240 and/or a lead electrode 230, surface treatments from manufacturing processes such as sanding or scratching, or other suitable texturing.

Generally at least one acute fixation mechanism is employed in combination with chronic fixation mechanism, to allow sufficient time for the fixing of the chronic fixation mechanism into the subcutaneous tissue. An appropriate acute fixation mechanism is, for example, a suture placed at the distal end of the lead 241.

According to other fixation arrangements similar to those described above, and with reference to Figure 7, the lead body 240 and/or the electrode 230 may be configured to incorporate tissue adhesion sites that facilitate chronic fixation of the lead body 240 and/or electrode 230 in subcutaneous tissue. For example, the adhesion sites may include voids in the sleeve of the lead body 240 at one or more locations of the sleeve. The adhesion sites may include exposed portions of one or more electrodes 230 or other exposed portions of the lead 241 insulation or covering.

According to another configuration, the adhesion sites may include a structure having a porous surface that promotes subcutaneous tissue in-growth or attachment at the adhesion sites. For example, a metallic annular structure may be disposed at the adhesion site. A metallic ring, for example, having porous surface characteristics may be employed to promote cellular adhesion at the adhesion site. The annular structure may incorporate the electrode 230 or be separate from the electrode 230.

In accordance with a further configuration, the adhesion sites may include a material that promotes subcutaneous tissue in-growth or attachment at the adhesion sites. For example, the bulk outer sleeve of the lead body 240 may be constructed that includes a first polymer material that substantially prevents tissue in-growth. Selective portions of the lead body 240 may include adhesion sites formed using a second polymer material that promotes tissue in-growth or attachment between the adhesion sites and subcutaneous tissue contacting the adhesion sites. The second polymer material may, for example, have a porosity, pore sizes or distribution of pore sizes that differ from that of the first polymer material. By way of further example, the second polymer material may differ in terms of hydrophobicity relative to the first polymer material.

In one particular configuration, the first polymer material may include a first type of PTFE (polytetrafluoroethylene), and the second polymer material of the adhesion sites may include a second type of PTFE. In one particular arrangement, the first type of PTFE includes a first type of ePTFE (expanded polytetrafluoroethylene), and the second type of PTFE includes a second type of ePTFE. The second type of ePTFE preferably differs from the first type of ePTFE in terms of one or more of porosity, pore sizes or distribution of pore sizes. Additional details of fixation approaches involving surface texturing, selective material use, and other arrangements that facilitate lead/electrode fixation via tissue ingrowth are disclosed in commonly owned U.S. Patent Application Serial No. 10/004,708 (GUID.031US01) filed December 4, 2001 and entitled "Apparatus and Method for Stabilizing an Implantable Lead," which is hereby incorporated herein by reference.

Now referring to Figures 8 A and 8B, details of acute fixation elements according to another embodiment of the present invention are shown. A lead 800 is illustrated that includes a plurality of tines 810, 820, 830, 840, 845 (Figure 8B), 850, 860, 870, 880, and 890 (Figure 8 A). The tines 810-890 are shown disposed regularly with 90 degree circumferential placement, and regularly spaced along the length of the lead 800. However, other angles, regularity or irregularity, or number of tines may be employed in accordance with this embodiment. The tines 810-890 are shown, in this illustrative example, to be curved as they extend from the body of the lead 800. Curvature may assist in facilitating acute fixation by providing ease of movement of the lead 800 in a first direction (e.g., axial displacement in a distal direction), while helping to set the tines into tissue in response to movement in a second direction (e.g., axial displacement in a proximal direction). It is contemplated that the tines may be straight, or have a curvature tending away from or toward the body of the lead 800. Tines configured in accordance with the present invention may also be curved in more than one plane, as is illustrated in Figures 9 A and 9B. A lead 900 (lead and/or electrode) is shown that includes tines 910, 920, 930, 935 (Figure 9B), 940, 950, and 960 (Figure 9A). As shown, the tines 910-960 are curved upward and away from the lead 900 relative to a longitudinal axis of the lead 900. The tines 910-960 are also curved around the circumference of the body of the lead 900 with respect to a second plane of reference.

The complex curvature illustrated in Figures 9A and 9B may be advantageous for optimally placing and fixing the lead 900 within subcutaneous tissue. This complex curvature provides for ease of inserting and withdrawing of the lead 900 when the lead 900 is rotated in a first direction. If the lead 900 is not rotated, the tines 910-960 set into the tissue. Further, if the lead 900 is rotated in the counter direction, the tines 910-960 may be forced into subcutaneous tissue.

Another tine configuration that employs complex curvature is illustrated in Figures 9C and 9D for optimally placing and fixing the lead 900 within subcutaneous tissue. This complex curvature provides for fixation from proximal displacement, and from rotation of the lead 900. Tines 921, 923, 931, 933, 951, and 953 set into the tissue due to their spring bias outwardly and upwardly from the lead 900. Placement of this type of lead fixation may be accomplished by direct distal insertion, to compress the tines 921, 923, 931, 933, 951, and 953 during placement and upon release of distal motion, the tines 921, 923, 931, 933, 951, and 953 spring Outwardly from the lead 900 for fixation. A further tine configuration that employs complex curvature is illustrated in Figures

9E and 9F for optimally placing and fixing the lead 900 within subcutaneous tissue. This complex curvature provides for fixation from both proximal and distal displacement, and from rotation of the lead 900. Tines 922, 932, 942, 952, 962, and 972 set into the tissue due to their spring bias outwardly and upwardly from the lead 900. Placement of this type of lead fixation may be accomplished by utilization of a sheath, as described earlier, to compress the tines 922, 932, 942, 952, 962, and 972 during placement, and upon removal of the sheath, the tines 922, 932, 942, 952, 962, and 972 spring outwardly from the lead 900 for fixation.

Figure 9G is a magnified sectional view of another embodiment of a lead implemented to include a fixation arrangement in accordance with the present invention. Tines 973 and 974 set into the tissue due to their spring^' bias outwardly and upwardly from the lead 900. Placement of this type of lead fixation may be accomplished by utilization of • a sheath, as described earlier, to compress the tines 973 and 974 during placement, and upon removal of the sheath, the tines 973 and 974 spring outwardly from the lead 900 for fixation. Figures 10A, 10B, 10C and 10D illustrate various shapes for tines in accordance . with the present invention. In Figure 10 A, a tine 1010 is shown projecting from the lead 900. The tine 1010 has a single tip 1080. The tine 1010 is shaped to spring away from the lead 900 body.

For descriptive ease, consider a lead in the plane of Figures 10 A, 10B, 10C and 10D, with the lead 900 moving from left to right in the plane of the figures. If the lead 900 were inserted, in this drawing from the left to the right, the tine 1010 would tend to collapse into the lead 900 and allow forward progress of the lead 900. If the lead 900 were to be pulled from right to left in Figure 10 A, the tine 1010 would tend to set into tissue by the single tip 1080. Similarly to the tine of Figure 10A, a tine 1020 of Figure 10B would also flex and set under the same movement. However, the tine 1020, not as substantial as the tine 1010 of Figure 10 A, would more easily collapse and compress under left to right motion, and may provide less resistance to right to left motion.

Referring now to Figure 10C, a tine 1030 is illustrated with a first point 1050 and a second point 1040. The shape of the tine 1030, along with the second point 1040, creates a barb 1060. The barb 1060, similar to a fishhook barb, provides for not only resistance to right to left motion, but also for resistance to further left to right motion after being set. This arrangement provides for ease of insertion in a left to right direction, a resistance to right to left movement, and subsequently also provides resistance to further left to right movement after being set.

Referring to Figure 10D, a straight tine 1012 is illustrated perpendicularly projecting from the lead 900 body. The straight tine 1012 may be compressed and/or spring biased in the lumen of a sheath (such as, for example, the sheath 320 in Figure 3 A) during delivery of the lead 900, such that the straight tine 1012 sets into tissue when the sheath is removed. In another embodiment, the rigidity of the straight tine 1012 may be designed such that a set level of resistance is provided by the straight tine 1012 when it is moved within tissue. By adjusting the rigidity, the level of fixation of the lead 900, and the associated ease of insertion/relocation, may be predetermined by design. Rigidity may be altered by material selection, geometry, of other means known in the art.

Referring now to Figure 11, an ITCS system 200 is illustrated which includes a can 250 with a lead 241 inserted into a dissection path 220. The lead 241 includes an electrode 230, here illustrated at the distal end of the lead body 240. The subcutaneous dissection path 220 lies within subcutaneous tissue of a patient as illustrated in Figures 1 A and IB. An offset helix 260 is employed as a fixation element useable to fix the lead 241 into tissue in accordance with the preβent invention. Typically, the helix 260 is configured to define all or at least part of the electrode 230. Figure 12 illustrates the lead 241 inserted into the tear-away sheath 320 as described with an earlier embodiment. After placing the lead 241 in subcutaneous tissue, the sheath 320 is retracted from the subcutaneous tunnel, typically in a peel-away fashion. The lead 241 may be fixed into the tissue by rotating the lead 241 as will be described in further detail below. " Figures 13 and 14 show a plan view and end view respectively of an embodiment of the present invention. In Figure 13, a helical coil 260 may be used as a fixation element to fix the lead body 240 into tissue when the electrode 230 is positioned in a desired location. The helical coil 260 is attached to the distal end of the lead body 240 at attachment point 262. Rotation of the lead body 240 causes rotation of the helical coil 260, thereby rotating sharp end 400.

Although helical coil 260 is illustrated having uniform pitch, cylindrical cross- section, constant thickness of coil, it is contemplated that any helical or screw-like structure may be used in accordance with the present invention. The helix may be of non-uniform and/or tapering cross-section; the pitch may be non-uniform; and the shape and thickness of the coil may be varied without departing from the scope of the present invention.

As the lead 241 is rotated, the sharp end 400 contacts the wall of the dissected tissue path and penetrates into subcutaneous tissue. As the lead 241 is further rotated, the sharp . end 400 burrows through the tissue, repeatedly penetrating the wall and progressing forward as the winding of the helical coil 260 dictates. This effectively screws the helical coil 260 into the wall of the tissue, thus fixing the lead 241.

In the embodiment illustrated in Figures 13 and 14, the helical coil 260 is seen to be larger in diameter than the lead body 240. An advantage of employing the helical coil 260 that is larger than the lead body 240 is the assurance that as the lead lies within the dissected tissue tunnel, the sharp end 400 penetrates the tunnel wall and provide fixation when rotated. If the helical coil 260 were the same size or smaller than the lead body 240 diameter, the lead body may prevent the sharp end 400 from initiating penetration unless the lead body 240 is pushed distally along the dissection tunnel until penetration occurs. This pushing of the lead may cause the electrode 230 to be moved distally from an optimum fixation location.

Referring now to Figures 15 and 16, a plan view and end view respectively of another embodiment of the present invention is illustrated. In Figure 15, an offset helical coil 661 may be used as a fixation element to fix the lead body 240 into tissue when the electrode 230 is positioned in a desired location. The offset helical coil 661 is attached to the distal end of the lead body 240 at attachment point 662. Rotation of the lead body 240 causes rotation of the offset helical coil 661, rotating sharp end 600.

As the lead body 240 is rotated, the sharp end 600 contacts the wall of the dissected tissue path and penetrates into subcutaneous tissue. As the lead body 240 is further rotated, the sharp end 600 burrows through the tissue, repeatedly penetrating the wall and progressing forward as the winding of the offset helical coil 661 dictates. This effectively screws the offset helical coil 661 into the wall of the tissue, thus fixing the lead 241.

In the embodiment illustrated in Figures 15 and 16, as best seen in Figure 16, the offset helical coil 661 is seen to have an offset central axis relative to the longitudinal axis of the lead body 240. An advantage of employing the offset helical coil 661 offset from the lead body 240 is the assurance that as the lead lies within the dissected tissue tunnel, the sharp end 600 penetrates the tunnel wall and provides fixation when rotated.

Coils 260 and 661 may be manufactured using a spring material such as, for example, metal, such that coils 260 and 661 deform within the sheath 320 when being advanced to their fixation locations. Upon removal of the sheath 320, coils 260 and 661 spring into their larger or offset configurations to affect fixation into tissue. Coils 260 and 661 may also be manufactured using a shape memory alloy such as, for example, Nitinol, such that coils 260 and 661 have a first, non-penetrating shape, when being advanced through the dissection path. Upon being subjected to body temperature or artificially heated, coils 260 and 661 return to a shape such as described above to affect fixation. It should be understood that any number, type, or combination of fixation elements have, been contemplated, and that the number, types, and combinations presented above are by way of example only. Various modifications and additions can be made to the preferred embodiments discussed hereinabove without departing from the scope of the present invention. Accordingly, the scope of the present invention should not be limited by the particular embodiments described above, but should be defined only by the claims set forth below and equivalents thereof.

Claims

CLAIMSWhat is claimed is:

1. An implantable lead arrangement, comprising: a lead body; a cardiac electrode supported by the lead body, the cardiac electrode configured for subcutaneous non-intrathoracic placement within a patient; and a plurality of fixation elements provided on one or both of the cardiac electrode and the lead body, the fixation elements configured to secure the lead arrangement in subcutaneous non-intrathoracic tissue.

2. The lead arrangement according to claim 1, wherein the plurality of fixation elements comprise tines.

3. The lead arrangement according to claim 2, wherein the tines comprise barbs.

4. The lead arrangement according to claim 2, wherein a projection of a longitudinal axis of the tines is non-parallel with respect to a longitudinal axis of the lead body.

5. The lead arrangement according to claim 1, wherein the plurality of fixation elements comprise tines formed from a material having a spring memory, the tines situated on the lead arrangement to permit axial displacement of the lead arrangement in a distal direction and to be set in the subcutaneous non-intrathoracic tissue in response to axial displacement of the lead arrangement in a proximal direction.

6. The lead arrangement according to claim 1 , wherein the plurality of fixation elements comprise collapsible tines.

7. The lead arrangement according to claim 6, comprising a sheath having a lumen dimensioned to at least partially collapse the collapsible tines while permitting axial displacement of the lead arrangement within the lumen.

8. The lead arrangement according to claim 7, wherein the sheath comprises a longitudinal pre-stress line arrangement to facilitate sheath separation during retraction of ^' the sheath from the patient.

9. The lead arrangement according to claim 1, wherein the plurality of fixation elements comprise tines biased radially outward from the lead arrangement, the tines oriented on the lead arrangement to permit rotation of the lead arrangement in a first direction and to resist rotation of the lead arrangement in a second direction.

10. The lead arrangement according to claim 1, wherein at least one fixation element of the plurality of fixation elements has a fixation element cross-sectional , diameter, and wherein the fixation element cross-sectional diameter is larger than a cross- sectional diameter of the lead body.

11. The lead arrangement according to claim 10, wherein the at least one fixation element of the plurality of fixation elements comprises a helical coil.

12. The lead arrangement according to claim 11, wherein the helical coil is configured to be compressible while in a non-deployed configuration, a cross-sectional diameter of the helical coil substantially equal to or less than the cross-sectional diameter of the lead body while in the non-deployed configuration.

13. The lead arrangement according to claim 1 , wherein the lead body has a lead longitudinal axis and at least one fixation element of the plurality of fixation elements has a fixation element longitudinal axis, and wherein the lead longitudinal axis is non-coincident with respect to the fixation element longitudinal axis.

14. The lead arrangement according to claim 1 , wherein at least one fixation element of the plurality of fixation elements is part of the electrode.

15. The lead arrangement according to claim 1 , wherein: the lead body comprises a longitudinal axis; and at least one fixation element of the plurality of fixation elements comprises a longitudinal axis aligned substantially perpendicular to the longitudinal axis of the lead body.

16. The lead arrangement according to claim 1, wherein at least one fixation element of the plurality of fixation elements is configured to actively secure the lead body or electrode in subcutaneous non-intrathoracic tissue.

17. The lead arrangement according to claim 1, wherein at least one fixation element of the plurality of fixation elements is configured to expandably secure one or both of the cardiac electrode and the lead body in subcutaneous non-intrathoracic tissue.

18. A lead arrangement according to claim 17, comprising at least one fixation element of the plurality of fixation elements configured to acutely secure one or both of the lead body and the cardiac electrode to the subcutaneous non-intrathoracic tissue.

19. The lead arrangement according to claim 17, wherein the lead arrangement comprises a sheath having a longitudinal pre-stress line arrangement to facilitate sheath separation during retraction of the sheath from the patient, the sheath comprising a lumen dimensioned to at least partially collapse the at least one expandable fixation element while permitting axial displacement of the lead arrangement within the lumen.

20. The lead arrangement according to claim 17, wherein the at least one . expandable fixation element is provided on the cardiac electrode.

21. The lead arrangement according to claim 17, wherein the at least one expandable fixation element comprises a sponge.

22. The lead arrangement according to claim 17, wherein the at least one expandable fixation element comprises a scleral sponge.

23. The lead arrangement according to claim 1 , wherein the plurality of fixation elements comprise a plurality of sponges arranged in a spaced relationship.

24. The lead arrangement according to claim 1, wherein the plurality of fixation elements comprise an expandable portion of the lead body.

25. The lead arrangement according to claim 24, wherein the expandable portion of the lead body comprises an additive in a polymer.

26. The lead arrangement according to claim 25, wherein the additive comprises glycerol.

27. The lead arrangement according to claim 24, wherein the expandable portion of the lead body comprises an expandable polymer.

28. The lead arrangement according to claim 27, wherein the expandable polymer comprises hydrogel.

.

29. The lead arrangement according to claim 1, wherein at least one fixation element of the plurality of fixation elements comprises an expandable collar coupled to the lead body.

30. The lead arrangement according to claim 29, wherein the expandable collar comprises an additive in a polymer.

31. The lead arrangement according to claim 30, wherein the additive comprises glycerol.

32. A lead arrangement according to claim 1, wherein at least one fixation element of the plurality of fixation elements comprises an expandable portion provided on the implantable lead arrangement, the expandable portion configured to provide pores that promote tissue ingrowth for chronic fixation.

33. A lead arrangement according to claim 32, comprising at least one fixation element of the plurality of fixation elements configured to acutely secure one or both of the lead body and the cardiac electrode to the subcutaneous non-intrathoracic tissue.

34. The lead arrangement according to claim 32, wherein the expandable portion comprises first and second additives, the first additive configured to provide expansion and the second additive configured to provide the pores.

35. The lead arrangement according to claim 32, wherein the expandable portion . comprises a polymer having first and second additive concentrations, the first additive concentration configured to provide expansion and the second additive concentration configured to provide the pores.

36. The lead arrangement according to claim 1, wherein at least one fixation element of the plurality of fixation elements comprises a textured surface configured to promote tissue ingrowth.

37. The lead arrangement according to claim 36, wherein the textured surface comprises ridges.

38. The lead arrangement according to claim 36, wherein the textured surface comprises grooves.

39. A method, comprising: providing a lead comprising a lead body, a cardiac electrode, and a plurality of fixation elements; and manipulating at least one of the lead body, the cardiac electrode, and one or more of the plurality of fixation elements, wherein the plurality of fixation elements are configured to be securable in subcutaneous non-intrathoracic tissue.

40. The method according to claim 39, wherein the plurality of fixation elements comprise tines that are configured to fixedly engage the subcutaneous non- intrathoracic tissue.

41. The method according to claim 39, wherein a position or an orientation of the plurality of fixation elements facilitates axial displacement of the lead in a distal direction and resists axial displacement of the lead in a proximal direction.

42. The method according to claim 39, wherein a position or an orientation of the plurality of fixation elements facilitates axial displacement of the lead in a distal direction and resists rotational displacement of the lead in both clockwise and counterclockwise directions.

43. The method according to claim 39, wherein one or more of the plurality of fixation elements is configured to resist rotation of the lead in a first direction and permit rotation of the lead in a second direction.

44. The method according to claim 39, comprising: providing a removable sheath having a lumen; and modifying a position or an orientation of at least some of the plurality of fixation elements when the lead is within the lumen.

45. The method according to claim 44, wherein removing the lead from the sheath comprises enabling a plurality of fixation elements for passive engagement.

46. The method according to claim 44, comprising returning the at least some of the plurality of fixation elements to an initial position or orientation when the at least some of the plurality of fixation elements are advanced beyond, or retracted from, the lumen of the sheath.

47. The method according to claim 39, wherein the lead is configured such that rotating the lead in a first direction engages a plurality of fixation elements, and rotating the lead in a second direction resists disengagement of the plurality of fixation elements.

48. The method according to claim 39, wherein the plurality of fixation elements are configured to permit longitudinal advancement of the lead in a distal direction and to resist longitudinal advancement of the lead in a proximal direction.

49. The method according to claim 39, wherein the plurality of fixation elements comprise at least one acute fixation element configured to acutely securing one or both of the lead body and the cardiac electrode, and at least one chronic fixation element configured to chronically securing one or both of the lead body and the cardiac electrode.

50. The method according to claim 49, wherein the at least one acute fixation element comprises a helical coil configured to acutely secure the one or both of the lead body and the cardiac electrode to the subcutaneous non-intrathoracic tissue.

51. The method according to claim 49, wherein the at least one acute fixation element comprises a suture configured to acutely secure the one or both of the lead body and the cardiac electrode to the subcutaneous non-intrathoracic tissue.

52. The method according to claim 49, wherein the at least one chronic fixation element comprises a portion of the lead configured to promote tissue ingrowth between the one or both of the lead body and the cardiac electrode and the subcutaneous non- intrathoracic tissue.

53. The method according to claim 49, wherein the at least one acute fixation element comprises a helical fixation element configured to affix in the_. subcutaneous non- intrathoracic tissue when the lead is rotated.

54. A method, comprising: providing a lead comprising a lead body, a cardiac electrode, and an expandable fixation element; and expanding the expandable fixation element, the expanded fixation element configured to secure the lead arrangement in subcutaneous non-intrathoracic tissue.

55. The method according to claim 54, wherein the expandable fixation element expands to an effective diameter larger than the diameter of the lead body.

56. The method according to claim 54, wherein the expandable fixation element comprises one or more expandable fixation elements that are configured to expand to fixedly engage the subcutaneous non-intrathoracic tissue at one or more fixation sites.

57. The method according to claim 54, comprising: providing a sheath having a lumen; advancing the lead through the sheath; and removing the sheath from the lead.

58. The method according to claim 57, wherein removing the sheath comprises longitudinally splitting the sheath.

59. The method according to claim 57, wherein removing the sheath comprises enabling at least one fixation element of the one or more expandable fixation elements.

60. The method according to claim 57, wherein advancing the lead through the sheath comprises modifying a position or an orientation of at least one expandable fixation element of the one or more expandable fixation elements.

61. The method according to claim 57, wherein advancing the lead through the sheath comprises compressing at least one expandable fixation element of the one or more expandable fixation elements.

62. An implantable lead, comprising: a lead body; a cardiac electrode supported by the lead body, the cardiac electrode configured for subcutaneous non-intrathoracic placement within a patient; and an expandable fixation element provided on the implantable lead, the expandable fixation element configured to expandably secure one or both of the cardiac electrode and the lead body in subcutaneous non-intrathoracic tissue.

63. The lead according to claim 62, wherein the expandable fixation element is provided on the cardiac electrode.

64. The lead according to claim 62, wherein the expandable fixation element comprises a sponge.

65. The lead according to claim 62, wherein the expandable fixation element comprises a scleral sponge.

66. The lead according to claim 62, wherein the expandable fixation element comprises a plurality of sponges arranged in a spaced relationship.

67. The lead according to claim 62, wherein the expandable fixation element comprises an expandable portion of the lead body.

68. The lead according to claim 67, wherein the expandable portion of the lead body comprises an additive in a polymer.

69. The lead according to claim 68, wherein the additive comprises glycerol.

70. The lead according to claim 67, wherein the expandable portion of the lead body comprises an expandable polymer.

71. The lead according to claim 70, wherein the expandable polymer comprises hydrogel.

72. The lead according to claim 62, wherein the expandable fixation element comprises an expandable collar coupled to the lead body.

73. The lead according to claim 72, wherein the expandable collar comprises an additive in a polymer.

74. The lead according to claim 73, wherein the additive comprises glycerol.

75. The lead according to claim 62, further comprising a delivery apparatus configured to introduce the lead to a desired subcutaneous non-intrathoracic location within the patient.

76. The lead system according to claim 75, wherein a lumen of the delivery apparatus is dimensioned to compress the expandable fixation element while permitting axial displacement of the lead within the lumen.

77. The lead system according to claim 75, wherein the delivery apparatus comprises a sheath having a longitudinal pre-stress line arrangement to facilitate sheath separation during retraction of the sheath from the patient.