Abstract:
A medical lead includes a lead body and an electrode formed by a plurality of coil turns and positioned about the lead body. A portion of a conductor extends from an internal lumen of the lead body, through an opening, to an external surface of the lead body, to electrically couple with the electrode; the portion of the conductor is press fit between at least one of the plurality of turns of the electrode and the lead body thereby making direct electrical contact with the electrode.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates generally to electrical leads for use with implantable medical devices, and more particularly to electrical coupling between a conductor and an electrode of such medical leads.  
         BACKGROUND OF THE INVENTION  
         [0002]    Implantable defibrillation leads typically include an electrode in the form of a high-voltage defibrillation coil. This coil is electrically coupled to an associated high-voltage conductor coil or cable that extends through the lead body. Pacing leads, cardiac catheters, muscle stimulation leads, and other electrode bearing leads may also employ similar coil/conductor arrangements.  
           [0003]    Many techniques such as welding, crimping, brazing, swaging, etc., have been proposed/utilized for producing the necessary electrical interconnections between the defibrillation coil and the high-voltage conductor. Obviously, such interconnections must be reliable and possess desirable mechanical properties. For example, U.S. Pat. No. 5,676,694 entitled “Medical Electrical Lead”, issued Oct. 14, 1997 and assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference, discloses a connection mechanism wherein the coil is electrically coupled to the high-voltage conductor by means of a conductive crimp-sleeve fabricated from a conductive biocompatible metal such as titanium, stainless steel, tantalum or platinum. A portion of the conductor insulation is stripped away and inserted into a longitudinal lumen through a tubular portion of the crimp-sleeve. The tubular portion is attached to the conductor by means of a plurality of crimps spaced around the circumference of the tubular portion. An end portion of the coil is welded or brazed to the sleeve to provide electrical coupling between the coil and the conductor.  
           [0004]    Traditional means employed to couple electrodes to conductors, such as those described in the above-cited patent, require additional components (i.e. crimping/weld sleeves) and/or manufacturing steps (e.g. crimping, welding, etc.), whereas embodiments of the present invention accomplish direct electrical coupling between a conductor and an electrode. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The following drawings are illustrative of particular embodiments of the invention and therefore do not limit its scope, but are presented to assist in providing a proper understanding of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. The present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements, and:  
         [0006]    [0006]FIG. 1 is a plan view of an implantable lead assembly in accordance with an embodiment of the present invention;  
         [0007]    [0007]FIG. 2 is a radial cross-sectional view of the lead assembly shown in FIG. 1 taken along line  2 - 2 ;  
         [0008]    [0008]FIG. 3 is an axial cross-sectional view of a portion of a lead assembly in accordance with another embodiment of the present invention;  
         [0009]    [0009]FIG. 4 is a plan view of the embodiment shown in FIG. 3;  
         [0010]    [0010]FIG. 5A is an axial cross-sectional view of a portion of a lead assembly in accordance with yet another embodiment of the present invention;  
         [0011]    [0011]FIG. 5B is an axial cross-sectional view of a portion of a lead assembly in accordance with yet another embodiment of the present invention;  
         [0012]    [0012]FIG. 6 is a plan view of the embodiment shown in FIG. 5A;  
         [0013]    [0013]FIG. 7 is a radial cross-sectional view illustrating a first alternative configuration of the embodiment shown in FIGS.  5 A-B and FIG. 6;  
         [0014]    [0014]FIG. 8 is a radial cross-sectional view illustrating a second alternative configuration of the embodiment shown in FIGS.  5 A-B and FIG. 6;  
         [0015]    [0015]FIG. 9 is an axial cross-sectional view of a portion of a lead assembly in accordance with yet another embodiment of the present invention; and  
         [0016]    [0016]FIG. 10 is a plan view of the embodiment shown in FIG. 9. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    The following 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 a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described herein without departing from the scope of the invention.  
         [0018]    [0018]FIG. 1 is a plan view of an implantable lead assembly in accordance with an embodiment of the present invention. The lead of FIG. 1 includes an elongated insulative lead body  10  fabricated, for example, of silicone rubber, polyurethane or other biocompatible elastomer. At a distal end  200  of the lead, there is carried an elongated defibrillation coil  12 , a ring electrode  14 , and a tip electrode  16 . Tines  18  are provided to maintain electrode  16  in contact with the tissue of the right ventricle. Alternatively, a helix tip electrode, such as is commonly known to those skilled in the art, may be employed in place of tip electrode  16  and tines  18 . Electrodes  14  and  16  correspond to any conventionally available pacing and sensing electrodes and are coupled to connector contacts, carried in a bipolar connector leg  24  extending from a bifurcation  20  at a proximal end  100  of lead body  10 , via elongated conductors  54  and  58  (FIG. 2), respectively. Likewise, electrode  12  corresponds to any conventionally available defibrillation electrode and is coupled to a connector pin  30 , carried by a unipolar connector leg  22  extending from bifurcation  20  at proximal end  100  of lead body  10 , via an elongated conductor including a first conductor portion  561  extending within lead body  10  and a second conductor portion  562  extending between electrode  12  and lead body  10 . According to embodiments of the present invention, first conductor portion  561  coupled to connector pin  30  extends to second conductor portion  562 , which exits lead body  10  to electrically couple with electrode  12 , being held between electrode  12  and lead body  10 . Although FIG. 1 illustrates second conductor portion  562  extending beneath a plurality of coil turns of electrode  12 , the present invention allows alternative configurations wherein second portion  562  is held beneath a single turn of electrode  12 . Furthermore, in alternate embodiments, several coil turns of electrode  12 , at each end of electrode  12 , may be welded together.  
         [0019]    [0019]FIG. 2 is a radial cross-sectional view of the lead assembly shown in FIG. 1 taken along line  2 - 2 , wherein lead body  10  is illustrated as a multi-lumen lead body of the type shown and described in U.S. Pat. No. 5,584,873 entitled “Medical Lead Compression Lumens”, issued Dec. 17, 1996 and assigned to the assignee of the present invention, the teachings of which are hereby incorporated by reference. As illustrated in FIG. 2, lead body  10  includes conductor lumens  40 ,  42 , and  44  carrying conductors  561 (first portion),  54  and  58 , respectively, wherein conductors  561  and  54  are in the form of generally straight, bundled stranded wire cables and conductor  56  is in the form of a coiled conductor. Wires forming conductors  561 ,  54  and  56  may be made of MP35-N alloy, well known in the art, or any other biostable and biocompatible material that is capable of reliably conducting electrical current after having been subjected to numerous, repeated bending and torsional stresses. FIG. 2 further illustrates lead body  10  including compression lumens  46 ,  48 , and  50 , as taught in the &#39;873 patent, which are not necessary elements according to embodiments of the present invention.  
         [0020]    [0020]FIG. 3 and FIG. 4 are cross-sectional and plan views respectively of a portion of an implantable lead assembly in accordance with an embodiment and of the present invention. FIG. 3 illustrates first conductor portion  561  extending distally within lumen  42  to a first opening  62  in proximity to a proximal end  60  of the lead assembly portion shown; second conductor portion  562  extends out first opening  62  to be positioned between lead body  10  and coil electrode  12  and then re-enters lumen  42  via a second opening  64  positioned in proximity to a distal end  66  of the lead assembly portion shown. Embodiments of the present invention include first opening  62  and second opening  64  positioned as illustrated in FIG. 4 but also include alternate positions of openings  620 ,  640  as indicated by dashed lines located more toward a middle portion of electrode  12 . Referring to FIG. 4, first conductor portion  561  is shown as a dotted line as it passes through lumen  42  toward first opening  62  and second conductor portion  562  as a solid line residing between the lead body  10  and electrode  12 .  
         [0021]    According to embodiments of the present invention, second conductor portion  562  is press fit in position under the force of the windings of electrode  12 , thus maintaining second conductor portion  562  in electrical contact with one or more of the plurality of windings  68 . Furthermore, according to one embodiment, turns of electrode  12  at one or both ends  701 ,  702  are joined together to help maintain the press fit of second conductor portion  562 ; examples of joining means include but are not limited to welding. Of course, second conductor portion  562  must be free of insulation to effectuate the desired electrical contact, while first conductor portion  561  may have a layer of insulation formed thereover. Electrode  12  is made of any low resistance, corrosion resistant material that is biocompatible and biostable, examples of such materials include platinum/iridium alloys, and second conductor portion  562  residing between lead-body  10  and electrode  12  may be polished as for example by electro-polishing, mechanical polishing, or chemical polishing, to reduce wear due to friction at an interface between second conductor portion  562  and electrode  12 . Second conductor portion  562  may also be coated with a layer of smooth metal (e.g. gold, platinum, etc.). As further illustrated in FIG. 3, according to some embodiments of the present invention, a filler material  70  is deposited between coil turns of electrode  12  and over second conductor portion  562 . Filler material  70  according to some embodiments, is adapted to prevent significant relative motion between electrode  12  and second conductor portion  562  by anchoring second conductor portion  562  and/or electrode to lead body  10 , while, according to alternate embodiments, filler material  70  is adapted to simply encapsulate portions of second conductor portion  562  in order to prevent corrosion of second conductor portion  562 ; in either type of embodiment filler material  70  may be an polymer adhesive, such as a silicone medical adhesive or a polyurethane adhesive, both known to those skilled in the art of lead construction. Furthermore, according to various embodiments, filler material  70  includes a conductive material so that material  70  may be present in between second conductor portion  562  and electrode  12  without significantly impairing electrical coupling between the two. FIG. 3 also illustrates filler material  70  extending into first opening  62  and second opening  64  according to some embodiments of the present invention wherein filler material  70  further serves to seal off lumen  42  and/or anchor second conductor portion  562  to lead body by filling in openings  62 ,  64  around conductor  561 ,  562 ; according to alternate embodiments a separate material from filler material  70  is used to fill in openings  62 ,  64 .  
         [0022]    [0022]FIG. 5A is an axial cross-sectional view of a portion of a lead assembly and FIG. 6 is a plan view of the portion shown in FIG. 5A. As illustrated in FIG. 5A, according to another embodiment of the present invention, first conductor portion  561  extends distally within lumen  42  to a first opening  62  and second conductor portion  562  re-enters lumen  42 , through second opening  64 , and extends proximally, toward proximal end  60  of the lead assembly portion shown. Referring to FIG. 6, first conductor portion  561  is shown as a dotted line as it passes through lumen  42  toward first opening  62  and second conductor portion  562  as a solid line residing between the lead body  10  and electrode  12  and a dashed line within lumen  42  extending back from second opening  64  toward first opening  62 . FIG. 5B is an axial cross-sectional view of a portion of a lead assembly according to yet another embodiment of the present invention wherein first conductor portion  561  extends within lumen  42  toward second opening  64  in proximity to distal end  66  where it exits lumen  42  as second conductor portion  562 , which extends proximally between electrode  12  and lead body  10  to re-enter lumen  42  through first opening  62 . According to the embodiment illustrated in FIG. 5B, routing of second conductor portion from second opening  64 , in proximity to distal end  66 , proximally to first opening  62  may facilitate an assembly of electrode  12  from a distal end of lead body  10  onto lead body  10  over second conductor portion  562  after second conductor portion  562  has been assembled into lead body  10 .  
         [0023]    Although FIGS. 3-5B illustrate embodiments including first and second openings  62 ,  64 , it should be recognized that as illustrated in part in FIG. 1, second conductor portion  562  need not re-enter lead body  10  through a second opening, but may be terminated anywhere beneath electrode  12  according to embodiments of the present invention.  
         [0024]    [0024]FIG. 7 is a radial cross-sectional view illustrating a first alternative configuration of the embodiments shown in FIGS.  5 A-B and FIG. 6. FIG. 7 illustrates a conductor  56  assembled into a lead body  100 , wherein a first portion of conductor  56 , including a layer of insulation  500  formed thereover, resides in lumen  42  and a second portion of conductor  56 , stripped of insulation, resides within a longitudinal channel  110  formed on an exterior surface of lead body  100 . According to some embodiments of the present invention longitudinal channel  110  is preformed into lead-body  100  to accommodated second portion of conductor  56 , however in alternate embodiments, a dedicated channel of this nature is not required since the windings of coil  12  (FIGS. 1-5B) passing over second portion of conductor  56  exert a radially inward force thereon and cause resilient lead-body  100  to become somewhat deformed into, for example, the shape shown in FIG. 7, wherein this resilient force maintains conductor  56  in contact with turns of electrode  12 . FIG. 8 is a radial cross-sectional view illustrating a second alternative configuration of the embodiment shown in FIGS.  5 A-B and FIG. 6. FIG. 8 illustrates a longitudinal opening  115 , as an alternative to channel  110  illustrated in FIG. 7, which accommodates second portion of conductor  56 . According to some embodiments, an adhesive backfill is employed to anchor conductor  56  in channel  115 .  
         [0025]    [0025]FIG. 9 is an axial cross-sectional view of a portion of a lead assembly in accordance with yet another embodiment of the present invention; and FIG. 10 is a plan view of the embodiment shown in FIG. 9. The embodiment illustrated in FIGS. 9 and 10 differs from previously described embodiments in that second conductor portion  562  is wound around lead-body  10  beneath electrode  12  as is shown at  72 . Although first conductor portion  561  is illustrated exiting lumen  42  at first opening  62  and second conductor portion  562  re-entering lumen  42  at second opening  64  where second conductor portion  562  extends distally, alternate embodiments of the present invention include second conductor portion  562  extending proximally upon re-entry into lumen  42  and first conductor portion  561  exiting at second opening  64  and second conductor portion  562  re-entering at first opening  62 . Furthermore, it should be recognized that second conductor portion  562  need not re-enter lead body  10  through a second opening, but may be terminated anywhere beneath electrode  12  according to embodiments of the present invention  
         [0026]    In the foregoing specification, 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. For example, an electrode described herein as a coil may further include a non-coiled portion, for example a solid ring, which may make additional electrical contact with a conductor electrically coupled to the electrode by means of the present invention. Accordingly, the specification and figures are to be regarded as illustrative rather than as restrictive, and all such modifications are intended to be included within the scope of the present invention.