Abstract:
Medical electrical leads including coil electrodes having polymeric material between but not over the coil turns. Some leads can be used for neurological sensing and/or stimulation applications. The coil electrodes are more flexible, bendable, and stretchable relative to corresponding cylindrical band electrodes. The polymer fill between the coil turns provides more column strength than coil electrodes having empty space between the coil turns. Some leads have a lumen for receiving stiffening members while others do not have such lumens. An introducer needle can be used to introduce a steerable sheath containing the lead. The sheath and lead can be advanced to near the target site and the sheath removed. The present invention can be used to advantage in peripheral nerve and other applications. Some leads are made by masking the coil electrode outer surface with heat shrink material and filling the coil inter-strand regions with polymer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from U.S. Provisional Patent Application Ser. No. 60/870,531, filed Dec. 18, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related to implantable electrical medical stimulation and sensing leads. More specifically, the present invention is related to implantable leads with a coil electrode having the coil inter-turn space filled with polymer. 
         [0004]    2. Prior Art 
         [0005]    Implantable electrical leads are well known. Such leads are used in many sensing and stimulation applications. Cardiac leads are used for both sensing and stimulation, for recording, pacing, and defibrillation. Some cardiac leads are used in bi-ventricular pacing for cardiac resynchronization therapy by advancing the lead through the cardiac sinus and into a cardiac vein to pace the left ventricle. Neurological leads have been used for spinal stimulation and for deep brain stimulation (DBS) applications. Other applications include sensing and stimulation for gastric applications. 
         [0006]    Neurological leads often require a larger number of conductors compared to cardiac applications. Some pacing applications only require one or two conductors, while some neurological applications may utilize eight distinct conductors. The leads for many neurological applications require smaller and more flexible leads than for many previous cardiac type applications. In one application, a stimulator is implanted in the front of the abdomen, and a lead or lead extension is tunneled around to the back, under the skin. The lead having multiple distal conductors is often inserted into the epidural space and advanced along the spinal cord, until the multiple electrodes are properly positioned. Such electrodes are typically cylindrical ring electrodes coupled through conductors to ring connector contacts at the proximal end. A small outer diameter and good flexibility is required to achieve the optimal result. 
         [0007]    Peripheral nerve stimulation has become more common, and would often benefit from even smaller lead sizes and greater flexibility. It may be desirable to run leads under the skin along the neck, and along at least part of the head or face. It may also be desirable to run leads under the skin along side joints and other parts of the body that may flex, stretch, and/or rotate. 
         [0008]    Neurological leads often have distal band electrodes having a cylindrical shape. Such band electrodes are typically formed of thin metal bands. Such bands are typically secured on the surface of a polymeric tube, and coupled to thin conductors. The tube often has a lumen, occupied by a stiffening member or stylet during delivery. The stylet can be inserted to provide column strength to allow for pushing the lead through a needle and to the target site. The stylet can then be removed. Without the stylet, the lead is often rather limp, and could not easily be advanced without the added stiffness. Leads implanted under the skin and having distal band electrodes can rub against the skin. Patients having such implanted leads may be acutely aware of any inflexible lead presence over time. 
         [0009]    What would be desirable are implantable leads having smaller outer diameters and more flexible distal regions. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides an implantable medical electrical lead including a flexible elongate tubular body having a proximal region and a distal region, and having a first coil electrode wound around at least a portion of the lead distal region. The coil can include a plurality of coil turns, a distance between the coil turns, and an outer surface to the coil. The first coil can have a polymeric material disposed between the turns, with the first coil outer surface being substantially free of the polymeric material, such that the first coil outer surface is electrically conductive with a surrounding environment. 
         [0011]    In some leads, the tubular body has a lumen disposed through at least part of the lead length. In other leads, the tubular body is substantially solid therethrough and does not have a lumen. Leads may have an outside diameter of less than about 0.050 or 0.035 inch, in various embodiments. Some leads are formed of polyurethane or silicone rubber. Leads often include an elongate conductor extending from the proximal region to the distal region, the first conductor being in electrical continuity with the first coil electrode. 
         [0012]    The present invention also provides methods for making an implantable medical lead. One method includes aligning a plurality of electrically conductive coils along a longitudinal axis, wherein the coils include a plurality of conductor turns, an outer surface, and a space between the conductor turns. The method also includes masking the coils&#39; outer surface with a masking material and infusing a polymer or polymeric precursor material in between the coil turns, but substantially not covering the outer surface of the coils. The polymer or polymeric precursor is allowed to become more solid, such that a polymeric material extends between the coil turns, followed by removing the masking material, such that an electrically conductive coil outer surface is exposed. 
         [0013]    Some embodiments of the present invention also provides methods for pre-loading the polymer or polymeric precursors with limited amount of drugs, such as dexamethasone sodium phosphate, or modifying/grafting the polymer precursors or polymer itself with functional small or large molecules, and infusing the drug-loaded or modified polymer/polymer precursors between the coils&#39; turns. 
         [0014]    In some methods, the coils are disposed over a mandrel during the aligning, the method further comprising removing the mandrel at some point after the solidifying, leaving a lumen though the lead body. In other methods the coils are disposed over a solid polymeric shaft during the aligning, where the solid polymeric shaft is not removed. In still other methods, the coils are disposed over a tubular polymeric shaft having a lumen there through during the aligning, where the tubular polymeric shaft is not removed. 
         [0015]    The masking material is a shrinkable sheath disposed over the coils in some methods, in which the masking includes shrinking the shrinkable sheath. The sheath may be heat shrinkable in some methods. The masking can include urging a mold inner surface against the coils, and/or disposing the coils within a mold. 
         [0016]    The present invention further provides methods for implanting neurological electrical leads. One method includes advancing a hollow delivery needle through the skin, and advancing an electrical lead through the needle, where the lead has a plurality of distal electrodes formed of electrically conductive coils having a substantially electrically conductive outer surface and a substantially filled space in between the coil turns. The advancing can be stopped when the lead is disposed near a target site, followed by withdrawing the delivery needle. In some methods, the lead has a lumen there through, and the method further includes disposing a stiffening member through the lead prior to the advancing, and removing the stiffening member. Some methods include advancing a delivery sheath through the needle, in which at least some of the lead advancing is performed through the advanced delivery sheath and/or advanced together with the advancing delivery sheath at the same time. 
         [0017]    The sheath has a distal region which is steerable in some methods. The lead advancing can include advancing through the spine epidural space, in which sheath distal region is steered to direct the lead toward a nerve root, further comprising advancing the lead to the nerve root. The lead can be advanced toward a peripheral nerve site in some methods. Mapping can be performed in some methods using the lead distal electrodes, through holes or slots in the sheath distal region. Separate mapping electrodes on the sheath distal region may be used in other methods. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a fragmentary, perspective view of a lead according to the present invention having distal coil electrodes and proximal cylindrical ring connector contacts. 
           [0019]      FIG. 2  is fragmentary view of the lead of  FIG. 1 , showing the distal region with coil electrodes and a distal portion of a stylet adapted to slidably fit within the lead to stiffen the lead. 
           [0020]      FIG. 3  is a fragmentary view of the lead of  FIG. 1 , showing the proximal region used to electrically couple to an electrical medical device or a lead extension. 
           [0021]      FIG. 4  is a close up, fragmentary view of the distal region of the lead of  FIG. 1 , showing the coil electrodes and conductors connected to the coils. 
           [0022]      FIG. 5A  is a transverse, cross-sectional view of a lead body having a lumen within for receiving a stiffening member. 
           [0023]      FIG. 5B  is a transverse, cross-sectional view of a lead body not having a lumen within. 
           [0024]      FIGS. 6A ,  6 B and  6 C show one method for introducing the lead of  FIG. 1 , through a steerable sheath introduced through a needle. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]      FIG. 1  illustrates a lead  20  according to the present invention having a distal region  22  and a proximal region  24 . Distal region  22  includes several coil electrodes  26 ,  28 ,  30 , and  32  separated by tubular separating or inter-coil regions  34 . Proximal region  24  includes several connector contacts  38 ,  40 ,  42 , and  44 , separated by tubular separating regions  46 . The connector contacts may be formed of a metal such as Nitinol, MP35N, platinum/iridium, stainless steel, titanium, or other metals typically used in the medical device arts. The connector contacts are typically cylindrical or band shaped, formed of a cylinder of metal wrapped around the lead body, rather than being formed of a coil. Proximal region  24  is often inserted into an electrical medical device, for example, an implantable monitor, or an implantable neurostimulator or the like. Proximal region  24  can also be inserted into a lead extension device to extend the effective length between the lead and the electrical medical device. 
         [0026]    The coil electrodes, such as coil electrode  26 , can be formed of metals, for example, MP35N, platinum/iridium, stainless steel, titanium, and gold, and may have an outer diameter of between about 0.010 inch and 0.050 inch, likely having a size less than about 0.035 inch. The coils have between about 3 and 100 turns per coil in some embodiments, usually at least three turns. In some embodiments, the OD of the coil is less than about 0.035, 0.030, 0.028, 0.025, or 0.020 inches. The lead body can be formed of polyurethane or a silicone rubber in some embodiments. 
         [0027]      FIG. 2  illustrates a prototype of lead  20 , in distal region  22 . Coil electrodes  26 ,  28 ,  30 , and  32  are shown as previously discussed, along with four more coil electrodes all numbered as  33 . Inspection of  FIG. 2  shows that the lead distal region  22  can flex and stretch more than a similar lead having solid band electrodes. Close inspection of inter-coil regions  34  may reveal the multi-strand conductors which run through the lead and are coupled to the coil electrodes. Such conductors typically are individually coupled, one each to a coil electrode, such that the coil electrodes are individually electrically coupled to the proximal end. While not readily visible from  FIG. 2 , the coil electrodes have polymer disposed between the coil turns, but not covering at least a portion of the outer surface of the coils. This makes the coils function as conductive electrodes, while providing some added strength to the lead and inhibiting later in-growth of biological material. 
         [0028]    The distance between each turn is from about 0.0001 inches to about 0.1 inches axially along the longitudinal axis of the lead  20 , and this space is occupied by the polymeric material  36 . The polymeric material  36  also forms the lead outer surface between the respective coil electrodes in the inter-coil regions  34 . 
         [0029]    A stylet  50  is also shown in  FIG. 2 , including a distal end  52 . Stylet  50  can be slidably inserted within a lumen in lead  20 , to stiffen the lead during the lead advance to the target site. As is discussed below, some leads do not require stylets or stylet lumens. 
         [0030]      FIG. 3  illustrates lead  20  proximal region  24 , having connector contacts  38 ,  40 ,  42 , and  44 , as previously discussed, along with four more contacts all numbered  45 . Inter-electrode regions  46  may also be seen. The contacts are typically individually electrically coupled, each to a distal coil electrode. Inspection of  FIG. 3  shows that lead proximal region  24  is not as flexible in going around a tight bend, relative to distal region  22  having the coils. In addition, the solid bands will not stretch as will the coil electrodes. Proximal region  24  may have a port to admit a stylet in some embodiments, while other embodiments have such a stylet entry port in the mid region, while others have no stylet lumen. 
         [0031]      FIG. 4  shows lead distal region  22  in more detail. Multiconductors  35  may be seen extending between the coil electrodes  26 ,  28 , and  30  in inter-coil regions  34 . The coil electrodes are seen to have about 12 turns in this prototype. The conductors can be crimped or welded to the coils in some embodiments, or both coil and conductor may be originally formed of a contiguous electrical conductor in other embodiments. The conductor coupled to each coil may be formed of a single wire for each unique channel in some embodiments and of multi-strand wires in other embodiments. The multi-strand wires may have different configurations in different embodiments, including small diameter coils, which may increase in coil diameter to form the coil electrodes in some embodiments. As previously discussed, the coil turns can have polymer filling the region between the turns, while not covering the outer extent of the coil. Some polymer filling includes a silicone-polyurethane blend. 
         [0032]      FIG. 5A  illustrates one lead in a quasi-transverse cross-section cutting through a distal coil  66 , which has an inner polymer layer  64  having a lumen  62  within. Polymer layer  64  extends from an inner wall  63  to an outer extent  65 , shown in projection behind coil  66 . The conductors may be disposed within polymer layer  64  in some embodiments. A multiconductor wire cable may have the individual conductors arranged side-by-side in a somewhat flattened cable, with the cable itself spirally arranged around the outside of lumen  62 , for example, within polymer layer  64 .  FIG. 5A  actually is a somewhat helically slanted view, through a coil turn, as a strictly transverse slice would show at least some of the polymer between the coil turns, as the coil turn advanced. A helical view through an inter-turn region would likely show polymer where coil  66  is located in  FIG. 5A . This added thickness of polymer may be seen to add to the lead wall thickness and to the column strength of the lead, relative to a lead having empty space between the coil turns. Just as the coil may, in some embodiments, be formed of a single wire strand that coils, the inter-strand region may (absent manufacturing irregularities) be formed of a single strand of polymer that also coils, alternating with the wire strands. 
         [0033]      FIG. 5B  illustrates another lead  70  in a quasi-transverse cross-section through one coil strand  72 . Lead  70  does not have a lumen, but has a solid polymer center  74 , with the polymer extending outward to fill in the inter-strand regions with polymer. The added strength of the polymer filled coils can allow a decrease in lead outer diameter, and even eliminate the need for a stiffening member in some embodiments. 
         [0034]      FIGS. 6A to 6C  show one lead in one example of use. A needle  102  is inserted under skin  100 , and a steerable delivery catheter or sheath  106  advanced through needle  102 . Steerable delivery sheaths are well known in the art. 
         [0035]      FIG. 6B  shows a lead  104  advanced through the sheath  106 . The steerable sheath, either alone, or having a lead within, may be sufficiently strong and stiff to advance through a difficult, even scarred tissue path. A stylet may not be required. A distal mapping electrode  105  may be included on sheath  106  and electrically coupled to a sheath proximal region (not shown in  FIG. 6B ). The mapping electrode may be used to determine the proper location for placing the lead, even before advancing the lead out of the sheath. 
         [0036]      FIG. 6C  illustrates lead  104  after the sheath has been withdrawn, leaving lead  104  in place. 
         [0037]    In some methods, lead  70  may be inserted by itself into a human or mammalian body and advanced to the target site without use of a sheath, introducer, or needle. In some methods, the lead is inserted alone or having only a stiffener. In other methods, an introducer or sheath is used, without a needle. In some coronary methods, the lead may be advanced to the target site (e.g. the coronary sinus or a cardiac vein) using conventional methods used for reaching those target sites. In some coronary applications, the various coils may be individually addressed during surgery or long after surgery, in order to determine the proper coil combination for obtaining the optimal clinical result. In one such example, the various coils may be stimulated one by one or in various combinations to determine the best coil or coils to use for LV pacing from a cardiac vein. 
         [0038]    In some methods, the sheath has its own set of one or more external distal electrodes which can be used in mapping, to locate the optimal site for placement of the lead. In other methods, the sheath has distal holes or slots through the sheath side wall to allow the lead distal electrodes to electrically contact the surrounding tissue. The lead itself can be used for mapping purposes while still disposed in the partially surrounding sheath. 
         [0039]    Devices according to the present invention can be made using various methods. The manufacture of polymeric leads and catheters is well known to those skilled in the art, with millions made each year. The details of the already known aspects of those methods are well documented in the patent literature of the past decades. These details need not be repeated here. Methods for allowing molten polymers to solidify, and for pre-polymers to react and cure (e.g. monomers and catalysts) in place are also well known. 
         [0040]    One lead, having a lumen according to the present invention can be made using various methods. A removable solid mandrel shaft or a removable tube can be used to hold a series of distal coil electrodes, conductors, and proximal connector contacts, in their ultimate position around and along the shaft or tube. A shrink wrap or heat shrink material can be placed over the subassembly and shrunk into place using heat application or other methods. The shrunken material can be used to cover the outer extent of the coils and connector contacts, to mask them from later added polymer. Preferably, the heat shrink material covers an area extending from about 10° to about 180° around the outwardly facing circumference of each coil turn. This is the same area that will eventually be devoid of polymeric material after the heat shrink material is removed. In some methods, the shrink wrap material is either not applied in between the coil electrodes or is applied, then removed prior to the polymer application. 
         [0041]    The device can be placed in a tubular mold, for example, two opposing concave half-tubes which are brought together about the tubular device. A flowable polymeric material can then be infused into the mold to the masked coil electrodes and the remainder of the device. This flowable polymeric material can include a heated thermoplastic material or a pre-polymeric material including monomer. After the polymer has solidified or cured, the mold can be removed. The masking material can be removed to expose the still conductive outer surfaces of the coil electrodes comprising the area extending from about 10° to about 180° around the outwardly facing circumference of each coil turn that was previously covered by the heat shrink material. Most or all of the coil inter-turn regions may be filled with the polymer. The presence of this polymer rather than empty space increases the effective wall thickness and strength of the lead. 
         [0042]    In another method, a lead not having a lumen can be created. The coil electrodes, conductors, and connector contacts may be aligned in a mold without the removable mandrel, and the masking applied, followed by applying pourable polymer or pre-polymer solution. After the polymer has solidified, the device can be removed from the mold. 
         [0043]    In yet another method, the lead can be formed without a lumen but having a non-removable shaft used to provide some stiffness and/or to properly align the coil electrodes. After masking and application of the polymer, the shaft can be left in the lead body. In still another method, a non-removable tube can be used to align the coils, and later be left in place. This tube lumen may or may not later serve as a stylet lumen. 
         [0044]    In some embodiments of the invention, the polymeric material in the coil electrodes may include a medicant formulated by itself or in conjunction with the polymer to elute from the polymer over time. Examples of controlled release formulations, biodegradable polymers, hydrolytically degradable polymers, bioerodable polymers, etc, are well known to those skilled in the art for other uses, such as for coated stents. Some embodiments include one or more steroids in the polymeric material. Some embodiments include glucocorticoid type steroids, for example dexamethasone (the formal name of which is believed to be 9-fluoro-11β,17,21-trihydroxy-16a-methylpregna-1,4-diene-3,20-dione). Such a steroid eluting lead may be particularly beneficial for leads placed in a cardiac vein for LV pacing and/or sensing applications. 
         [0045]    Various examples of various embodiments have been described to illustrate some aspects of the invention. The scope of the invention is given in the claims which follow.