Abstract:
Devices and methods for stimulating nerves, such as peripheral nerves are described. Some devices can include small cross-section lead bodies having one or more electrodes in the round distal portion, the electrodes having a substantially planar surface within the distal portion of the lead which is suitable for placement through a cylindrical needle intended to access a spinal region of a patient. Some lead electrodes are covered with a hydrophilic coating at least about 0.001 inches thick. The hydrophilic coating may include a steroid and/or a GABA (gamma-aminobutyric acid) agonist which can elute or diffuse over time, away from the electrode.

Description:
RELATED APPLICATIONS 
     The present application is a nonprovisional of U.S. Provisional Patent Application No. 60/782,819, filed Mar. 16, 2006, titled HIGH EFFICIENCY NEUROSTIMULATION LEAD. 
     TECHNICAL FIELD 
     The present invention is related generally to medical devices. More specifically the present invention is related to neurostimulation leads. 
     BACKGROUND 
     Implantable leads, typically having externally exposed ring or band electrodes can be used to deliver electrical stimulation to surrounding tissue and/or to sense electrical energy produced by the surrounding tissue. Such leads are often implanted, for example, within the epidural or intrathecal spaces of the spinal column, along peripheral nerves, within the brain, and about the heart. Electrical stimulation of the spinal cord has been shown to be effective in relieving intractable pain in some patients. Such electrical stimulation can reduce or eliminate the use of pain relieving drugs. Examples of some leads may be found in U.S. Pat. Nos. 6,721,604; 6,981,314; 6,216,045; and 5,483,022, herein incorporated by reference. 
     One such lead is formed of polymeric material, for example, polyurethane or silicone. The lead can be nominally  1  mm in outer diameter and about 20 cm in length. A typical lead may have a series of electrodes formed as bands or rings disposed in a spaced apart relationship in a lead distal region. The distal region of the lead can be introduced, for example, into the epidural region for use in stimulation of the spinal column. The lead proximal region may have a corresponding set of band or ring connectors or terminals, one for each corresponding electrode in the distal region. Each proximal region terminal can thus be connected to one distal electrode in a typical configuration. 
     The terminals can be used to couple the proximal end of the lead to a lead extension, which can in turn be coupled to an implantable pulse generator (IPG). The lead extension can provide added length to extend the reach of the lead to a more distantly placed IPG. In some embodiments, the lead extension is between about 20 and 50 cm in length. 
     The lead typically has a lumen extending from the proximal end through to the distal region, with the lumen being dimensioned to accept a stiffening member or stylet. The lead, commonly formed of a polymeric material and being very small in cross section, is typically very floppy and not pushable. With a stylet or stiffening member inserted, the lead gains the needed pushability, and can be advanced into and up the spinal column to the desired location. 
     Current neurostimulation leads often use polished platinum electrodes having relatively large surface areas. Leads are described in U.S. Pat. Nos. 5,103,837; 5,324,324; 5,345,933; 4,044,774; and 5,265,608, herein incorporated by reference. Typical percutaneously inserted leads can use ring electrodes that wrap around 360 degrees. This is often wasteful, as energy is delivered to tissue that is not intended to be stimulated. Such wasted energy may lead to shortened battery life. This can also lead to side effects such as pain in those tissues. 
     What would be desirable are leads that can be percutaneously inserted and provide directional stimulation. 
     SUMMARY 
     Some embodiments of the present invention include the use of directional electrodes that can be percutaneously delivered. In some embodiments, the lead has a flat face at the distal end that predominately or only stimulates in one direction. Optionally, the electrodes can be coated with a hydrophilic polymer film, layer, or coating. The polymer absorbs body fluid, which allows the electrical charge to pass through the polymer from the metal substrate to the stimulatable tissue. This minimizes polarization of the electrodes. It may also present a more biocompatible surface to the tissue, minimizing the foreign body response to the implanted electrode. 
     Minimizing the response may limit the amount of fibrosis, or scar tissue that forms at the electrode surface. This type of tissue essentially acts as an insulator and increases the energy requirements of the system. Additionally, pharmaceutical agents can be included in the polymer. These agents can elute out of the polymer matrix over time and modify the tissue response to the lead. Pharmaceuticals agents in some embodiments may include steroids, for example, beclamethasone, dexamethosone, etc and their derivatives. These agents minimize the inflammatory response to the implanted foreign body. 
     A different class of drug that can be included in some embodiments are GABA (gamma-aminobutyric acid) agonists, for example, baclofen. These drugs enhance the ability of the stimulation to generate action potentials in the target nerves. 
     The present invention provides an implantable medical electrical lead including, an elongate body having a proximal portion, a distal portion, and at least one electrical conductor extending between the proximal portion and the distal portion: and a first electrode disposed in the distal portion, the first electrode having a substantially flat, planar surface and being electrically coupled to the conductor. The lead elongate body and electrode may be sized small enough in cross-sectional profile to be insertable through a 12 gauge needle. Some leads also include a hydrophilic coating over the flat electrode surface, the coating having a thickness of at least about 0.001 inch or 0.0005 inch, or between about 0.0001 and 0.01 inch, in various embodiments. The hydrophilic coating is swellable in water, in some embodiments. Some coatings include a steroid substance disposed within the hydrophilic coating for diffusion out of the hydrophilic coating. In some embodiments, the steroid is selected from the group consisting of beclamethason, dexamethosone, and their derivatives, and combinations thereof. 
     Some embodiment leads include a GABA agonist substance disposed within the hydrophilic coating for diffusion out of the hydrophilic coating, for example, baclofen. 
     The present invention also provides a method for implanting a medical electrical lead, the method including advancing an implantable medical electrical lead through a needle smaller than about 12 gauge to a target site. The lead can include an elongate body having a proximal portion, a distal portion, and at least one electrical conductor extending between the proximal portion and the distal portion. The lead may also include a first electrode disposed in the distal portion, the first electrode having a substantially flat, planar surface and being electrically coupled to the at least one conductor, where the lead elongate body and electrode are sized small enough in cross-sectional profile to be insertable through a 12 gauge needle. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a fragmentary, perspective view of a lead distal region in one embodiment, having substantially planar, nominally square shaped electrodes. 
         FIG. 2  is a fragmentary, front view of a lead distal region in one embodiment, having substantially planar, nominally rectangular electrodes. 
         FIG. 3  is a fragmentary, side, cross-sectional view of the lead distal region of  FIG. 2 , having a polymeric, hydrophilic layer over the electrode metal surface. 
         FIG. 4  is a perspective view of one electrode of  FIG. 3 , having the polymeric hydrophilic layer disposed over the metallic electrode surface. 
         FIG. 5  is a fragmentary, bottom view of a lead according to the present invention having a distal region with four electrodes and a proximal region with four conductor rings. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides leads, sized in some embodiments such that it can be delivered via a percutaneously placed needle, for example, smaller than 12 gauge, typically between 13 and 28 gauge. The lead distal end or distal portion can have at least one flat face. Electrodes may be disposed on at least one of the flat faces and can have a flat surface in some embodiments of the invention. The electrode metal substrate can be a corrosion resistant, biocompatible and biostable material, such as platinum, platinum alloys, titanium or titanium alloy, gold, etc. 
     The lead can have 1 or more electrodes (preferably 1-32 and more preferably 4-8 electrodes), with electrical conductors connecting the distal and proximal regions and/or ends, with the proximal region and/or end containing the corresponding number of contacts and configured to be compatible to an implanted pulse generator, or other power source. The electrode dimensions are optimized for battery life by minimizing current loss into undesirable tissue. 
     The insulation of the lead body, and distal and proximal ends, can be a biocompatible and biostable polymer, such as polyurethane, silicone, polyurethane-silicone hybrid, PEEK™, polyimide, etc. 
       FIG. 1  shows one lead  20  according to the present invention, having a polymeric distal region  24  including a housing  40  having four flat surface planar electrodes  30 ,  32 ,  34 , and  36  disposed within a substantially flat housing region  28 . Electrical conductors  42  may be seen in a cutout view extending proximally. Lead  20  terminates in this embodiment in a somewhat rounded distal end  26 . 
       FIG. 2  illustrates another lead embodiment  120  having a width of less than 2 mm, here about 1.3 mm, indicated at  144 , and having electrodes  130 ,  132 , and  134  with a surface area of less than about 3 square mm, here about 2 square mm. Lead  120  terminates in a distal tip  126 . 
       FIG. 3  illustrates lead  120  of  FIG. 2  in cross section, having a thickness of less than about 1 mm, here about 0.75 mm, indicated at  146 . Housing  148  houses a first electrode  130  having a conductor layer and a surface coating or layer  152 &gt;which can include a hydrophilic material, steroid, and/or a GABA agonist. A second electrode  132  having a conductor layer  154  with a coating  156  is also shown. 
       FIG. 4  illustrates lead electrode  133 , having a flat metal substrate  150  coated with a hydrophilic layer  152 . 
       FIG. 5  illustrates a neurological stimulation lead  220  according to the present invention. Lead  220  can incorporate a multiconductor cable. Lead  220  has a distal region  224  a proximal region  226  and an intermediate region  228  disposed between the distal and proximal regions. In a preferred embodiment, the intermediate region is defined to lie between the innermost distal and proximal electrical contacts described below. Lead  220  can be formed of a body or shaft  234  extending between a distal end  230  and a proximal end  232 . Lead body  234  has an exterior surface or side wall  236 . In some embodiments, the lead body proximal of the distal region has a substantially round cross section, while in other embodiments the lead regions proximal of the distal region are flat on at least one side, similar to the shape of the distal region bearing the electrodes. Lead body  234  is preferably formed of a polymeric material, for example, polyurethane or silicone. 
     Lead distal region  224  may include a number of electrodes  238 , which may, for example, be cathodes disposed along the bottom of lead body  234  in a spaced-apart configuration. Electrodes  238  may also be described as electrical contacts. Electrodes  238  are normally adapted to be inserted into the human body, are externally exposed, and can be used for neurological stimulation. One exemplary use of electrodes  238  is the stimulation of the nerves within the spinal cord. Proximal region  226  can include a number of connector bands or connector rings  240  disposed in a spaced-apart configuration. Connectors  240  may also be described as electrical contacts or terminals, and are preferably also externally exposed. Connectors may be circumferential or flat, and may be made from platinum, platinum alloys, stainless steel, nickel alloys, etc. Electrodes  238  and connectors  240  may be formed of Platinum and/or Iridium. Connectors  240  can be used for connecting lead  220  to a lead extension to extend the effective length of the lead. In some uses, connectors  240  may also be used to directly couple lead  220  to an implantable pulse generator. 
     Electrodes  238  and connectors  240  can be coupled to each other in a one-to-one arrangement. In some leads, the distal-most electrode is coupled to the distal-most connector, the second-to-distal-most electrode coupled to the second-to-distal-most connector, and so forth. The electrodes and connectors can be coupled through conductors extending between the two. In some leads, the conductors are embedded within the lead while in other leads, the conductors lie within lumens extending the length of the lead. In some leads, the conductors are disposed within lumens that are later backfilled to substantially fill the lumens with a polymeric material. Some leads have stylet lumens for receiving a stiffening stylet member. 
     Lead  220  can be varied in outer diameter and length to suit the application for which it is intended. In some embodiments, lead  220  has a total length of between about 5 cm and about 100 cm. In other embodiments, lead  220  has an outer diameter of less than about 1 mm and a total length of between about 10 cm and 150 cm. 
     Uses for the present invention include, but are not limited to: spinal cord stimulation; brain stimulation; any central nervous system stimulation; any peripheral nerve stimulation; including but not limited to occipital, orbital, cranial, sacral, pudendal, vagus, and/or radial nerves, cardiac pacing and/or defibrillation; smooth muscle stimulation (stomach, liver, etc); and skeletal muscle stimulation. 
     Leads according to the present invention can be introduced into the epidural space and used to stimulate the spinal cord. In another use, a lead can be introduced into the intrathecal space for spinal cord stimulation. While not wishing to be bound by theory, applicants believe that intrathecal stimulation is not currently used because circumferential electrodes would dump too much current into the highly conductive cerebral spinal fluid. Highly directional electrodes of some embodiments of the present invention, placed in close proximity to the spinal cord, may require much lower current. In some embodiment methods, a GABA agonist coating or layer on the lead distal region: for example, on the electrode, can be placed much closer to the spinal cord when the lead is placed in the intrathecal space. This close proximity to the nerves may increase the effectiveness of the GABA agonist. The GABA agonist coating or coating may also be used in peripheral nerve stimulation. Applicants believe peripheral nerve stimulation may also benefit from the close proximity of the electrode and drug to the nerve. 
     Various examples and embodiments of the present invention have been presented above, and are intended to illustrate some aspects of the present invention. The scope of the present invention is to be defined by the claims which follow.