Implantable medical electrical lead construction and associated implant systems

A temporary medical electrical lead includes a connector pin and a single conductor coil. The coil being close-wound and having no turns of the coil distal portion being mechanically coupled together. The coil distal portion translates a force of no greater than 0.1 lbf (0.4 N) when strained 400%.

FIELD

The present disclosure pertains to medical electrical stimulation, and more particularly to constructions of, and systems including implantable medical electrical leads suitable for selective nerve stimulation, for example, stimulation of the sacral nerves.

BACKGROUND

Neurostimulation, via a medical electrical lead that is implanted with at least one stimulation electrode positioned on or near the sacral nerves, can provide control over urinary incontinence or other pelvic floor disorders. Typically, this stimulation is initially evaluated with what is known as a trialing, or temporary lead that is implanted for a relatively short period of time, for example, seven to thirty days, in order to determine if and how a patient will respond to such stimulation.FIG. 1is a schematic showing such a temporary medical electrical lead200percutaneously implanted for stimulation of a patient's sacral nerves, wherein lead200extends through an incision6at a dorsal surface5of the patient's body3and through one of a series of holes or foramina4of a patient's sacrum2.

SUMMARY

The present disclosure relates to constructions of, and systems including implantable medical electrical leads suitable for selective nerve stimulation, for example, stimulation of the sacral nerves. The implantable medical electrical leads may be temporary medical electrical leads that form a single conductor coil. The single conductor coil may be strained at least 300% or 400% and may not transmit a force greater than 0.1 lbf(0.4 N).

In one aspect, a temporary medical electrical lead includes a connector pin and a single conductor coil. The coil extending from a proximal portion to a distal portion and having a length. The coil being close-wound along the length. The proximal portion of the coil is coupled to the connector pin and a distal portion of the coil extends to a distal-most tip of the lead. The distal portion of the coil defines an inner surface of the lead. The inner surface surrounding an elongate lumen of the lead. The connector pin includes an elongate bore that defines a proximal-most portion of the elongate lumen and a proximal opening thereto at a proximal end of the connector pin. No turns of the coil distal portion are mechanically coupled together. The coil distal portion translates a force of no greater than 0.1 lbf(0.4 N) when strained 400%.

In another aspect, a system for providing temporary medical electrical stimulation includes the temporary medical electrical lead described herein, an introducer needle, a stylet, and a grip tool. The introducer needle has a lumen sized to receive passage of an entire length of the lead therethrough, from a proximal opening of the needle lumen to a distal opening of the needle lumen. The entire length of the lead is defined from the proximal end of the connector pin to the distal-most tip of the lead. The stylet includes a proximal length and a distal length. The distal length has an outer diameter sized to fit in sliding engagement within the elongate lumen of the lead. The proximal length has an outer diameter sized to abut the proximal end of the connector pin of the lead, when the distal length is fitted within the lead lumen. The grip tool is configured to engage with the lead and the stylet to temporarily secure the stylet to the lead when the distal length of the stylet is fitted within the elongate lumen of the lead, and when the proximal length of the stylet abuts the connector pin of the lead.

In another aspect, a method for assembling a system includes, the temporary medical electrical stimulation includes the temporary medical electrical lead described herein, and a stylet. The stylet is configured to fit in sliding engagement within the elongate lumen of the lead. The method includes inserting a distal length of the stylet into the elongate lumen of the lead from the proximal opening thereof, until the distal length of the stylet abuts the distal-most tip of the lead; and securing the lead to the inserted stylet. The securing includes fitting a distal portion of a grip tool around the lead connector pin and a proximal portion of the grip tool around a proximal length of the inserted stylet, so that the proximal end of the connector pin abuts the proximal length of the inserted stylet.

The above summary is not intended to describe each embodiment or every implementation of the present disclosure. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings. In other words, these and various other features and advantages will be apparent from a reading of the following detailed description.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of inventive embodiments disclosed herein 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. Examples of constructions, materials, dimensions and fabrication processes are provided for select elements and all other elements employ that which is known by those skilled in the art. Embodiments will hereinafter be described in conjunction with appended drawings wherein like numerals/letters denote like elements. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations of this detailed description.

The present disclosure relates to constructions of, and systems including implantable medical electrical leads suitable for selective nerve stimulation, for example, stimulation of the sacral nerves. The implantable medical electrical lead may be temporary medical electrical lead that form a single conductor coil. The single conductor coil may be strained at least 300% or 400% and may not transmit a force greater than 0.1 lbf(0.4 N). The single conductor coil may be strained to elongated to three or four times its original coiled length without transmitting a force greater than 0.1 lbf(0.4 N) to a distal end of the single conductor coil. Thus, once implanted, the length of the coil can be stained to least 300% or 400% while not overcoming the fixation force of the distal end lead electrode. The distal end lead electrode does not migrate or dislodge from its implantation site even at high strain levels applied to the remaining coil length. While the present disclosure is not so limited, an appreciation of various aspects of the disclosure will be gained through a discussion of the examples provided below.

The conductor coil may be formed of a conductive material that exhibits the spring constant and elastic range described herein. The conductive cable forming the close wound conductor coil may have any useful configuration.FIG. 5illustrates a 1×19 configuration of the conductive cable where conductive filaments of the cable are arranged in a concentric lay, which is known in the art, where a single filament is surrounded by six filaments forming seven inner filaments and twelve outer filaments surround the seven inner filaments. Another useful configuration is a 1×7 configuration, where conductive filaments of the cable are arranged in a concentric lay, where a single filament is surrounded by six filaments. A further configuration is a 1×3 configuration.

The conductive cable may have a diameter in a range from about 0.004 inch to 0.008 inch (100 micrometers to 200 micrometers), or about 0.006 inch (150 micrometers). The conductive cable is tightly wound into a coil arrangement. The coil diameter may be from about 0.022 inch (560 micrometers) to about 0.045 inch (1140 micrometers), or from 0.034 inch (860 micrometers) to about 0.041 inch (1040 micrometers).

The conductor coil may be formed of a cobalt-nickel alloy such as a material commercially available under the trade designation MP35N. The conductor coil may be formed of an annealed or partially annealed stainless-steel material. The conductor coil may be formed beta-titanium alloy material.

The conductor coil or conductor cable may be formed of a beta-titanium alloy wire. Beta-titanium wire includes titanium with molybdenum, niobium, tantalum, zirconium, chromium, iron and tin. The beta-titanium wire or cable may be heated to a stress-relieve temperature of the beta titanium alloy to allow the wire or cable to retain a desired configuration while remaining ductile. The beta-titanium cable or wire may also be made with low resistance core materials to reduce the wire resistivity. The core materials can be Ta, Nb, Mo, W, Ag, Au. Two or more core materials may be used together.

One useful beta-titanium alloy is Ti-15Mo alloy material. The term “Ti-15Mo” refers to a metastable beta-titanium alloy that includes about 15 weight percent molybdenum. This Ti-15Mo alloy material is commercially available.

Four ETFE coated 1×7 cables (MP35N, annealed stainless steel, partially annealed stainless steel, and Ti-15Mo—each having a 0.006 inch (150 micrometers) diameter were wound into a coil having a diameter from 0.034 inch (860 micrometers) to 0.041 inch (1040 micrometers). Tensile, spring constant and elastic range tests were performed on each coil. The Ti-15Mo coil exhibited the lowest spring constant that was about 2.5 times lower than the MP35N coil. The Ti-15Mo coil had the highest elastic range that was about 4 times higher than the annealed stainless-steel coil.

The Ti-15Mo coil exhibited a spring constant of less than about 0.04 lbf/in (7 N/m) at a coil diameter in a range from about 0.034 to 0.041 inch (860 to 1140 micrometers). At a coil diameter of about 0.034 inch (860 micrometers) the Ti-15Mo coil exhibited a spring constant of about 0.04 lbf/in (7 N/m), and the remaining three coils (at 0.034 inch (860 micrometers) diameter) exhibited a spring constant of at least 0.08 lbf/in (14 N/m). At a coil diameter of about 0.041 inch (1040 micrometers) the Ti-15Mo coil exhibited a spring constant of about 0.02 lbf/in (3.5 N/m), and the remaining three coils (at 0.041 inch (1040 micrometers) diameter) exhibited a spring constant of at least 0.04 lbf/in (7 N/m).

The Ti-15Mo coil exhibited an elastic range of at least about 200% at a coil diameter in a range from about 0.034 to 0.041 inch (860 to 1140 micrometers). At a coil diameter of about 0.034 inch (860 micrometers) the Ti-15Mo coil exhibited an elastic range of at least about 210%, and the remaining three coils (at 0.034 inch diameter (860 micrometers)) exhibited an elastic range of less than about 110%. At a coil diameter of about 0.041 inch (1040 micrometers) the Ti-15Mo coil exhibited an elastic range of at least about 375%, and the remaining three coils (at 1040 micrometers (0.041 inch) diameter) exhibited an elastic range of less than about 150%.

The tensile curve of the four coils showed the Ti-15Mo coil had the lowest spring constant and largest elastic range. A low modulus coil is desired for the temporary medial electrical lead since it can be stretched with less resistance which will reduce lead migration. The Ti-15Mo coil had the lowest modulus of the four coils. Using a Ti-15Mo coil may reduce lead migration and increase lead life as compared to the four tested coils.

FIG. 2Ais a plan view of temporary medical electrical lead200, according to some embodiments.FIG. 2Aillustrates lead200including a single conductor coil210and a connector pin260, which together define an entire length of lead200, from a proximal end26of connector pin260to a distal-most tip21dtof lead200.

Conductor coil210is preferably close-wound along an entire length thereof, wherein the entire length of coil210is defined by a proximal portion210P thereof and a distal portion210D thereof. The close-wound nature of coil210can make lead200more responsive to push forces applied by an operator, in proximity to connector pin260, when implanting lead200, as described in greater detail below. According to the illustrated embodiment, coil proximal portion210P, which is coupled to connector pin260, extends within an outer sleeve216(for example, a medical grade polymer shrink tubing, such as Polyethylene Teraphthalate or Fluorinated Ethylene Propylene, or a combinations thereof), and coil distal portion210D extends distally from proximal portion210P to distal-most tip21dt, being inclusive thereof, with no turns of distal portion210D being mechanically coupled together.FIG. 2Afurther illustrates lead distal-most tip21dtbeing defined by a tapered segment21T of coil210, according to an embodiment described in greater detail below.

FIG. 2Bis a longitudinal section view of the coupling, or junction, between coil proximal portion210P and connector pin260, according to some embodiments.FIG. 2Billustrates coil proximal portion210P overlapping a distal section of connector pin260, for example, being soldered or welded thereto, and having the aforementioned sleeve216fitted thereabout, for example, via a heat shrink fit.

With further reference toFIG. 2A, in conjunction with the longitudinal section view ofFIG. 2C, coil distal portion210D includes an insulated proximal segment211N and an uninsulated distal segment21UN, wherein uninsulated distal segment21UN, which may have a length of about 2 to 5% of the total length of the lead200about 0.25 inch (6.35 millimeters) in some embodiments having a 12 inch (305 millimeters) lead length, functions as an electrode, for example, to stimulate the aforementioned sacral nerves when lead200is implanted as depicted inFIG. 1.

According to embodiments of the present invention, coil distal portion210D is configured to prevent uninsulated segment/electrode21UN from migrating or dislodging from the sacral nerve stimulation site over the course of the aforementioned stimulation evaluation, or trialing period, without the need for a fixation component, which may complicate the construction of lead200. With further reference toFIG. 1, we discovered that the part of lead200extending within the sacral region of the body, for example, in proximity to incision6, can be subject to surprisingly large strains (for example greater than 300%) induced by movement of the patient over the course of the trialing period, for example, as depicted in the schematics ofFIG. 3.

InFIG. 3, insulated proximal segment211N of lead200is shown extending through strata of skin S, fat F, and muscle M, in a sacral region, for example, the region adjacent to incision6. The schematic ofFIG. 3Arepresents an initial position of segment21N at the time of implant, while the schematics ofFIGS. 3B-Crepresent models (inspired by data collected from computerized tomography (CT) visualization of implanted metallic beads in human cadavers and live sheep, respectively) of potential strains imparted to lead211N by the movement of skin S, and fat F relative to the underlying muscle M.

In the cadaver studies, we found these strains to be higher than anticipated—for example, greater than 300%, or greater than 350% or greater than 400%. Thus, coil distal portion210D is preferably configured to absorb 300%, or 350% or 400% strain (in other words, elongate 400%) without transmitting a force that would cause uninsulated distal segment/electrode21UN to migrate, or dislodge from the sacral nerve stimulation site.

In animal studies, the lowest force recorded that initiated movement of uninsulated segment21UN was found to be about 0.135 lbf(0.6 N) so, according to preferred embodiments, coil distal portion2100translates a force of no greater than 0.1 lbf(0.4 N), or, preferably, less than 0.1 lbf(0.4 N), when subjected to a 300%, or 350%, or 400% strain.

FIG. 4is a plot of force, or load (lbf) versus extension (inches) for a sample from an exemplary embodiment of lead coil210that has a one-inch (25 millimeters) gauge length. The plot was generated by an Instron test system with a 10 lbf(44.5 N/m) load cell that elongated the sample at a pull rate of 3 inches/minute (76 millimeters/min), and the data point at 4 inches (102 millimeters) extension (400% strain or a total of 5 inches (127 millimeters) in length) is indicated at a force/load of less than 0.1 lbf(0.4 N). (Other data points are recorded at 75%, 120% and 150% strain.) The one-inch (25 millimeters) gauge length of the sample is un-deformed, or un-stretched coil extending between clamped stretched out ends, wherein the Instron clamps are spaced at least one inch from the one-inch length of un-stretched coil.

According to the exemplary embodiment, single conductor coil210of lead200is close wound from a single cable conductor32, for example, as depicted in the cross-section ofFIG. 5.FIG. 5illustrates cable conductor32including a plurality of conductive filaments320(for example, 0.0012 inch 20 micrometers) diameter medical grade 316L stainless steel wire) overlaid by an insulative layer302(for example, Ethylene Tetrafluoroethylene copolymer having a nominal thickness of 0.001 inch (25 micrometers)).

FIG. 5further illustrates conductive filaments320of cable32arranged in a 1×19 configuration, concentric lay, which is known in the art, wherein the arrows inFIG. 5indicate the left hand lay of seven inner filaments and the right hand lay of twelve outer filaments of filaments320.

To provide uninsulated distal segment21UN of coil distal portion210D, as well as the uninsulated section of coil proximal portion210P that overlaps connector pin260, insulative layer302is removed from around conductive filaments320by any suitable process known in the art. With further reference toFIGS. 2B-C, coil distal portion210D defines an innermost surface of lead200that surrounds an elongate lumen201of lead200, wherein an elongate bore of connector pin260defines a proximal-most portion of lead lumen201and a proximal opening thereof at pin proximal end26(FIG. 2A).

Furthermore, according to the illustrated embodiment, insulative layer302of cable32serves as a primary insulation for lead200and defines both the innermost surface of lead200and an outermost surface of lead200along insulated segment211N of coil distal portion210D. Thus, as indicated above, no turns of coil distal portion210D are mechanically coupled together so that coil distal portion210D can freely stretch and absorb the strain, as described above, without translating a force that can dislodge uninsulated distal segment21UN. Lumen201may be sized to receive a stylet400, which is described in greater detail below, in conjunction withFIGS. 7A-C.

According to some preferred embodiments, single cable conductor32is close wound to form lead200with a maximum diameter larger than that of a typical temporary medical electrical lead for sacral nerve stimulation, for example, being between 0.032 inch (813 micrometers) and 0.041 inch (1040 micrometers) along insulated segment211N of coil distal portion210D. This larger diameter of lead200, in conjunction with material selection and the close-wound pitch of coil conductor210, contributes to the relatively low force translated along coil distal portion210D (lower than that of a typical temporary lead) when strained up to 400%, as described above.

In addition to providing strain relief that prevents uninsulated segment/electrode21UN from dislodging from the sacral nerve stimulation site, the configuration of lead200facilitates removal thereof from the patient's body when the trialing period is complete by allowing an operator who explants lead200to stretch coil210to a smaller diameter with relative ease. Furthermore, as indicated above, the lack of a fixation component in the construction of lead200also allows for an easier removal of lead200.

To further facilitate removal, and with reference toFIG. 6A, distal-most ends320feof conductive filaments320of cable32, located at distal-most tip21dtof lead200(FIG. 2A), are free of any mechanical coupling that could cause distal-most tip21dtof lead200to enlarge by a ‘bunching up’ of cable filaments320, due to differing filament lengths of the above-described 1×19 configuration of cable32, as coil210is stretched during explant.

FIG. 6Billustrates cable filament distal-most ends320cethat are mechanically coupled together by a laser weld, according to the typical practice known in the art, when a coil formed from the 1×19 cable is stretched. Such a ‘bunching up’ has been found to increase the difficulty of explant by catching on tissue as the cable is pulled along the explant path.

FIG. 7Ais a plan view of a system100for providing temporary medical electrical stimulation, which includes the above-described lead200.FIG. 7Aillustrates system100including an introducer needle600, the aforementioned stylet400, and a grip tool500for temporarily securing stylet400to lead200, for example, when an operator inserts lead200through introducer needle600for implant, for example, as illustrated in the schematic ofFIG. 8.

According to the illustrated embodiment, introducer needle600has a lumen610sized to receive passage of the entire length of the temporary medical electrical lead200(for example, about 305 millimeters (12 inches)) therethrough, from a proximal opening611of needle lumen610to a distal opening612of needle lumen610; and, according to an exemplary embodiment, introducer needle is a 18.5 gauge needle that may have a length of about 89 micrometers (3.5 inches) or a length of about 127 micrometers (5 inches).

FIG. 7Afurther illustrates lead200including markers230d,230ppositioned along coil distal portion210D to provide the operator with visual indicators of locations of lead distal-most tip21dt, relative to needle lumen distal opening612, as the operator advances lead200through needle lumen610for implant. According to an exemplary embodiment, a length of each marker230d,230pis about 0.1 inch (25 millimeters), marker230dis spaced about 4.3 inches (109 millimeters) from distal-most tip21dt(for example, for use with the aforementioned 3.5 inch (89 millimeters) long needle), and marker230pis spaced about 5.8 inches (147 millimeters) from distal-most tip21dt(for example, for use with the aforementioned 5 inch (127 millimeters) long needle). To allow coil distal portion210D to freely stretch, as described above, markers230d,230pare constructed in a manner so that they do not mechanically couple turns of coil distal portion together, for example, by laser marking insulative layer of302of cable conductor32. When insulative layer302is formed from Ethylene Tetrafluoroethylene copolymer that is loaded with a Titanium dioxide pigment, the laser marking darkens the white appearance of the loaded copolymer.

With further reference toFIG. 7A, stylet400includes a proximal length40P and a distal length40D. Distal length40D has an outer diameter sized to fit in sliding engagement within elongate lumen201of lead200(FIG. 7B), and proximal length40P has an outer diameter sized to abut proximal end26of lead connector pin260, when distal length40D is fitted within lead lumen201, for example, at a shoulder460of stylet400, which is a transition between proximal length40P and distal length40D.

FIG. 7Bis a longitudinal section view of a portion of lead200at distal-most tip21dtthereof, which shows stylet distal length40D, having been inserted into lead lumen201at the proximal opening thereof (connector pin proximal end26) per arrow A ofFIG. 7A. According to some methods and embodiments, as an initial step in assembling system100, stylet400is inserted into lead lumen201until stylet distal length40D abuts lead distal-most tip21dt, as shown, being stopped by the aforementioned tapered segment21T of lead coil210. Tapered segment21T decreases in diameter, for example, over a length of no more than about 0.04 inch (102 millimeter), to an inner diameter that prevents stylet distal length40D from protruding out from distal-most tip21dtof lead200.

Arrow B inFIG. 7Aindicates a next step in assembling system100, according to some methods, that involves securing lead200to the inserted stylet400by fitting a distal portion50D of grip tool500around lead connector pin260and a proximal portion50P of grip tool500around proximal length40P of the inserted stylet400. The above-described relatively low force translated along coil distal portion210D of lead200when strained up to 400%, due in part to the larger than typical diameter thereof, makes lead200significantly limp relative to a stiffness of a of stylet distal length40D that has a larger than typical diameter corresponding to the larger diameter of lead coil210. Thus, if grip tool500were not employed to secure lead200to the inserted stylet400, the operator may encounter difficulty in keeping lead200from sliding off of stylet400when inserting distal-most tip21dtof lead200into stylet lumen610for implant.

The portions of grip tool500are preferably fitted around lead200and the inserted stylet400so that connector pin proximal end26abuts stylet proximal length40P. Furthermore, grip tool500is shown having a window560formed along an intermediate portion50intthereof (between distal portion50D and proximal portion50P), so that, when grip tool500is fitted, grip tool intermediate portion50intcan be located in proximity to the abutment of connector pin proximal end26with stylet proximal length40P, thereby exposing lead connector pin260through window560, as shown inFIG. 7C.

FIG. 7Dis a perspective view of grip tool500, according to some embodiments, wherein a means for the fitting of grip tool500, as described above, is shown.FIG. 7Dillustrates grip tool500including an elongate channel505extending along an entire length of tool500, from a proximal end501thereof to a distal end502thereof, wherein channel505is sized to receive, in gripping engagement, lead200and stylet400.FIG. 7Dfurther illustrates grip tool500including an elongate slot515extending along channel505to provide access thereto for insertion and withdrawal of stylet400and lead200. According to an exemplary embodiment, grip tool500may be formed, for example, from a medical grade silicone rubber by any suitable molding process known in the art.

FIG. 8is a schematic showing introducer needle600positioned in the patient's body, with lumen distal opening612located in proximity to one of the sacral foramina4.FIG. 8further illustrates lead200, with inserted stylet400secured thereto by grip tool500, having been advanced through needle600until distal-most tip21dtof lead200exits needle lumen distal opening612.

According to some methods, the operator grips grip tool500to advance lead200through needle600and through foramen4until lead distal-most tip21dtis located in proximity to the sacral nerves. The aforementioned close-wound construction of lead coil210makes distal-most tip21dtresponsive to the operator's push force applied in proximity to lead connector pin260, and assures that the above-described markers230d,230pprovide an accurate indication of the location of tip21dtrelative to needle lumen distal opening612. Then, to determine if uninsulated distal segment/electrode21UN of lead200is positioned properly to stimulate the sacral nerves, the operator may connect an external pulse generator to lead connector pin260through window560of grip tool500, or may remove grip tool500prior to making the connection.

In either case, after determining that lead200is properly positioned and with grip tool500removed, to remove introducer needle600from around lead200, the operator can retract introducer needle600while applying a push force to lead200with the inserted stylet400, which push force is transferred to lead200by the aforementioned abutment of stylet proximal length40P with lead connector pin proximal end26. Thus, it may be appreciated that a diameter of stylet proximal length40P is such to fit in sliding engagement within needle lumen610so that needle600can be retracted over stylet400as well as over the implanted lead200. Furthermore, the above-described close-wound construction of lead coil210can provide tactile feedback to the operator that lead200is not advanced out of position by the push force applied to stylet400as the operator retracts needle600.

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.