Active fixation implantable lead with rotation stop features

An implantable medical electrical lead includes an extendable/retractable active fixation distal tip assembly. The distal tip assembly includes a shell having an internal cavity and a helix guide member extending at least partially across the cavity and including an axial surface. The distal tip assembly also includes a rotatable coupler within the cavity and a fixation helix fixedly attached to the coupler. The fixation helix engages the helix guide member such that rotation of the coupler and the fixation helix causes the coupler and the fixation helix to advance distally relative to the shell. The coupler further includes a distal rotation stop member protruding axially from the coupler configured to abut the axial surface of the helix guide member to delimit rotation and extension of the coupler and the fixation helix.

TECHNICAL HELD

The present invention relates to implantable medical devices and relates more particularly to leads for cardiac rhythm management (CRM) systems.

BACKGROUND

Various types of medical electrical leads for use in cardiac rhythm management (CRM) and neurostimulation systems are known. For CRM systems, such leads are typically extended intravascularly to an implantation location within or on a patient's heart, and thereafter coupled to a pulse generator or other implantable device for sensing cardiac electrical activity, delivering therapeutic stimuli, and the like. The leads frequently include features to facilitate securing the lead to heart tissue to maintain the lead at its desired implantation site. Exemplary leads can include a helical fixation member that can be extended from the distal end of the lead and screwed into the cardiac tissue to fixate the lead in place.

SUMMARY

In Example 1, the present invention is an implantable medical electrical lead comprising a flexible insulative body, a connector, a first conductor, a first electrode, and a distal tip assembly. The flexible insulative body has a proximal end and an opposite distal end, and defines a longitudinal axis of the lead. The connector is coupled to the proximal end of the lead body and is configured for operatively coupling the lead to an implantable pulse generator. The first conductor extends within the lead body from the connector toward the distal end of the lead body, and the first electrode is coupled to the body and to the first conductor. The distal tip assembly is coupled to the distal end of the lead body and includes a shell, a coupler and a fixation helix. The shell has an outer wall defining a shell proximal end, an opposite shell distal end, and an internal cavity between the shell proximal and distal ends. The shell further includes a helix guide member extending at least partially across the cavity at or near the shell distal end and defining an axial surface and a distal opening. The coupler is rotatably disposed within the cavity and includes a proximal shaft portion and a distal shaft portion having a distal end, and further includes a distal rotation stop member protruding axially from the distal end of the distal shaft portion. The fixation helix is fixedly coupled to the distal shaft portion of the coupler and includes a distal portion extending at least partially through the distal opening of the shell. The fixation helix and the helix guide member are configured so that the fixation helix slidably contacts a portion of the helix guide member such that rotation of the coupler and the fixation helix causes axial translation of the coupler and the fixation helix relative to the shell between fully retracted and fully extended positions. The distal rotation stop member is configured to abut the axial surface of the helix guide member in the fully extended position so as to delimit further rotation and axial extension of the coupler and the fixation helix.

In Example 2, the implantable medical electrical lead of Example 1, further comprising a second conductor extending within the lead body and connected to the proximal shaft portion of the coupler, wherein the coupler and the fixation helix are electrically conductive and the fixation helix is operable as a second electrode.

In Example 3, the implantable medical electrical lead of either of Examples 1 or 2, wherein the cavity has a generally circular cross-sectional shape and the helix guide member has a generally semi-circular cross-sectional shape when viewed along the longitudinal axis of the lead, such that the distal opening has a generally semi-circular shape.

In Example 4, the medical electrical lead of Example 3, wherein the axial surface of the helix guide member includes a radiused region near an intersection of the axial surface of the helix guide member and an inner surface of the shell outer wall.

In Example 5, the medical electrical lead of any of Examples 1-4, wherein the distal end of the distal shaft portion of the coupler includes a distal radial face, and wherein the distal rotation stop member is disposed radially inward of the fixation helix and protrudes axially from the distal radial face.

In Example 6, the medical electrical lead of any of Examples 1-5, wherein the helix guide member extends radially inward of the outer wall of the shell.

In Example 7, the medical electrical lead of Example 6, wherein the helix guide member does not extend radially inward to the longitudinal axis.

In Example 8, the medical electrical lead of any of Examples 1-7, wherein the distal rotation stop member includes a pair of converging axial surfaces, and wherein one of the converging axial surfaces is configured to abut the axial surface of the helix guide member to delimit further rotation and extension of the coupler and the fixation helix.

In Example 9, the present invention is an implantable medical electrical lead comprising a flexible insulative body, a connector, a first conductor, and a distal tip assembly. The flexible insulative body has a proximal end and an opposite distal end, and defines a longitudinal axis of the lead. The connector is coupled to the proximal end of the lead body and is configured for operatively coupling the lead to an implantable pulse generator. The connector includes a rotatable terminal pin. The first conductor extends within the lead body from the connector toward the distal end of the lead body, and is fixedly coupled to the terminal pin and rotatable within the lead body. The distal tip assembly is coupled to the distal end of the lead body and includes a shell, a coupler, and a fixation helix. The shell has an outer wall defining a shell proximal end, an opposite shell distal end, and an internal cavity between the shell proximal and distal ends. The shell further includes a helix guide member extending across the cavity at or near the shell distal end and defining an axial surface and a distal opening. The coupler is rotatably disposed within the cavity and includes a proximal shaft portion connected to the first conductor such that rotation of the terminal pin causes rotation of the coupler, and a distal shaft portion having a distal end. The coupler further includes a distal rotation stop member protruding axially from the distal end of the distal shaft portion. The fixation helix fixedly is coupled to the distal shaft portion of the coupler and includes a distal portion extending at least partially through the distal opening of the shell. The fixation helix and the helix guide member are configured so that the fixation helix slidably contacts a portion of the helix guide member such that rotation of coupler and the fixation helix causes axial translation of the coupler and the fixation helix relative to the shell between fully retracted and fully extended positions. The distal rotation stop member is configured to abut the axial surface of the helix guide member in the fully extended position so as to delimit further rotation and axial extension of the coupler and the fixation helix.

In Example 10, the implantable medical electrical lead of Example 9, wherein the cavity has a generally circular cross-sectional shape and the helix guide member has a generally semi-circular cross-sectional shape when viewed along the longitudinal axis of the lead, such that the distal opening has a generally semi-circular shape.

In Example 11, the medical electrical lead of either of Examples 9 or 10, wherein the axial surface of the helix guide member includes a radiused region near an intersection of the axial surface of the helix guide member and an inner surface of the shell outer wall.

In Example 12, the medical electrical lead of any of Examples 9-11, wherein the distal end of the distal shaft portion of the coupler includes a distal radial face, and wherein the distal rotation stop member is disposed radially inward of the fixation helix and protrudes axially from the distal radial face.

In Example 13, the medical electrical lead of any of Examples 9-12, wherein the helix guide member extends radially inward of the outer wall of the shell.

In Example 14, the medical electrical lead of Example 13, wherein the helix guide member does not extend radially inward to the longitudinal axis.

In Example 15, the medical electrical lead of any of Examples 9-14, wherein the distal rotation stop member includes a pair of converging axial surfaces, and wherein one of the converging axial surfaces is configured to abut the axial surface of the helix guide member to delimit further rotation and extension of the coupler and the fixation helix.

In Example 16, the present invention is an implantable medical electrical lead comprising a flexible insulative body, a connector, a torque transmission member, and a distal tip assembly. The flexible insulative body has a proximal end and an opposite distal end, and defines a longitudinal axis of the lead. The connector is coupled to the proximal end of the lead body and is configured for operatively coupling the lead to an implantable pulse generator. The torque transmission member extends within the lead body and is accessible from the connector. The distal tip assembly is coupled to the distal end of the lead body and includes a shell, a coupler, and a fixation helix. The shell has an outer wall defining a shell proximal end, an opposite shell distal end, and an internal cavity between the shell proximal and distal ends. The shell further includes a helix guide member extending across the cavity at or near the shell distal end and defining an axial surface and a distal opening. The coupler is rotatably disposed within the cavity and includes a proximal shaft portion mechanically coupled to the torque transmission member, and a distal shaft portion having a distal end. The coupler further includes a distal rotation stop member protruding axially from the distal end of the distal shaft portion, wherein rotation of the torque transmission member causes rotation of the coupler. The fixation helix is fixedly coupled to the distal shaft portion of the coupler and includes a distal portion extending at least partially through the distal opening of the shell. The fixation helix and the helix guide member are configured so that the fixation helix slidably contacts a portion of the helix guide member such that rotation of the torque transmission member, the coupler and the fixation helix causes axial translation of the coupler and the fixation helix relative to the shell between fully retracted and fully extended positions. The distal rotation stop member is configured to abut the axial surface of the helix guide member in the fully extended position so as to delimit further rotation and axial extension of the coupler and the fixation helix.

In Example 17, the implantable medical electrical lead of Example 16, wherein the cavity has a generally circular cross-sectional shape and the helix guide member has a generally semi-circular cross-sectional shape when viewed along the longitudinal axis of the lead, such that the distal opening has a generally semi-circular shape.

In Example 18, the medical electrical lead of either of Examples 16 or 17, wherein the distal end of the distal shaft portion of the coupler includes a distal radial face, and wherein the distal rotation stop member is disposed radially inward of the fixation helix and protrudes axially from the distal radial face.

In Example 19, the medical electrical lead of any of Examples 16-18, wherein the helix guide member extends radially inward of the outer wall of the shell.

In Example 20, the medical electrical lead of any of Examples 16-19 wherein the distal rotation stop member includes a pair of converging axial surfaces, and wherein one of the converging axial surfaces is configured to abut the axial surface of the helix guide member to delimit further rotation and extension of the coupler and the fixation helix.

While multiple embodiments are disclosed, still other embodiments will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.

DETAILED DESCRIPTION

FIG. 1is a schematic view of a cardiac rhythm management (CRM) system10according to one embodiment. As shown inFIG. 1, the CRM system10includes a pulse generator12coupled to a plurality of leads14,16deployed in a patient's heart18. As further shown inFIG. 1, the heart18includes a right atrium24and a right ventricle26separated by a tricuspid valve28. During normal operation of the heart18, deoxygenated blood is fed into the right atrium24through the superior vena cava30and the inferior vena cava32. As further shown, the heart18includes a left atrium33, which receives oxygenated blood from the lungs, and a left ventricle34, which pumps the oxygenated blood to the body.

The leads14,16operate to convey electrical signals and stimuli between the heart18and the pulse generator12. In the illustrated embodiment, the lead14is implanted in the right ventricle26, and the lead16is implanted in the right atrium24. In other embodiments, the CRM system10may include additional leads, e.g., a lead extending into a coronary vein for stimulating the left ventricle in a bi-ventricular pacing or cardiac resynchronization therapy (CRT) system. As shown, the leads14,16enter the superior vena cava30, and are implanted in the right ventricle26and right atrium24, respectively.

The pulse generator12is typically implanted subcutaneously within an implantation location or pocket in the patient's chest or abdomen. The pulse generator12may be any implantable medical device known in the art, or later developed, for delivering an electrical therapeutic stimulus to the patient. In various embodiments, the pulse generator12is a pacemaker, a CRT device, an implantable cardiac defibrillator, and/or includes both pacing, CRT and/or defibrillation capabilities (e.g., a CRT-D device).

As explained in greater detail herein, the leads14,16are actively fixated to the cardiac tissue by a fixation helix that is configured to be screwed into the cardiac tissue. In the various embodiments, the fixation helix is a so-called “extendable/retractable” type in that it can be substantially or entirely retracted within the lead structure, e.g., during advancement of the lead14or16to the desired implantation site, and thereafter extended distally to expose a portion of the fixation helix so that it can be screwed into the endocardium. In some embodiments, the fixation helix is electrically active and thus can be used to sense the electrical activity of the heart18or to apply a stimulating pulse to the cardiac tissue. In other embodiments, the fixation helix is not electrically active and merely operates as a fixation means.

FIG. 2Ais an elevation view of the lead14in a non-implanted state. As shown inFIG. 2A, the lead14is defined by a proximal region60and a distal region64. Generally speaking, the proximal region60is dimensioned so as to make up the portion of the lead14extending from the pulse generator12to the location at which the lead14enters the right atrium24via the superior vena cava30, whereas the distal region64is dimensioned to extend within the heart18to the location at which the lead14is attached to the endocardium (seeFIG. 1).

In the embodiment illustrated inFIG. 2A, the lead14includes a flexible body68, a proximal connector72, a distal tip assembly75, and a suture sleeve76. As shown, the body68includes a proximal end80and an opposite distal end82. The proximal connector72is coupled to the proximal end80of the body68, and the distal tip assembly75is coupled to the distal end82of the body68. In the illustrated embodiment, the lead14includes a polymer boot69covering the proximal end80of the body68as well as a portion of the connector72. Additionally, the elongate body68defines, in the illustrated embodiment, a longitudinal axis83of the lead14. The boot69operates, when present, to reinforce the transition between the lead body68and the connector72as well as to provide a seal between the connector72and the header on the pulse generator12(seeFIG. 1) to which the lead14is connected. The suture sleeve76provides a structure to support the lead14so that it can be sutured to fascia or muscular tissue to inhibit movement of the lead14after implantation. The operation of the boot69and the suture sleeve76is not critical to the various embodiments disclosed herein, and thus are not described in further detail.

FIG. 2Bis an elevation view of the lead16in a non-implanted state. As can be seen inFIG. 2B, the lead16is in many respects similar or identical to the lead14, and has a proximal region84and a distal region88. Additionally, the lead16includes a flexible, elongate body90, a proximal connector92, a distal tip assembly94and a suture sleeve95. As shown, the body90has a proximal end96and a distal end97opposite the proximal end96. The proximal connector92is coupled to the proximal end96of the body90, and the distal tip assembly94is coupled to the distal end97of the body90, as in the lead14. Similar to the lead14, the lead body90defines a longitudinal axis98of the lead16. Additionally, the lead16includes a polymer boot101covering the proximal end96of the body90as well as a portion of the connector92. As can be seen inFIG. 2B, the lead16primarily differs structurally from the lead14in that the distal region88of the lead16includes a pre-formed curved portion99shaped into a J-shape to direct the tip assembly94toward the desired attachment location within the right atrium24. The leads14,16are otherwise generally identical, and so for expediency, various embodiments of the lead14will be described herein, although it is emphasized that the described features and functionality can be readily applied to a right atrial lead such as the lead16.

FIGS. 3A and 3Bare partial cross-sectional views of the lead14according to an exemplary embodiment. As shown inFIGS. 3A and 3B, the lead14includes, in the illustrated exemplary embodiment, an inner coil conductor100, an outer coil conductor104, and a ring electrode assembly108. Additionally, the connector72includes a terminal pin110, a ring contact114and a seal member116. In the illustrated embodiment, the connector72is a conventional bi-polar connector, e.g., an IS-1 connector, configured to mechanically and electrically couple the lead14to a header of the pulse generator12(seeFIG. 1). As such, the ring contact114and the terminal pin110are each electrically conductive and electrically isolated from one another, and are adapted to engage a corresponding contact within the pulse generator header. In one embodiment, as discussed in further detail herein, the terminal pin110is rotatable relative to the ring contact114and the lead body68, and is operable to facilitate extension and retraction of a fixation helix/electrode housed within the distal tip assembly75. However, other embodiments may utilize other connector72configurations, depending on the configuration of the corresponding pulse generator12.

As further shown, in the illustrated embodiment, the distal tip assembly75includes a shell120, a coupler124, a fixation helix130, a weld sleeve134, a rear plate138, a seal member140and a drug collar141. As illustrated, the shell120includes an outer wall144extending from a proximal end148to a distal end152and enclosing an internal cavity156, and has a longitudinal axis158generally corresponding to the longitudinal axis83of the lead14. Additionally, the shell120includes a helix guide member160extending across the cavity156. The helix guide member160includes an axial surface164and defines a distal opening168into the cavity156.

In the illustrated embodiment, the coupler124operates as a rotatable shaft, and thus is rotatably disposed within the cavity156and includes a proximal shaft portion172and a distal shaft portion176including a distal end178. As further shown, the coupler124includes a distal rotation stop member182protruding axially from the distal end178of the coupler distal shaft portion176.

In the embodiment ofFIGS. 3A and 3B, the fixation helix130has a proximal portion184and a distal portion188terminating in a sharpened distal tip190. As shown, the proximal portion184of the fixation helix130is coupled to the distal shaft portion176of the coupler124. The fixation helix130can be fixedly attached to the distal shaft portion176by any mechanical attachment means or technique, e.g., welding, brazing, crimping, and the like. In one embodiment, as shown, the attachment strength of the fixation helix130to the distal shaft portion176is enhanced by virtue of threads formed onto the distal shaft portion176, although this is not a requirement. In the illustrated embodiment, both the coupler124and the fixation helix130are made of an electrically conductive material.

The lead body68is in the form of a flexible, elongate tube of electrically insulative material, and the inner and outer coil conductors100,104extend longitudinally within the lead body68. In the illustrated embodiment, the coil conductors100,104are configured in a coaxial, non-coradial configuration as is known in the art. Additionally, a tubular inner insulating sheath192is disposed between the inner and outer conductor coils100,104. However, in various embodiments, e.g., those in which the inner and outer coil conductors100,104are separately insulated, the inner insulating sheath192may be omitted. In the illustrated embodiment, the lead body68is a multi-part structure and includes a distal segment193between the ring electrode assembly108and the distal tip assembly75. However, in other embodiments, the lead body69may be a single, unitary tubular element. In short, the specific configuration of the lead body68is not of particular importance to the various embodiments, and so any number of lead body designs can be utilized.

In addition, although not visible inFIG. 3Aor3B, the inner and outer coil conductors100,104are both mechanically and electrically connected to the terminal pin110and the ring contact114, respectively, within the connector72. Thus, because as explained elsewhere the terminal pin110is rotatable relative to the lead body68, the inner conductor100is also rotatable within the lead body68and can operate as a torque transmission member to transmit torque applied to the terminal pin110. In addition, the coiled configuration of the inner coil conductor104defines an inner lumen for receiving a stylet or similar instrument to facilitate delivery of the lead14.

As illustrated, the outer coil conductor104is both mechanically and electrically connected to the ring electrode assembly108, which operates as a low-voltage pace/sense electrode as is known. The specific design and construction of the ring electrode assembly108and/or the connection of the outer coil conductor104thereto are of no particular importance to the various embodiments. Thus any electrode or conductor design, whether now known or later developed, may be used in lieu of or in addition to the outer coil conductor104and/or the ring electrode assembly108.

As also illustrated, the inner coil conductor100is fixedly coupled, both mechanically and electrically, to the proximal shaft portion172of the coupler. Thus, because both the coupler124and the fixation helix130are electrically conductive, the inner coil conductor100is configured to transmit electrical signals and/or stimuli between the terminal pin110and the fixation helix130, which operates as a low voltage pace/sense electrode. Consequently, in the illustrated embodiment, the ring electrode assembly108and the fixation helix130combine to provide bi-polar pacing and sensing capabilities.

As previously explained, in the illustrated embodiment, the inner coil conductor100operates as a torque transmission member, such that rotation of the terminal pin110relative to the body68causes rotation of the coupler124and the fixation helix130relative to the shell120. In turn, the fixation helix130is arranged within the shell120such that a surface of the fixation helix130contacts and slidably engages the helix guide member160. This engagement of the fixation helix130and the helix guide member160thus causes the fixation helix130(and consequently, the coupler124) to translate axially relative to the shell120as the fixation helix130rotates relative to the shell120. Thus, in the various embodiments, the interaction of the fixation helix130and the helix guide member160effectuates the desired extension and retraction of the fixation helix130as the terminal pin110is rotated by the implanting physician. In this respect, the fixation helix130and helix guide member160operate in substantially the same manner as the fixation helix and the guide elements disclosed in co-pending and commonly assigned U.S. application Ser. No. 12/785,941, the contents of which are incorporated herein by reference.

In various embodiments, the seal member140operates to substantially prevent ingress of bodily fluids into the internal region of the lead14, and in the illustrated embodiment is capable of translating axially within the shell120along with the coupler124. In one embodiment, the seal member140can be configured to be substantially the same as or identical to any of the shaft seals disclosed in co-pending and commonly assigned U.S. application Ser. No. 12/818,691, the contents of which are incorporated herein by reference. In other embodiments, however, other seal configurations are employed, or alternatively, a shaft seal can be omitted altogether. Additionally, the drug collar141can be any drug eluting element such as are known in the art.

As shown, the distal rotation stop member182is positioned radially inward of the fixation helix130. In various embodiments, the distal rotation stop182is sized and shaped so as to abut the axial surface164of the helix guide member160upon a pre-determined amount of extension of the coupler124relative to the shell120. That is, the coupler124and the fixation helix130can be advanced distally (again, by rotation of the terminal pin110relative to the lead body68) until the distal rotation stop182abuts the axial surface164, at which point further rotation of the coupler124in the extension direction is prevented. Accordingly, the interaction of the distal rotation stop182and the axial surface164operates to delimit rotation, and consequently, axial extension of the coupler124and the fixation helix130beyond a predetermined limit. This will advantageously prevent over-rotation of the coupler124and the fixation helix130, and thus will tend to maintain desired radial alignment of the fixation helix130relative to the shell120. If this radial alignment is not maintained, the potential could exist for the fixation helix130to wedge against the helix guide member160. The operation of the distal rotation stop182and the axial surface164thus promotes smooth operation of the fixation helix130, in particular, smooth retraction of the fixation helix130after it has been fully extended.

In addition, in various embodiments, the weld sleeve134and the rear plate138may include mating teeth or similar projections that interact to delimit further rotation of the coupler124once the coupler124and the fixation helix130are fully retracted within the shell120.

In various embodiments, it may be desirable to maintain part of the distal portion188of the fixation helix130extending distally beyond the helix guide member160even when the fixation helix130is fully retracted. This ensures that the fixation helix130will engage the helix guide member160to allow for extension of the fixation helix130, and also advantageously enables the physician to use the electrically active fixation helix130to map cardiac tissue and thereby identify an optimal attachment site. In the illustrated embodiment, helix guide member160is recessed a nominal amount from the distal end152of the shell124. Recessing the helix guide member160in this manner allows the distal tip190of the fixation helix130to extend distally beyond the helix guide member160for the aforementioned reasons, while at the same time utilizes the portion of the shell120extending beyond the helix guide member160to at least partially shield the exposed portion of the fixation helix130from body tissue. This configuration advantageously inhibits unintended interaction between the fixation helix130and the vascular or cardiac tissue, e.g., during delivery and deployment of the lead14.

FIG. 4is a partial cross-sectional view of the portion of the lead14shown inFIG. 33but with the fixation helix130in its fully extended state. As shown inFIG. 4, the coupler124of the distal tip assembly75is advanced distally within the shell120(as compared to its substantially fully retracted state shown inFIGS. 3A&B). In this position, the distal rotation stop182abuts the axial surface164of the helix guide member160so as to prevent further rotation and axial extension of the coupler124. At the same time, however, the engagement of the distal rotation stop182and the axial surface164provides little to no resistance to reverse rotation and retraction of the coupler124.

FIGS. 5A-5Bare perspective and distal end elevation views of the shell120according to one embodiment. As shown inFIGS. 5A-5B, the shell120and the cavity156have a generally circular cross-sectional shape, and the helix guide member160has a generally semi-circular shape, e.g., a D-shape. In the illustrated embodiment, the axial surface164of the helix guide member160includes a radiused region194near the intersection of the axial surface164and an inner surface195of the shell outer wall144. The radiused region194can generally facilitate ease of manufacturing of the shell120by accommodating tooling used to form the shell120. Of course, in other embodiments, the radiused region194can be omitted.

In general, the configuration of the helix guide member160determines the size and shape of the distal opening168at or near the distal end152of the shell120. Accordingly, in the illustrated embodiment, the distal opening168also has a generally semi-circular shape. The presence of the distal opening168can, in various embodiments, allow ingress of blood and tissue into the cavity156, which can improve the strength of the attachment of the lead14to the heart18. In various embodiments, the size and shape of the helix guide member160can be tailored to provide optimal performance of the distal tip assembly75, and at the same time provide a desired amount of tissue ingrowth into the cavity156.

In the illustrated embodiment, the helix guide member160is sized and positioned so that the axial surface164extends through the longitudinal axis158of the shell120, and consequently, also extends through the longitudinal axis83of the lead14(seeFIG. 3B). Thus, the helix guide member160and the distal opening168have the same general size and shape, and will substantially mirror each other (when viewed along the longitudinal axes83,158). In other embodiments, the helix guide member160has a semi-circular D-shape similar to the embodiment shown inFIGS. 5A-5B, but the axial surface164is radially offset from the longitudinal axis158of the shell120and the longitudinal axis83of the lead14. Consequently, in such embodiments, the distal opening168has a larger cross-sectional area than the helix guide member160when viewed along the axes83,158.

FIGS. 6A-6Bare perspective and distal end elevation views of the coupler124according to one embodiment. As shown inFIGS. 6A-6B, the coupler124has a distal radial face196at the distal end178of the distal shaft portion176, and the distal rotation stop member182protrudes axially from this distal radial face196. As further shown, the distal rotation stop member182generally has a shape of a partial pie piece with its “tip” omitted. As such, the distal rotation stop member182includes a pair of converging axial surfaces197,198, with the axial surface197configured to abut the axial surface164of the helix guide member160to delimit rotation and extension of the coupler124and the fixation helix130as described elsewhere. The shape of the distal rotation stop member182illustrated inFIGS. 6A-6B, i.e. can promote smooth operation of the distal tip assembly75(FIG. 2A) by promoting pure rotational movement of the coupler124in the retraction direction. That is, omission of the “tip” of the pie piece-shaped distal rotation stop member182can eliminate the likelihood that the distal rotation stop member182will pivot about the point of the “tip” (if present). Such pivoting movement would tend to urge the coupler124radially thereby tending to resist rotation of the coupler124.

In various other embodiments, the distal rotation stop182can take on other cross-sectional shapes. For example, in one embodiment, the distal rotation stop member182has a pie piece shape. In one embodiment, the distal rotation stop member182has a generally circular cross-sectional shape. In still other embodiments, the distal rotation stop member182can have other cross-sectional shapes, e.g., rectangular, elliptical, etc.

The various components of the lead14can be made from any known or later developed lead construction materials. For example, the lead body68can be made from any flexible, electrically insulative material suitable for human implantation. Exemplary materials for use as the body68can include polyurethane, silicone rubber, and co-polymers of both, and can include surface or other treatments (e.g., plasma treatments, lubricious coatings, and the like) based on the functional requirements of the lead14. The coil conductors100,104can also be made of any known or later developed lead conductor materials.

Similarly, the components of the distal tip assembly75can be any known or later developed materials. In various embodiments, the shell120is made of a non-electrically conductive material such as polyether sulfone (PES), polyurethane-based thermoplastics, ceramics, polypropylene and polyetheretherketone (sold under the brand name PEEK™). Additionally, the coupler124and the fixation helix130can be made of any known or later developed conductive material, typically a metal such as Elgiloy, MP35N, tungsten, tantalum, iridium, platinum, titanium, palladium, stainless steel as well as alloys of any of these materials. In various embodiments, the fixation helix130can include a surface treatment or coating, such as a coating of iridium oxide, to enhance the electrical performance of the helix130. Alternatively, the coupler124and/or the fixation helix130can be made of non-electrically conductive materials such as any of the materials described previously with respect to the shell120. Similarly, in various embodiments utilizing a conductive shell120, the shell can be made of any of the materials described with respect to the coupler124and the fixation helix130.

In various embodiments, the helix guide member160can have a shape other than the semi-circular D-shape of the embodiment ofFIGS. 5A-5B. For example,FIGS. 7A-7Bare perspective and distal end elevation views of an alternative shell320for use in a lead distal tip assembly according to another embodiment. As shown inFIGS. 7A-7B, the shell320is in most respects similar or identical to the shell120, and includes an outer wall344extending from a proximal end348to a distal end352and enclosing an internal cavity356, and has a longitudinal axis358generally corresponding to the longitudinal axis83of the lead14(seeFIG. 2A). Additionally, the shell320includes a helix guide member360in the form of a radial projection extending radially inward of the outer wall344of the shell320. In this embodiment, the helix guide member360thus has an axial surface364dimensioned and positioned so that it will be engaged by the distal rotation stop member182of the coupler124as described herein to delimit further rotation and extension of the coupler124and the fixation helix130(seeFIGS. 3B & 4). In the illustrated embodiment, the helix guide member360does not extend radially inward to the longitudinal axis358or the longitudinal axis83of the lead14. In various other embodiments, the helix guide member360can extend to or beyond the longitudinal axes83,358. The configuration of the helix guide member360thus provides for a relatively large distal opening368(as compared to other embodiments described herein).

FIGS. 8A-8Bare perspective and distal end elevation views of another alternative shell420for use in a lead distal tip assembly according to yet another embodiment. As shown inFIGS. 8A-8B, the shell420is in most respects similar or identical to shells120and320(FIGS. 5A and 7A, respectively), and includes an outer wall444extending from a proximal end448to a distal end452and enclosing an internal cavity456, and has a longitudinal axis458generally corresponding to the longitudinal axis83of the lead14(seeFIG. 2A). Additionally, the shell420includes a helix guide member460in the form of a radial projection extending radially inward of the outer wall444of the shell320along with portions that extend along the outer wall444. In this embodiment, the helix guide member460thus has an axial surface464dimensioned and positioned so that it will be engaged by the distal rotation stop member182of the coupler124as described herein to delimit further rotation and extension of the coupler124and the fixation helix130(seeFIGS. 3B & 4). In the illustrated embodiment, the helix guide member460does not extend radially inward to the longitudinal axis458or the longitudinal axis83of the lead14. In various other embodiments, the helix guide member460can extend to or beyond the longitudinal axes83,458. The configuration of the helix guide member460thus provides for a relatively large distal opening468(as compared to some other embodiments described herein), similar to the opening368inFIGS. 7A-7B. The shape and size of helix guide member460is yet another example of such a feature that may be included in the claimed implantable medical electrical lead. However, other sizes and shapes are also contemplated.

While the embodiments described herein have been primarily in connection with the lead14, it is emphasized that the distal tip assembly75is also advantageously utilized in the J-shaped atrial lead16. In various embodiments, the J-shape of the lead16results in relatively high torque requirements to rotate the fixation helix130due to the need for the torque transmission element (i.e., the inner coil conductor100) to traverse and rotate through the J-shaped region of the lead16. Such torque requirements would otherwise create the potential for over extension and wedging of the fixation helix of the lead16against the helix guide member, which is substantially prevented by the inclusion of the distal rotation stop member and the interaction of the distal rotation stop member with the axial surface of the helix guide member as described with respect to the lead14.

Additionally, while the lead14has been described herein as having an electrically active fixation helix130operating as a pace/sense tip electrode, in other embodiments, the fixation helix130can be electrically inactive and thus operate solely as a fixation element. In such embodiments, for example, the lead14may be a unipolar lead. In other embodiments, the lead14may include a second ring electrode in addition to the ring electrode assembly108. For example, in one embodiment, the shell120(or the shell220,320or420) can be made from an electrically conductive material and can be electrically and mechanically coupled to the inner coil conductor100or a different coil or cable conductor. Any number of different conductor and/or electrode configurations are contemplated within the scope of the disclosed embodiments.

Furthermore, while the lead14utilizes the terminal pin110and the inner coil conductor100as torque transmission means, in other embodiments, a stylet or similar instrument may be used to rotate the coupler124to actuate the fixation helix130. In still another embodiment, the coupler124may be coupled to a torque transmission member (e.g., a metallic or polymeric coil) extending within the lead body68and coupled to the rotatable terminal pin110but which may be electrically non-conductive. In such embodiments, the terminal pin110may still be utilized to rotate and extend/retract the fixation helix130, but the fixation helix130need not be electrically active.