Abstract:
A temporary medical lead in which stimulating electrical energy is transmitted to body tissue through the lead electrodes via ionic conduction within the hydrogel material. The structure of the hydrophilic hydrogel material consists of a porous structure into which conductive salt ions are diffused. In addition the structure of the hydrogel material can be loaded with a single or combination of therapeutic drugs from which is eluted from the electrode&#39;s surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from U.S. Provisional Application Ser. No. 61/218,498, filed Jun. 19, 2009. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention is related generally to medical stimulation leads. More specifically, the present invention is related to a temporary stimulation lead with polymer electrodes. 
         [0004]    2. Background Art 
         [0005]    Medical stimulation leads provide a means to deliver electrical energy from an implantable medical device such as a pacemaker or neurostimulator to stimulate body tissue. Such leads are complex devices that are designed with an intricate network of conductor wires and electrodes. Medical stimulation leads can be categorized as being either a permanent medical lead or a temporary medical lead. As the name implies, permanent medical stimulation leads are placed in the body for chronic use to provide continuous long-term stimulation to cardiac or neurological tissue. On the other hand, a temporary medical stimulation lead is designed for relatively short term use in the body. Permanent medical stimulation leads are designed for long term implantation of about 6 months or more and are typically constructed with more durability than temporary medical stimulation leads. 
         [0006]    Before a permanent medical lead system is implanted, a temporary stimulation lead is used to screen potential patients for therapy effectiveness. This saves expense and minimizes the invasiveness of the procedure to the patient until it can be proven that the system will be efficacious. Previous prior art temporary leads provide monopolar stimulation in an effort to save size and expense. The present invention provides a cost effective multi-polar temporary lead with a small diameter which creates less trauma to the patient. 
         [0007]    Polymeric materials have previously been used to construct medical stimulation leads. Such leads utilizing polymeric materials are disclosed in U.S. Pat. No. 7,225,035 to Brabec et al., U.S. Pat. No. 6,922,588 to Kranz et al. and U.S. Pat. No. 5,667,615 to Maurer et al. 
         [0008]    Brabec et al. in the &#39;035 patent discloses the use of conductive polymers such as carbon filled silicone, polyacetylene, polypyrrole and polyanaline for use as an electrode material. Such materials, as stated by Brabec, provide flexibility and allow the electrode to bend in the tight spaces of the coronary vasculature. 
         [0009]    Kranz et al. in the &#39;588 patent discloses the use of conductive polymeric materials that have been specially processed to produce an anisotropic electrical behavior. In the 588 patent, conductive polymeric materials such as polyacetylene, polyparaphenylene, polyphenylene sulfide, polyparaphenylvinylene, polypyrrole, polyfuran, polythiophen, polyphenylamine, polyethylenedioxythiophen-polystyrene sulfonate and polyacene, are processed to produce an electrically conductive medical lead (electrode line as stated by Kranz) designed to minimize electrical radial conduction and enhance electrical conduction along the lead&#39;s longitudinal axis. As Kranz states, in column 4, line 32 of the &#39;588 patent, “By presetting the respective polymerisation and processing conditions which are to be adapted to the respective individual case involved, it is possible to ensure that the individual polymer chains of the intrinsically conductive polymer coaxially oriented in the longitudinal direction of the electrode line  12  and there is no conductivity worth mentioning in the radial direction.” As will be discussed in more detail, the present invention is directed to the use of polymeric materials in electrodes where emission of electrical energy in a radial direction is desired. 
         [0010]    Mauerer et al. in the &#39;615 patent is directed to a vaginal electrode with alternating bands of conductive carbon filled silicone and non-conductive silicone rubber. Mauerer discloses an improved means of coupling electrical energy to the electrode through the use of mechanical tension to secure the lead wires to the polymeric electrodes of carbon loaded silicon rubber. 
         [0011]    Unlike Mauerer, however, the temporary medical stimulation lead of the present invention utilizes a hydrophilic polymeric hydrogel material that acts as both an electrical stimulation electrode and a reservoir from which a therapeutic drug is eluted. Electrical energy is radially emitted from the hydrogel structure that provides therapeutic electrical stimulation to body tissue. In addition, a therapeutic drug can be emitted from the surface of the hydrophilic hydrogel material from which it is stored. 
         [0012]    Furthermore, the present invention provides multipolar stimulation that provides increased control of the electrical stimulation as compared to monopolar prior art stimulation. In addition to the medical lead&#39;s simplified construction, the use of the conductive hydrophilic hydrogel material provides a cost effective means to stimulate tissue and elute therapeutic drugs that provide a pharmacological benefit. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention comprises a medical device lead that utilizes a polymeric hydrophilic hydrogel material as the electrode structure of a temporary medical lead. The hydrophilic hydrogel electrode operates on the principal of ionic conduction. Salt ions that are diffused into the porous hydrophilic hydrogel structure act as electrical conductors that transfer electrical energy from the medical device to targeted body tissue. The hydrogel material also acts as a vehicle capable of eluting a therapeutic drug. The present invention comprises an elongated lead body having proximal and distal lead regions through which conductor wires extend through the lead body center from the proximal region to the distal region. 
         [0014]    A series of individually insulated conductor wires contained within the implantable medical device extend the length thereof from the lead&#39;s proximal region to the distal region of the lead. The strands of conductor wires are bundled in a cable or coiled form for ease of manufacture. 
         [0015]    The distal region of the lead is comprised of a series of alternating bands of electrically conductive and insulating polymers. The alternating conductive and insulating polymer bands comprising the lead&#39;s distal region wrap around the bundle of conductor wire strands. These alternating conduction and insulation polymer bands create a series of electrically isolated electrodes through which the medical device&#39;s electrical energy is transmitted to the targeted tissue. Each strand of conductor wire is electrically connected to a single hydrogel conduction band i.e., an electrode. The lead is designed to allow for the emission of positively and negatively charged electrical energy creating a multipolar lead in which electrical energy delivered through the hydrogel electrode is independently controlled by the medical device. 
         [0016]    The conductive polymer bands are made from a hydrophilic hydrogel polymeric material that has been diffused with electrically conductive salt ions. These salt ions enable the flow of electrical energy via the migration of conductive ions within the material, thus creating an electrode in which electricity is conductable through the hydrogel material and radially emittable from the electrode surface for stimulating tissue that is in contact with the hydrogel electrode. 
         [0017]    The insulation bands located on both sides of the conduction band serve to electrically isolate the hydrogel electrode bands of the present invention. In addition to preventing electrical shorting, the isolation bands enable the electrodes to operate and deliver electrical energy that is of an independent magnitude and polarity from each other. 
         [0018]    The structure of the hydrophilic hydrogel material can also be loaded with a therapeutic drug that is eluted from the electrode surface providing a pharmacological treatment. 
         [0019]    Therefore, the present invention is a temporary medical stimulation lead with electrodes made from a hydrophilic hydrogel material that provides both electrical stimulation and pharmacological treatment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a perspective view of the present invention of a temporary medical lead system. 
           [0021]      FIG. 2  shows an enlarged perspective view of the distal region of the present medical lead. 
           [0022]      FIG. 3  illustrates an enlarged cross-sectional view taken along line  3 - 3  of  FIG. 2  of the present invention depicting the notched conductor wire in the hydrogel electrode band. 
           [0023]      FIG. 4  depicts a cross sectional view taken along line  4 - 4  illustrating the notch in the insulation of the conductor wire strand in the electrode band. 
           [0024]      FIG. 5  illustrates an enlarged cross-sectional view taken along line  5 - 5  of  FIG. 2  of the present invention depicting a severed conductor wire strand in the insulation band. 
           [0025]      FIG. 6  depicts a perspective view of the present invention with a coiled conductor wire embodiment. 
           [0026]      FIG. 7  illustrates an enlarged cross-sectional view taken along line  7 - 7  of  FIG. 6  of the present invention depicting a notched wire strand of the coiled conductor wire embodiment in the hydrogel electrode band. 
           [0027]      FIG. 8  illustrates an enlarged cross-sectional view taken along line  8 - 8  of  FIG. 6  of the present invention depicting a gap of space in an insulation band between a severed wire strand of the coiled wire embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Now referring to the figures,  FIG. 1  shows a perspective view of the present invention of a medical lead  10  that is intended for temporary implantation in a patient. The lead of the present invention is designed to provide, if desired, both electrical stimulation and pharmacological treatment to cardiac, neurological or other targeted tissue. 
         [0029]    The medical lead  10  comprises a flexible, elongated lead body  12  having a thickness and a length comprising a lead proximal region  14  and a lead distal region  16 . As shown in  FIG. 2 , a longitudinal axis A-A extends along the lead body  12 . In a preferred embodiment, the lead body  12  has a diameter that ranges from about 1 mm to about 6 mm and a length that ranges from about 15 cm to about 200 cm. A plurality of individual electrically insulated conductor wires  18  reside in the lead body  12 . The conductor wires  18  extend from the lead proximal region  14  to the lead distal region  16  along the longitudinal axis A-A. The portion of the conductor wires  18  located at the lead proximal end  20  are connectable to a medical device  22  such as the one shown in  FIG. 1 . 
         [0030]    In a preferred embodiment, there are a total of sixteen insulated conductor wires  18 , each made from a wire strand  24  of a preferred metallic material such as MP35N, titanium, stainless steel or silver cored wire. Surrounding each wire strand  24  is an electrically insulative coating  26 , preferably made of polyurethane, polyimide, silicone, polytetrafluoroethylene, ethylene tetrafluoroethylene, fluoropolymers and combinations thereof. The insulative coating  26  preferably extends along the entire length of each of the wire strands  24 . Alternately, these insulated conductor wires  18  could be made from a conductive polymer such as polypyrrole or carbon filled silicone. Although it is preferred that the lead body  12  contain sixteen insulated conductor wires  18 , the present invention could be made with more or a fewer number of insulated conductor wires  18 . 
         [0031]    Within the lead distal region  16  are a series of alternating insulation bands  28  and conduction bands  30 , as shown in  FIGS. 1 ,  2 , and  6 . Both the insulation bands  28  and conduction bands  30  are discrete bands with a length and thickness that reside along longitudinal axis A-A, in which the insulated conductor wires  18  pass through. In a preferred embodiment, the insulation bands  28  have a solid insulation body  32  and the conductor bands  30  have a solid conductor body  34  through which the insulated conductor wires  18  tunnel therethrough. As shown in the cross sectional view in  FIG. 4 , four insulated conductor wires  18 A,  18 B,  18 C and  18 D extend along the length of the conductor band  30 A. Conductor band body  34 A surrounds insulated conductor wires  18 A,  18 B,  18 C and  18 D. Alternatively, both the insulation bands  28  and conductor bands  30  can be constructed with a hollow passageway that allows space for the insulated conductor wires  18 . 
         [0032]    In a preferred embodiment, the insulation bands  28  have a preferred diameter of about 1.5 mm, a length of about 1 cm to about 10 cm and a thickness therewithin. It is preferred that the conduction bands  28  have a diameter of about 3 mm, a length of about 1 cm to about 10 cm and a thickness therewithin. However, the diameter of both the insulation and conductive bands can range from about 1 mm to about 6 mm. 
         [0033]    Also shown in  FIG. 1  is an anchor structure  36  comprised of two protruding prongs  38 A,  38 B. The anchor structure  36  is designed so that the medical lead  10  can be easily advanced distally into position, but proximal movement is restricted due to the protruding prongs  38 A, 38 B. Prongs  38 A, 38 B are composed of a biocompatible insulative polymer such as silicone rubber or polyurethane that provide a rigid yet flexible structure. The prongs  38 A, 38 B are attached to the exterior of the lead body  12  at the proximal end of the lead distal region  16  in such a manner that each prong  38 A, 38 B is oriented at an angle of about 20 to about 40 degrees from longitudinal axis A-A with their terminal ends pointed outwardly toward the lead proximal region  14 . The prongs  38 A,  38 B of the anchor structure  36  flex downwardly toward the lead body  12 . Each of the prongs  38 A, 38 B are curved with a concave backside that matches the curved contour of the lead body  12 . 
         [0034]      FIG. 2  illustrates an enlarged view of the lead distal region  16 . The lead distal region  16  comprises of a series of alternating insulation bands  28 A,  28 B,  28 C,  28 D and  28 E and conduction bands  30 A,  30 B,  30 C and  30 D, which act as the electrodes of the lead. Extending through the center of these bands  28 , 30  are a plurality of individually insulated conductor wires  18 . In a preferred embodiment, there is one more insulation band  28  than conduction band  30 , and the number of conduction bands  30  equals the number of insulated conductor wires  18 . For example, it is preferred that there are sixteen conductor wires  18  and sixteen conduction bands  30 , each conductor wire  18  being in electrical contact with the hydrogel material of a respective conductor band  30 . Although it is preferred that the number of insulation wires  18  equals the number of conductor bands  30 , it is contemplated that multiple insulation wires  18  could be electrically connected to a single conduction band  30  to provide redundancy and a more robust medical lead  10 . 
         [0035]    In a preferred embodiment, conduction bands  30 , including the conductor band body  34 , are composed of an electrically conductive hydrophilic hydrogel polymer such as a thermoplastic polyurethane elastomer which is sold under the trade name of Techophilic and manufactured by Lubrizol Advanced Materials of Wickliffe, Ohio. 
         [0036]    The hydrophilic hydrogel polymer is designed to absorb a liquid such as a saline solution. Salt ions from the saline solution incorporate into the porous hydrogel material structure to provide a means for electrical conduction within the hydrogel material of the conductor band. Prior to use, the medical lead  10  is submerged in saline where it is allowed to soak for about 10 minutes to about 3 hours. That is so the conduction bands  30  have a sufficient amount of saline and electrically conductive salt ions diffused in the hydrophilic polymer hydrogel structure. 
         [0037]    It is possible, however, that the medical lead  10  could be inserted into the body without previously soaking the lead in saline. In this situation, the operation of the medical lead  10  would rely upon the diffusion of ions present in the body into the hydrogel material to provide electrical conductivity. 
         [0038]    In addition, a therapeutic drug can be loaded within the porous hydrophilic structure of the hydrogel material. Prior to insertion of the lead into a body tissue, the therapeutic drug is incorporated into the structure of the hydrogel by either soaking the hydrogel material in the therapeutic drug or injecting the hydrogel material with the therapeutic drug, such as with a needle or syringe. The therapeutic drug is then sequentially eluted from the porous structure of the hydrogel material when the conduction band  30  is located at a targeted site. This elution of a therapeutic drug provides a pharmacologic benefit in addition to providing electrical stimulation. Therapeutic drugs are eluted from the hydrogel material of the conductor band  30  to prevent and combat infection, and control pain among other therapeutic benefits. Suitable therapeutic drugs include, but are not limited to, beclamethason, baclofen, dexamethosone, coumadin, heparin, their derivatives and the like. 
         [0039]    In a preferred embodiment, the insulation bands  28  are made from a biocompatible electrically insulative material such as polyurethane, polyimide, silicone, polytetrafluoroethylene, Ethylene tetrafluoroethylene, fluoropolymers and combinations thereof. 
         [0040]      FIG. 3  is an enlarged cross-sectional view of conductor band  30 A. As shown in the figure, the insulation on the conductor wire  18 A is notched  40 , thus revealing a portion of bare conductor wire  24 A. The amount of removed insulation  26 A could be a relatively small spot or it could have sufficient length in the shape of a band. 
         [0041]    Exposing the bare conductor wire  24 A to the hydrogel material creates an electrical connection between the wire  24  and conductor  30 . There is one notched insulated conductor wire  18  per corresponding conductor band  30 . By limiting the conductor band  30  to one corresponding notched insulated conductor wire  18 , a multichannel electrode medical lead is created in which each conductor band  30  (i.e. electrode) is independently controllable by the medical device  22 . Each conductor band  30  is electrically connected to a single insulated conductor wire  18  and establishes an independently controllable electrical channel between the medical device  22  and conductor band  30 , i.e. electrode. 
         [0042]    For example, the present invention may be configured in which a first conductor band  30 A is connected to a first insulated conductor wire  18 A via a notch  40  in the insulation  26 A of the first wire  24 A, thereby creating a first channel, a second electrode band  30 B is connected to a second insulated conductor wire  18 B via a notch  40  in the insulation  26 B of the second wire  24 B, thereby creating a second channel, and so forth until all the conductor bands  30  are connected to insulated conductor wires  18  via at least one notch  40  in the insulation  26  of a respective conductor wire  24 , thereby creating independent channels. Therefore, the medical device  22  is capable of independently controlling the amount of electrical energy being transmitted to each independent conductor band  30 . 
         [0043]    Although the lead may be produced with any number of electrode channels, it is preferred that the lead have an even number of electrode channels to allow for a balance of positive and negative electrical charges. The multiple independent channels of the device make it possible for the lead of the present invention to be multi-polar. A multi-polar lead is one in which both positive and negative electrical energy is conducted and emitted through the conductor bands  30 , i.e. electrodes of the medical lead  22 . 
         [0044]    The insulated conductor wires  18  are electrically terminated within the insulation bands  28 . After the insulated conductor wire  18  has been notched  40 , exposing the bare wire  24  and therefore creating an electrical connection to the conductor band  30 , it is preferably cut or severed the wire at the next adjacent distal insulation band  28 . In other words, a conductor wire  18  is preferably terminated in the next insulation band  28  that is distal to the conductor band  30  radially aligned with the notch  40  in that particular wire  18 . This construction is primarily one of ease of manufacturability. Instead of constructing the lead from conductor wires  18  of different lengths corresponding to the axial position of their respective conductor bands  30 , all of the wires forming the cable or coil, and the like, are of the same length. Then, each wire  24  has its insulation  26  notched  40  in alignment with its conductor band  30  and cut in alignment with the next distal most insulation band  28 . The severed distal portions of each wire  24  are left in the lead even though they are no longer electrically connected to anything. This facilitates ease of manufacturability. 
         [0045]    Alternatively, the insulated conductor wire  18  can be terminated by ending the insulated conductor wire  18  in the distal insulation band  28 . 
         [0046]      FIG. 4  shows a cross sectional view, taken along line  4 - 4  of the conductor band  30 A. As the figure shows, a series of four insulated conductor wires  18 A,  18 B,  18 C and  18 D are encased in the hydrogel material which comprises the conductor body  34 A. Each of the conductor wires  24 A,  24 B,  24 C and  24 D has a sheat-of insulation material  26 A,  26 B,  26 C and  26 D surrounding the diameter of the wire  24 . 
         [0047]    As shown in  FIG. 5 , in a preferred embodiment, there is a gap  42  in which the insulated conductor wire  18 A is severed in two distinct wire halves in an insulation band  28 B. A laser is preferably used to ablate and sever the wire  18 . The insulated conductor wires  18  are terminated to prevent electrical shorting at the lead distal end  44 . 
         [0048]    As shown in  FIG. 6 , in an alternate embodiment, insulated conductor wires  18  can be bundled in the form of a coil. As previously shown in  FIG. 3  in which the insulated conductor wires  18  are bundled in the form of a cable, each of the coiled conductor wires  46  in the alternate embodiment form has a coiled conductor notch  48 . The coiled conductor wires  46  are terminated in the insulation bands  28 . It should be noted that the insulated conductor wires  18  in the present invention are not limited to bundling in the form of a coil or cable but could also be bundled in other forms such as a braid or as a insulated straight conductor wire  18 . 
         [0049]      FIG. 7  illustrates an enlarged cross-sectional view taken along line  7 - 7  of  FIG. 6 . This drawing shows a notch  48 A in the insulation coating  26  of the coiled wire embodiment  46  of the present invention. Similarly to the cable embodiment, shown in  FIG. 3 , a section of insulation coating  26  is removed from the coiled conductor wire  46 , exposing an area of bare conductor wire  24 . This exposed coiled conductor wire  24  forms an electrical connection path to the conductive hydrogel material of the conduction band  30 A. 
         [0050]      FIG. 8  illustrates an enlarged cross-sectional view taken along line  8 - 8  of  FIG. 6 . This drawing shows a gap  50  between two portions of a coiled conductor wire  46 . Similar to the cable embodiment shown in  FIG. 5 , in a preferred embodiment, a coiled conductor wire  46  is electrically terminated by severing the wire  46  in two. As in the cabled wire embodiment, each coiled conductor wire  46  is electrically terminated in the insulation band  28 . Once the insulation of the coiled conductor wire  46  is notched  48 , exposing the bare coiled conductor wire it is them electrically terminated in the next distal insulation band  28 . 
         [0051]    In a preferred embodiment, the medical device lead  10  is constructed by first twisting the insulated conductor wires  18  in a cable or coiled form. The number of individual insulated conductor wires  18  corresponds to the number of conductor bands  30 , i.e., electrodes. For example, four insulated conductor wires  18  correspond to four conductor bands  30 , i.e. electrodes, eight insulated conductor wires  18  correspond to eight conductor bands  30 , i.e. electrodes, and so forth. 
         [0052]    Second, the wire insulation material  26  is removed from the conductor wires  18 . Preferably a laser is used to ablate the insulate to create a bare, uninsulate spot on the conductor wire  18 . Third, alternating tubes of the polymeric hydrogel conductor tubing and polymeric insulation tubing are placed over the insulated conductor wires  18 , whether in a cabled or coiled form. 
         [0053]    As previously mentioned, these insulation and conductor tubes can either be solid or hollow. When solid tubes are used, the insulated conductive wires  18  are bored through the material. When using coiled conductor wires  46 , it is preferred that a mandrel be placed through the center of the coil. Tubes to provide added stiffness and act as a stylet can also be located in the center of the coil. 
         [0054]    In a preferred embodiment, tubes of the polymeric insulation material are placed before and after the conductive tubes to provide electrical insulation and create electrically isolated conductor bands  30 . 
         [0055]    Third, heat shrink tubing is placed over the assembly and heat treated at about 200° C. to about 300° C. for about 30 to about 300 minutes. This heat treatment fuses the assembly of insulated conductor wires  18 , and conductor and insulation tubes together, thereby creating intimate contact between the various areas of bare conductor wire  24  and conduction band material. Heat treatment also seals the alternating conductive and insulation tube segments together. Therefore, the alternating series of insulation bands  28  and conductor bands  30  are created. 
         [0056]    Prior to use, the medical lead  10  is soaked in a bath of saline to transfer salt ions of the saline solution into the hydrogel structure of the conductor bands  30 . It is preferred that the medical lead  10  be soaked in the saline bath for about 10 minutes to about 60 minutes. Additionally, the conductor bands  30  of the medical lead  10  can be soaked in or injected with a single therapeutic drug or combination of therapeutic drugs. 
         [0057]    In that manner, the present medical stimulation lead is provided. The lead is capable of providing electrical stimulation and or pharmacological treatment when used in conjunction with a medical procedure intended to beneficially affect a body tissue.