Abstract:
A multi-conductor lead body having improved mechanical characteristics and improved manufacturability is disclosed. The lead body includes multiple conductors wound around a generally cylindrical or tubular, insulative core member. Ones of the conductors are spaced from other ones of the conductors by means of insulative strands or tubes wound around the core intermediate the conductors. The conductors may be stranded or cabled conductors. The core may be an insulative cylindrical or tubular member having a centrally located tensile reinforcement member, or may take the form of an insulated coiled conductor, allowing the use of a centrally located stylet to place the lead. Preferably, conductors and insulative strands or tubes separating the conductors are sized relative to the core member such that a gap is allowed between the conductors and associated insulative strands or tubes. In one embodiment, at least one of the conductors may be electrically and mechanically coupled to one or more electrodes such as a defibrillation electrodes. The electrodes may each be may be positioned along a respective portion of the outer surface of the conductor. Openings fashioned in the jacket of the lead body expose the electrodes so that the outer surface of the electrodes is substantially adjacent to the outer surface of the lead body, thus providing a lead body having minimal dimensions.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to body implantable biomedical leads and more particularly to multi-conductor leads. 
     In the field of implantable electrical leads, a wide variety of configurations have been employed and proposed for providing multi-conductor lead bodies. The two most widely employed approaches are the coaxial design, wherein multiple coiled conductors are mounted around one another, separated by tubular insulative sheaths, as described in U.S. Pat. No. 4,355,646 issued to Kallok and the multi-lumen design, wherein the lead body takes the form of a multi-lumen tube, each lumen carrying a separate conductor, as disclosed in U.S. Pat. No. 5,584,873 issued to Shoberg, et al. Additional alternative approaches have included embedding multiple conductors within the wall of an insulative lead body, as disclosed in U.S. Pat. No. 5,968,087 issued to Hess, et al., U.S. Pat. No. 5,016,646 issued to Gotthardt, et al. and U.S. Pat. No. 5,845,396 issued to Altman et al. An additional alternative approach is disclosed in U.S. Pat. No. 5,935,159 issued to Cross et al, in which individual conductors are separated from one another by means of a central strut having laterally extending projections, serving to space and insulate adjacent conductors from one another, within a tubular outer sheath. 
     Notwithstanding the variety of lead body designs that have been proposed, there is still a desire to improve the mechanical characteristics and the producability of multiple conductor lead bodies. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward providing a multi-conductor lead body having improved mechanical characteristics and improved manufacturability. Lead bodies according to the present invention are manufactured by winding multiple conductors around a generally cylindrical or tubular, insulative core member, and by spacing adjacent ones of the conductors from one another by means of insulative strands or tubes, wound around the core intermediate the conductors. In preferred embodiments of the invention, the conductors may take the form of stranded or cabled conductors, as described in U.S. Pat. No. 5,584,873 issued to Shoberg, et al., cited above and incorporated herein by reference in its entirety. In some embodiments, the core may take the form of an insulative cylindrical or tubular member having a centrally located tensile reinforcement member. In these embodiments, the insulative member may be extruded over the tensile member. In other embodiments, the core may take the form of an insulated coiled conductor, allowing the use of a centrally located stylet to place the lead. In these embodiments, the insulative coating of the coiled conductor may be formed as a separate tubular member or may be extruded in one or two layers, as is desired. 
     Preferably, the conductors and insulative strands or tubes separating the conductors are sized relative to the core member such that a gap is allowed between the conductors and associated insulative strands or tubes may be physically displaced under loading, improving the crush resistance and durability of the lead bodies. In embodiments employing tubular insulative members separating adjacent conductors, the tubes serve a function similar to that of the compression lumens described in the above-cited Shoberg, et al. patent, further facilitating the ability of the lead to withstand damage due to compression. 
     According to another aspect of the invention, at least one of the conductors may be electrically and mechanically coupled to an electrode. The electrode may be a defibrillation electrode of the type used in an implantable medical device, and the coupled conductor may be a high-voltage conductor. The electrode may be of an elongated configuration, and positioned along the outer surface of a portion of the conductor. Alternatively, multiple electrodes of this nature may each be positioned along a respective portion of the at least one of the conductors. Openings such as slits fashioned in the jacket of the lead body expose the electrodes so that the outer surface of the electrodes is substantially adjacent to the outer surface of the lead body. This configuration provides a lead of minimal size. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of an endocardial lead in which the present invention may be implemented. 
     FIG. 2 is a cross section of a first type of conductor that may be used in practicing the present invention. 
     FIG. 3 is across section of a second type of conductor that may be used in practicing the present invention. 
     FIG. 4 is a cross section of the lead body taken along lines [ 4 — 4 ] of FIG.  1 . 
     FIG. 5 is a cross section of the lead body of a first alternative embodiment of the present invention. 
     FIG. 6 is a cross section of the lead body of a second alternative embodiment of the present invention. 
     FIG. 7 is a cross section of the lead body of a third alternative embodiment of the present invention. 
     FIG. 8 is a cross section of the lead body of a fourth alternative embodiment of the present invention. 
     FIG. 9 is a cross section of the lead body of a fifth alternative embodiment of the present invention. 
     FIG. 10 illustrates an alternative embodiment of a trilumen tube lead body. 
     FIG. 11 is a cross-sectional view illustrating yet another configuration of the lead body of the current invention. 
     FIG. 12 is a top view of the lead body shown in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a plan view of an exemplary embodiment of an endocardial lead in which the present invention may usefully be practiced. The lead illustrated is a four conductor lead, having an elongated tubular insulative lead body  10 , carrying a connector assembly  12  at its proximal end. Connector assembly  12  is provided with four connector rings  14 ,  16 ,  18  and  20 , each coupled to one of the conductors within lead body  10 . Connector assembly  12  may correspond to that issued in U.S. Pat. No. 5,843,141 issued to Bischoff, et al, and incorporated herein by reference in its entirety. Electrodes  22  and  24  are coiled defibrillation electrodes, of conventional types, which may be spaced along lead body  10  to facilitate their location, for example, in the superior vena cava and right ventricle of the heart, respectively. In some embodiments, electrodes  22  and  24  may be embedded in lead body  10  to provide an isodiametric lead configuration, as disclosed in U.S. Pat. No. 4,161,952 issued to Kinney et al, or U.S. Pat. No. 5,957,970 issued to Shoberg, et al., both also incorporated herein by reference in its entirety. At the distal end of the lead, lead body  10  carries a ring electrode  26  and a tip electrode  28  which may be used for cardiac pacing and sensing of heart depolarizations. Tines  30 , or alternatively, a screw, may be employed to retain electrode  28  in contact with hearttissue. Electrodes  22 ,  24 ,  26  and  28  are each coupled to one of connectors  14 ,  16 ,  18  and  20  by means of one of four mutually insulated conductors located within lead body  10 . 
     FIG. 1 is intended to be purely exemplary of the type of lead in which the invention may usefully be practiced. Other electrode or connector types may of course be substituted. Additional electrodes may be added, or electrodes may be deleted. In addition, it should also be understood that the lead body of the present invention is useful in the context of leads carrying one or more physiologic sensors, for example, carrying an oxygen sensor as disclosed in U.S. Pat. No. 4,903,701 issued to Moore et al, a pressure sensor as disclosed in U.S. Pat. No. 4,967,755 issued to Pondorf or a temperature sensor as disclosed in U.S. Pat. No. 5,081,988, issued to Cook, et al., all of which patents are incorporated herein by reference in their entireties, or carrying any other physiologic sensor. As the number of electrodes and/or sensors increases, the required number of mutually insulated conductors within the lead body correspondingly increases. In general, a lead body according to the present invention is especially desirable in leads employing larger numbers of conductors, e.g., 3 conductors, 4 conductors, or more. However, the lead body design according to the present invention may also be usefully employed in leads having as few as two conductors. 
     FIG. 2 is a cross-sectional view of a first conductor type that may be usefully employed in conjunction with the present invention. This conductor type, like that described in U.S. Pat. No. 5,760,341 issued to Laske et al and incorporated herein by reference in its entirety, employs a  49  strand cable  40  as the conductive element, and is provided with a single or multiple layer insulative overcoating  42  which may be extruded over cable  40 . Conductor  42  as illustrated also corresponds generally to the conductors described in the above cited Shoberg, et al. patent and to the stranded conductors presently employed in commercially marketed Sprint TM leads, manufactured and sold by Medtronic, Inc. 
     FIG. 3 illustrates an alternative embodiment of a conductor appropriate for use in conjunction with the present invention. In this embodiment, the conductor  34  includes a stranded conductor  44  consisting of seven strands, covered by an extruded insulative coating  46 . This conductor design corresponds to that disclosed in U.S. Pat. No. 5,246,014 issued to Williams et al, also incorporated heroin by reference in its entirety. Other conductor types may of course also be employed, including  20  strand cables, as described in U.S. Pat. No. 5,845,396 issued to Altman et al, also incorporated herein by reference in its entirety. In still other embodiments, the individual conductors may simply take the form of a single filar wire conductor, wound around the core member of the lead body. It should also be noted that while all of the conductors illustrated in the present specification are individually insulated, in some embodiments of the invention, uninsulated conductors may alternatively be employed, such that the insulative strands or tubes wound around the core member between the individual conductors may serve as the only means of insulating adjacent conductors from one another. 
     FIG. 4 is a cross-section through the lead of FIG. 1, illustrating a preferred embodiment of the present invention. As illustrated, lead body  10  takes the form of a tubular insulative sheath, in which an insulative core member  38  is centrally located. Core member  38  may be fabricated of silicone rubber, polyurethane or other biocompatible plastic. Core member  38  optionally includes a tensile reinforcement member  48 , which may take the form, for example of a polyester cord. Alternatively, core  38  might include an open central lumen, or might be a solid cylindrical strand of plastic. Located between core  38  and tubular lead body  10  are four conductors  32 , which in this case correspond to conductor  32  as illustrated in FIG.  2  and take the form of insulated cabled conductors like those described in the above-cited Shoberg, et al. and Laske, et al. patents. Conductors  32  are preferably wound around core member  38  using a conventional winding machine, and are separated from one another by insulative strands  36 , similarly wound around core  38 , and formed of biocompatible insulative polymers such as polyurethane, silicone rubber, or the like. Preferably, the conductors  32 , strand  36 , and tubular lead body  10  are dimensioned such that there is some space between the conductors  32  and their adjacent strands  36 , to allow for some displacement of the strands and conductors when the lead body is loaded or flexed. 
     FIG. 5 is a cross-section through a first alternative lead body configuration according to the present invention. In this embodiment, the tubular. lead body  10 A surrounds an insulative core  50  having an optional reinforcing strand  52 , similar to that described in conjunction with FIG.  4 . In this particular embodiment, five conductors  54  are provided which may, for example, take the form of seven stranded conductors as illustrated in FIG. 3, a 19 stranded conductor as illustrated in the above-cited Altman et al patent, or a 49 stranded conductor as illustrated in FIG.  2 . Similar to the design illustrated in FIG. 4, adjacent conductors  54  are separated by insulative strands  56  which are wound around core  50  intermediate the conductors  54 . Additional numbers of conductors, for example six, seven, eight or more may be provided in alternative embodiments of a lead body as illustrated in FIG.  5 . 
     FIG. 6 illustrates a second alternative embodiment of a lead body according to the present invention, which might be employed in conjunction with a lead body  10 B carrying only two mutually insulated conductors. In this embodiment, four individual conductors  64   a  and  64   b  are provided which may correspond to any of the conductor types discussed previously. In this embodiment, the conductors are arranged in a first pair comprising conductors  64   a  and a second pair comprising conductors  64   b . The pairs of conductors are separated from one another by insulative strands  66 , wound around core  60 . The conductors in each of the pairs are connected in common to a connector at the proximal end of the lead body and to an electrode or other electrical component mounted to the lead body and thus do not require the insulative properties that would be provided by an insulated strand located therebetween. As in the embodiments illustrated in FIGS. 4 and 5, the insulative strands  66  and conductors  64   a ,  64   b  are preferably dimensioned so that there is space between them, allowing for displacement of the conductors and strands while the lead is bent or loaded. 
     FIG. 7 illustrates a third alternative embodiment of a lead according to the present invention. In this embodiment, the core within lead body  10 C takes the form of a coiled conductor  72  surrounded by an insulative sleeve  70  which may be formed as a separate tubular part or extruded over coil  72 . The insulating sleeve  70  may be fabricated of any suitable biocompatible material, including silicone rubber, polyurethane, or the like. Particularly in embodiments employing a central coil as illustrated, the insulative sleeve  70  may comprise PTFE or ETFE, extruded directly over coil  72 . Conductors  74  and insulative strands  76  may correspond to insulative strands and conductors as described in conjunction with FIGS. 4-6 above, and are wound around the core comprising coil  72  and insulative tubing  70  in the same fashion as described in conjunction with FIG.  4 . 
     FIG. 8 illustrates a fourth alternative embodiment of a lead body according to the present invention. In this embodiment, the core located centrally within tubular lead body  10 D takes the form of a central coil and an insulative sleeve or covering  80 , as described generally in conjunction with FIG. 7 above. In this embodiment, however, the insulative strands are replaced by insulative tubes  86 , located between selected ones of the insulated conductors  84   a ,  84   b ,  84   c . Tubes corresponding to tubes  86  could of course likewise be employed as substitutes for the insulative strands as illustrated in FIGS. 4-7, discussed above. Such tubes possess an increased ability to flex under stress, thereby increasing the crush performance of the lead body. 
     In the particular embodiment illustrated, it will be noted that five conductors are provided, including two pairs  84   a ,  84   b  of conductors not separated by insulative tubes  86  and a single conductor  84   c , separated from the adjacent pairs of conductor by insulative tubes  86 . In this particular embodiment, the central coil  82  may serve as a conductor coupled to a tip electrode, sized to allow placement of a stylet through the central lumen within the coil, to facilitate lead placement. Each of the two pairs of conductors  84   a ,  84   b  might be coupled to a separate defibrillation electrode, e.g., an SVC defibrillation electrode corresponding to  22  in FIG. 1 and a right ventricular electrode corresponding to electrode  24  in FIG.  1 . The unpaired conductor  84   c  may be coupled to a ring electrode such as electrode  26  in FIG.  1 . In configurations as illustrated in FIG. 8, for higher voltage applications, conductors may be provided in pairs, triplets or the like, coupled to a single connector on the proximal end of the lead body and to a single electrode or other electrical component elsewhere on the lead body. This conductor configuration provides increased reliability and decreased resistance. As the conductors are coupled in common in such cases insulated strands or tubes are not required therebetween. Such pairs or triplets of conductors, however, would be separated from adjacent individual conductors, pairs or triplets of conductors, by means of insulated tubes or strands. 
     In the particular embodiment illustrated in FIG. 8, the central coil  82  might be an MP35N coil having a wire diameter of 0.003 inches, and defining a central lumen of 0.017 inches. The insulation  80  covering coil  82  may take the form of an extruded coat of ETFE or PTFE having a thickness in the range of 0.0015 through 0.003 inches. In the preferred embodiment, a PTFE coat having a thickness of 0.0015 inches is utilized. In an alternative embodiment, an ETFE coat having a thickness of about 0.003 inches is used. The conductors  84   a ,  84   b ,  84   c  may take the form of 49 strand cables, as discussed in conjunction with FIG. 2, having an outer cable diameter of 0.0065 inches, covered with two insulative coatings of 0.003 inches each, which may take the form of a high dielectric strength inner coating of Genemer polymer, manufactured by the Virginia Power and Light Company, silicone rubber, or ETFE with an outer coating of ETFE. The outer diameter of lead body  10 D may be approximately 6 French (0.078 inches) and may have a wall thickness of 0.01 inches. Lead body  10 D may be fabricated for example of urethane or silicone, and may take the form of a separately fabricated tube or may be extruded over the conductors  84  and tubes  86 , after they have been wound around the core ( 80 ,  82 ). Tubes  86  are preferably fabricated of a biocompatible polymer such as polyurethane or silicone rubber having material hardness and flow resistance less than or equal to the insulative coating applied to the conductors  84 , in order to reduce stress concentration and cold flow of the insulative coating on conductors  84 . The tubes  86  may have outer dimensions corresponding to the outer dimensions of the conductors  84 . In a lead body dimensioned as described, the sizing of the conductors and tubes relative to the core ( 80 ,  82 ) would allow for placement of nine similarly sized tubes or conductors, wound around the core ( 80 ,  82 ). However, as only eight tubes and conductors are employed, a substantial space is left to allow for shifting of the conductors and tubes during flexing or loading of the lead body, as is desired. 
     FIG. 9 illustrates that the conductor configuration of the present invention may also be employed in composite designs, in which other conductor configurations are also employed. In this embodiment, lead body  10 E takes the form of a trilumen tube. In a first lumen, a conductor assembly according to the present invention is provided, including a core  90  with an optional reinforcing strand  92 , four conductors  94  and four insulative strands  96 , generally corresponding to the arrangement illustrated in FIG.  4 . Located in the other two lumens are a coiled conductor  98  of conventional design and a stranded or cabled conductor  100 . In such a design, for example, the coiled conductor  98  may connect to a tip electrode and allow for the passage of a stylet though the lead body. Cabled conductor  100  might be coupled, for example, to a high voltage electrode, while conductors  96  may be coupled to low voltage components, such as cardiac pacing and sensing electrodes and/or physiologic sensors such as oxygen sensors, temperature sensors and the like. 
     FIG. 10 illustrates an alternative embodiment of a trilumen tube lead body. In this embodiment, two lumens provide a conductor assembly according to the present invention. Each conductor assembly includes a core  90  which may contain an optional reinforcing strand  92  of the type shown in FIG.  9 . Each conductor assembly is further shown to include three conductors  94  and three insulative strands  96 , although other variations are possible, including those discussed above. The third lumen contains a coiled conductor  98  of conventional design, but could alternatively be a stranded or cabled. conductor  100  such as shown in FIG.  9 . 
     FIG. 11 is a cross-sectional view illustrating yet another configuration of the lead body of the current invention. This embodiment includes two defibrillation electrodes  102 , each shown positioned on top of an associated conductor  104 . Each of the conductors  104  is a high-voltage defibrillation cable, which may be constructed of MP35N. Each defibrillation electrode  102 , which is formed of a bio-compatible metal, is shown attached to the respective conductor  104  using coupling devices such as clamps  105  which may be constructed of a biocompatible polymer or metal. Slits are formed within the insulative jacket  106  of the lead body to accommodate the defibrillation electrodes. A slit of this nature could be formed, for example, using a material-selective laser with a vision system adapted to remove only the insulative material. 
     The electrode configuration of FIG. 11 significantly decreases the size of the lead body as compared to prior art designs. Defibrillation electrodes are generally coiled around the outer diameter of the lead body insulation. For example, FIG. 1 shows defibrillation electrodes  22  and  24  coiled on the outside of lead body  10 . The electrodes thereby increase the overall dimensions of the lead. By positioning a defibrillation electrode  102  directly on top of conductor  104  within a slit within the insulative jacket as shown in FIG. 11, the size of the lead body may be decreased by approximately  1  French. 
     In one embodiment, the surface area of defibrillation electrodes  102  is increased using a sintering process, or by mounting fin-like structures  108  on the outside surface of a defibrillation electrode. This decreases the current density during treatment, and thereby minimizes the chance of plasma generation. 
     FIG. 11 further includes additional conductors  110  which may be configured in any of the manners discussed above. The conductors are separated from one another via the insulated strands or tubes  112  in the manner discussed above. 
     Centrally-located core member  114  is also shown, and may be of any of the constructions discussed in the foregoing paragraphs. Finally, it may be noted that although the current example includes two defibrillation electrodes, thereby providing the advantage of redundancy, the lead body could be adapted to include one defibrillation electrode, or more than two electrodes. 
     FIG. 12 is a top view of the lead body shown in FIG.  11 . This view shows the manner in which defibrillation cables  102  are exposed at the external surface of lead body via slits in insulative jacket  106 . Multiple defibrillation electrodes may be coupled to a single conductor  104 , as illustrated by defibrillation electrodes  102   a  and  102   b . This view further illustrates the use of clamps  105  to maintain the position of defibrillation cables  102  on top of conductors  104 . Other types of mating devices could be used to achieve this coupling. The spiral configuration of the conductors around core member  114  is also visible from this illustration. This spiral configuration may be wound using any pitch. Finally, if desired, adhesive material may be used to form a seal around the slits. This adhesive could be applied between insulative jacket  106  and the inner elements of the lead body, including conductors  108  and  110 , and insulated strands or tubes  112 . 
     As illustrated above, the lead body configuration provided by the present invention, comprising a plurality of conductors wound around an insulative core, spaced from one another by means of insulative tubes or strands, provides a highly flexible lead body design which may be adapted to a wide variety of lead designs employing multiple conductors. The design of the lead body, employing conductors wound around the central core by means of a winding machine and insulative coatings that may be formed separately as tubes or extruded over underlying subassemblies also provides opportunities for substantial simplification of the manufacturing process for the lead body.