Electrode fixation in interventional medical systems

An implantable medical device assembly includes a mounting structure, an electrode, and fixation tines. The electrode protrudes from a surface of the structure, offset proximally from a distal end of the structure, and approximately centered between first and second sides of the structure. Each tine extends away from the surface—a first adjacent the first side, and a second adjacent the second side. Each tine is elastically deformable from a relaxed condition, in which the tine extends toward a proximal end of the structure, to an extended condition, in which the tine extends away from the distal end of the structure. A delivery tool has first and second longitudinally extending sidewalls to receive passage of the structure therebetween. When the structure distal end is located between proximal ends of the sidewalls, a rail-like edge of each sidewall receives, and elastically deforms to the extended condition, a corresponding tine.

CROSS-REFERENCE TO RELATED APPLICATION

The instant application is related to the co-pending and commonly assigned United States patent application entitled, ELECTRODE FIXATION IN INTERVENTIONAL MEDICAL SYSTEMS, having the Ser. No. 15/287,122, which was filed on Oct. 6, 2016, and is hereby incorporated by reference.

TECHNICAL FIELD

The present invention pertains to interventional medical systems, and, more specifically, to implantable electrode fixation at a stimulation site.

BACKGROUND

An implantable medical device, for the delivery of stimulation therapy, may include an electrode and a fixation component configured to hold the electrode in intimate contact with tissue at a stimulation site. One type of such a device may be an implantable cardiac pacemaker that includes a pulse generator and a pacing electrode coupled to the generator, for example, by an elongate insulated lead wire. A pacing site may be located on an epicardial surface of the heart, for example, on the left side of the heart for the application of pacing therapy to treat heart failure.FIG. 1is a schematic showing an access site A for creating a passageway between a patient's diaphragm19and xiphoid process20of sternum13, for example, to implant a pacing electrode on an epicardial surface6of the patient's heart, which is enclosed within the pericardial sac15. After making a superficial incision, an operator may open a passageway between diaphragmatic attachments18and diaphragm19by using blunt dissection tools and techniques that are known in the art. Then, the operator may employ a piercing tool to pass a guide wire through the pericardial sac15, also according to methods known in the art. The operator may use fluoroscopic guidance to position a distal portion of the guide wire along a portion of epicardial surface6, at which a target site is located, and then pass a guiding sheath over the positioned guide wire. The guiding sheath then serves as a conduit for delivery of the implantable electrode to the target site. In this context, to deliver and then fix, or secure the implantable electrode at an epicardial site, there is a need for new configurations of interventional systems and associated implantable device assemblies.

SUMMARY

An implantable medical device assembly, according to some embodiments, includes a mounting structure, an electrode, and first and second tissue-penetrating fixation tines; wherein the electrode protrudes from a surface of the structure at a location that is offset proximally from a distal end of the structure and is approximately centered between first and second sides of the structure, and wherein a segment of each fixation tine extends away from the surface of the structure, the first fixation tine segment, at a location adjacent the first side and distal end of the structure, and the second fixation tine segment, at a location adjacent the second side and distal end of the structure. Each tine segment is elastically deformable from a relaxed condition to an extended condition; wherein, in the relaxed condition, each tine extends toward a proximal end of the mounting structure so that a piercing tip of each tine is located adjacent to the electrode, and, in the extended condition, each tine extends away from the distal end of the mounting structure, so that each piercing tip is located distal to the distal end of the mounting structure.

In some embodiments, each fixation tine is a component formed from a super-elastic wire, and the component may include a mounting segment (e.g., pre-formed in an L-shape), and the above-described segment (e.g., pre-formed in a V-shape), which extends from the surface of the mounting structure and is terminated by the piercing tip. The segments may bend toward one another, in a single plane, the same for both. In the above described assembly, the mounting structure may include first and second channels that extend lengthwise, between the proximal and distal ends of the structure, wherein the mounting segment of each fixation tine extends a corresponding channel.

An interventional medical system, according to some embodiments, includes the above described device assembly and a delivery tool, which has first and second longitudinally extending sidewalls spaced apart from one another to receive passage of the assembly mounting structure therebetween, so that, when the structure is passed therebetween, until the distal end thereof is located between proximal ends of the sidewalls, a rail-like edge of each sidewall receives in engagement therewith, and elastically deforms to the extended condition, a corresponding fixation tine segment. According to some methods, after an operator positions the holding member and the device assembly, with the fixation tines in the extended condition, at an epicardial site, the operator releases the fixation tines from the extended condition, to engage with tissue at the site, by applying a push force to the mounting structure of the device assembly.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives.

FIGS. 2A-Bare plan views, from different perspectives, of an implantable medical device assembly300, according to some embodiments. A mounting structure310of device assembly300is shown having a length defined from a proximal end31P to a distal end31D thereof, a thickness defined from a first surface311to a second surface312thereof, and a width defined from a first side301to a second side302thereof.FIGS. 2A-Billustrate assembly300including an electrode32protruding from first surface311of structure310at a location offset proximally from structure distal end31D and offset from and approximately centered between first and second sides301,302. According to some exemplary embodiments, structure310may be formed from a biocompatible and biostable insulative polymer, such as silicone, or urethane, or a combination thereof.FIGS. 2A-Bfurther illustrate first and second tissue-penetrating fixation tines341,342of assembly300being located on either side of electrode32, wherein first tine341extends from surface311of structure310at a location adjacent to first side301and distal end31D, and second tine342extends from surface311at a location adjacent to second side302and distal end31D. Each tine341,342includes a tissue-piercing tip40, andFIGS. 2A-Bshow tines341,342in a relaxed condition, bending toward proximal end31P and first surface311of structure310, so that each piercing tip40is located adjacent to electrode32. According to preferred embodiments, each tine341,342is formed from a super-elastic material and includes a pre-formed V-shaped segment4V configured to secure electrode32, in intimate tissue contact, at a stimulation site on an epicardial surface of a patient's heart. Electrode32may be constructed from any suitable material and by any suitable method known to those skilled in the art of medical electrical cardiac pacing.

Pre-formed V-shaped segment4V of each fixation tine341,342is elastically deformable from the illustrated relaxed condition, which is that of the pre-formed V-shape, to an extended condition, in which each segment4V extends distally away from distal end31D of structure310, so that tips40are located distal to structure distal end31D, for example, as described below in conjunction withFIG. 4A. Tines341,342may be held in the extended condition until an operator positions assembly300in proximity to a stimulation site, after which the operator may release tines341,342from the extended condition so that piercing tips40‘bite’, or penetrate into tissue adjacent the site, thereby securing electrode32in intimate tissue contact for stimulation therapy.

With reference toFIG. 2A, in conjunction withFIG. 2C, which is another plan view of device assembly300, each tine341,342may be secured to structure310by a pre-formed L-shaped segment4L thereof (dashed lines inFIG. 2A).FIG. 2Cillustrates each L-shaped segment extending in a corresponding channel318of mounting structure, being interlocked therewith, and, for example, further secured thereto by a backfill of a medical grade adhesive material, according to some embodiments. According to the illustrated embodiment, each channel318extends through structure310, from first surface311toward second surface312and then lengthwise adjacent to a corresponding side301,302of structure310. However, according to alternate embodiments, in which the means for mounting tines341,342is varied, what is herein designated as the L-shaped segment4L of the illustrated embodiment can be pre-formed into any other suitable shape that conforms to alternate mounting means.

FIG. 3Ais a plan view of either of tissue-penetrating fixation tines341,342as a separate component from assembly300, according to some embodiments.FIG. 3Aillustrates tine341,342including the aforementioned pre-formed L-shaped and V-shaped segments4L,4V, wherein L-shaped segment4L extends from a first end4L1thereof to a second end4L2thereof around a bend that encloses a 90 degree angle, and V-shaped segment4V extends from second end4L2of L-shaped segment4L to piercing tip40, and bends toward L-shaped segment4L.FIG. 3Afurther illustrates V-shaped segment4V including a first, relatively straight, portion4V-1, a second, arched, portion4V-2, and a third, relatively straight, portion4V-3, wherein second portion4V-2connects first and third portions4V-1,4V-3, and third portion4V-3is terminated by piercing tip40. A length of third portion4V-3, for example, about 0.12 inch, sets a depth to which each tine341,342can penetrate into tissue at an implant site; and a length of second portion4V-2, for example, about 0.08 inch around a radius of about 0.03 inch, adds a bit of depth to the penetration and determines how much tissue is encompassed by the penetrating tines341,342. The release of tines341,342for ‘biting’ is described in greater detail below, in conjunction withFIG. 6.

FIG. 3Bis cross-section view of tine342, through section line B-B ofFIG. 3A, and, with reference toFIG. 3Bin conjunction withFIG. 3A, each tine component341,342has a generally rectangular axial cross-section that is uniform along both segments4L,4V, sans piercing tip40, wherein a single plane in which both segments4L,4V bend is orthogonal to longer sides of the axial cross-section. According to an exemplary embodiment, tine components341,342may be formed from a rolled Nitinol wire (e.g., having a diameter of approximately 0.012 inch, prior to rolling), and piercing tip40is formed by a first angled surface cut in one of the longer sides of the axial cross-section, according to an angle π (FIG. 3A), for example, of about 25 degrees. Each of tine components may also include a second angled surface cut into one of the shorter sides of the axial cross-section, according to an angle β (FIG. 3B), for example, of about 60 degrees, wherein, with further reference toFIG. 3B, in conjunction withFIG. 2B, the second angled surfaces of tines341,342face generally toward one another in assembly300, such that the dashed line inFIG. 3Brepresents the second angled surface of tine341.

With further reference toFIGS. 2A-B, when device assembly300forms an implantable medical electrical lead, assembly300further includes an elongate conductor that is coupled to electrode32(dashed line inFIG. 2B), and an elongate insulation body210that is joined to mounting structure310and extends around the conductor to provide electrical isolation. According to the illustrated embodiment, the conductor extends proximally from proximal end31P of structure310and within insulation body210to a connector subassembly215, which is configured for coupling to an implantable pulse generator, such as a pacemaker (not shown).FIG. 2Bfurther illustrates device assembly including one or more optional additional electrodes35,36and corresponding insulated conductors (dashed lines) coupled thereto. Optional electrode35is shown mounted to surface311of structure310, for example, for bipolar function with electrode32, according to some embodiments; alternately, electrode35can be mounted opposite electrode32, to second surface312of mounting structure310. Optional electrode36is shown mounted to an elongate insulation body610that extends distally from distal end31D of mounting structure310, and through which the corresponding conductor (dashed line) extends. According to an exemplary embodiment that includes electrode36, electrode36may be spaced apart from electrode32by a distance of about one to two inches, for example, to create a ‘wide’ dipole for atrial sensing. A construction of the conductor(s), insulation body210(and optional body610), and connector subassembly215of assembly300, as well as of the pulse generator, may be according to any suitable means known to those skilled in the art of implantable medical stimulation systems.

FIGS. 4A-Bare a plan view and an end view of an interventional medical system, according to some embodiments, that includes a delivery tool500together with device assembly300; andFIG. 4Cis perspective view of a portion of the system, according to some embodiments.FIGS. 4A-Cillustrate device assembly300received between first and second longitudinally extending sidewalls531,532of a holding member530of delivery tool500, which holding member530is attached to a distal end of an elongate shaft510of tool500.FIGS. 4B-Cillustrate sidewalls531,532being spaced apart from one another, to receive passage of device assembly300therebetween, and each sidewall531,532including a rail-like edge531E,532E. With further reference toFIGS. 4A and 4C, each sidewall531,532extends over a length defined from a proximal end531P,532P thereof to a distal end531D,532D thereof, and edges531E,532E extend along the length. According to the illustrated embodiment, each sidewall edge531E,532E is sized to receive in engagement therewith, and to elastically deform, from the relaxed condition to the extended condition, V-shaped segment4V of a corresponding fixation tine341,342, when proximal end31P of device assembly mounting structure310, with surface311facing toward edges531E,532E, is passed between sidewalls531,531(e.g., per arrow L), from distal ends531D,532D thereof to proximal ends531P,532P thereof, and then proximally beyond. (Dashed lines inFIG. 4Adepict distal end31D of mounting structure310between holding member sidewalls351,352, and the extended condition of tines341,342, being engaged in edges351E,352E.) Thus, an operator may employ tool500to position device assembly300, with tines341,342in the extended position, at an epicardial site.

According to some embodiments, holding member530further includes means for engaging device assembly mounting structure310, in proximity to proximal end31P, when distal end31D is located between holding member sidewalls531,532, to prevent distal end31D from passing proximally out from between sidewalls531,532.FIGS. 4A and 4Cillustrate this means being first and second stop members535A,535B that extend proximally from respective sidewall proximal ends531P,532P, and are oriented to abut respective first and second sides301,302of mounting structure310, for example, by extending inward toward one another, as best seen inFIG. 4C. Furthermore, with reference toFIGS. 2B-C, in conjunction withFIG. 4C, mounting structure sides301,302may taper toward one another so that the width of structure310in proximity to proximal end31P is less than the width in proximity to distal end31D.

According to some embodiments, shaft510of tool500is formed by a tubular member, for example, which is attached around a shank533of holding member530, as shown inFIG. 4A.FIG. 4Afurther illustrates insulation body210of device assembly300extending within shaft510of tool500so that connector assembly215extends proximally therefrom. But, in some alternate embodiments, insulation body210may extend alongside delivery tool shaft510.

According to an exemplary embodiment, shaft510of delivery tool500, for example, extending over a length of approximately 30 cm to 35 cm, may be formed by a stainless steel braid-reinforced medical grade polymer of one or more appropriate grades of polyether block amide (e.g., PEBAX® 6333 and 7033); and holding member530of tool500may be formed from an appropriate grade of polyether block amide (e.g., PEBAX® 7233) and include a radiopaque marker bonded thereto, for example, a Platinum/Iridium or gold marker, or a polyamide material with a radiopaque filler, such as Tungsten-filled Vestamid®.

FIG. 5is a schematic showing holding member530of delivery tool500having been positioned in the pericardial space, via sub-xiphoid access, so the operator can secure electrode32of device assembly300at the epicardial site, for example, to provide pacing stimulation.FIG. 5illustrates a guiding sheath700providing a passageway for the insertion of delivery tool500into the pericardial space, between epicardial surface6and pericardial sac15, through access site A, which may be formed by any suitable method known in the art, for example, as described above in conjunction withFIG. 1. Fluoroscopic or video monitoring may be employed for guidance in positioning holding member530. Alternately, the operator may gain access to the pericardial space, to position holding member530and assembly300, via a thoracotomy by methods known in the art. According to some methods, after positioning holding member530and device assembly300at the epicardial site, the operator applies a push force to mounting structure310through an elongate stiffener24that extends in sliding engagement within insulation body210of device assembly300, per arrow P, thereby moving device assembly300distally relative to delivery tool holding member530and releasing fixation tines341,342to penetrate into tissue at the epicardial site. Then, the operator can retract tool500from the pericardial space and withdraw stiffener24from device assembly300. According to some alternate embodiments and methods, and with reference back toFIG. 4A, the operator can apply the push force to mounting structure310through an optional ejector rod54of the interventional medical system, which extends in sliding engagement within tool shaft510.

FIG. 6is a schematic depicting the release of fixation tines341, according to some embodiments. InFIG. 6, positions of tines341,342, which are illustrated with dashed-line representations, correspond to a trajectory of tine release, per arrow R, for penetration of tine piercing tips40into tissue. The solid line representation of tines341,342generally corresponds to full engagement thereof with tissue, which secures electrode32to the epicardial stimulation site. An approximate penetration depth BD of tines341,342may be about 0.132 inch (3.3 mm), as dictated by the above disclosed exemplary radius and lengths of tine portions4V-2and4V-3(FIG. 3A).

In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims.