Abstract:
An electrically conductive member includes an elongate body, which has at least one electrically conductive region. The electrically conductive region comprises a porous polymeric material coated with an electrically conductive material. A method of manufacturing the electrically conductive member includes the steps of extruding an elongate body of polymeric material, wherein at least one region of the elongate body is porous in nature; and coating the elongate body with an electrically conductive material, such that the electrically conductive material substantially coats the pores of the at least one region.

Description:
This application is a continuation application under 35 U.S.C. §120 of U.S. Pat. application Ser. No. 11/123,392, filed May 5, 2005, now U.S. Pat. No. 7,629,015 issued Dec. 8, 2009 which is a divisional application under 35 U.S.C. §120 of U.S. Pat. application Ser. No. 10/399,845, filed Sept. 26, 2003 (acceptance date), now U.S. Pat. 7,625,617, issued Dec. 1, 2009, which is a U.S. National Stage application under U.S.C. §371 of Internationals Application No. PCT/AU01/01339, filed Oct. 19, 2001, which claims priority to Australian Provisional Patent Application No. PR903, filed Oct. 20, 2000. Each of the foregoing disclosures is herein incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to medical electrical leads and electrodes and, in particular, to medical leads having electrodes made from a metal-coated polymeric material. 
     BACKGROUND ART 
     Electrical leads and electrodes are commonly utilized in the medical field for applications such as stimulation, sensing, ablation and defibrillation. 
     Traditionally, medical electrodes comprise machined metal or coiled metal wire components, which, while suitably conductive, do not provide the flexibility in both design and mechanical properties afforded by a metal-coated polymer. Furthermore, metal-coated polymers are particularly suitable for use in larger area electrodes where their lightweight, flexibility and versatility are key advantages. 
     The use of metal-coated or metal-filled polymers as medical electrodes has been considered. For example, in U.S. Pat. No. 5,279,781, a metal-filled fiber for use as a defibrillation electrode is described. The metal in this case is added during the spinning process. To render the electrode suitably conductive, however, requires the addition of a significant proportion of metal to the fiber, which, in turn, has an adverse effect on the mechanical strength of the electrode. 
     Further structures, including metal-filled silicones and intrinsically conductive polymers, have been considered for use as medical electrodes although it has been found that such structures do not have the required level of conductivity necessary for the abovementioned medical applications. 
     Typically, the problem encountered with using a polymeric material as an electrode is that it is difficult to obtain a good electrical connection to the electrode. In U.S. Pat. No. 5,609,622, an electrical connection was achieved by utilizing an electrode having metal wires embedded in its wall. The electrode was then subjected to an ion beam treatment with metal, such that the metal was deposited within the wall and, therefore, contacted the wires. In this case, however, the electrical connection was only shown to occur at one end of the electrode and further, it is questionable whether a good connection is achieved by this method as it relies upon the incidence of metal contacting wire through the thickness of polymeric material. 
     The present invention provides an electrical lead and/or electrode that overcomes the problems of the prior art. 
     Any discussion of documents, acts, materials, devices, articles, or the like, which has been included in the present specification, is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. 
     DISCLOSURE OF THE INVENTION 
     Throughout this specification, the word “comprise,” or variations such as “comprises” or “comprising, ” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. 
     According to a first aspect, the present invention may include an electrically conductive member including an elongate body, the body having at least one electrically conductive region, the region comprising a porous polymeric material coated with an electrically conductive material. 
     Preferably, the electrically conductive member is adapted for medical use and, in particular, but not limited to, use in cardiac mapping, defibrillation or pacing, neurological applications including neural stimulation implants, muscle stimulation, sensing and ablation. Accordingly, in a preferred embodiment, the electrically conductive member may comprise part of a lead or any other form of carrier. 
     Typically, the electrically conductive member is an elongate tube. While the entire length of the member may be made from a porous polymer coated with an electrically conductive material, it is also envisaged that the electrically conductive member may comprise a plurality of distinct electrically conductive regions made up of the coated porous polymer. 
     In the embodiment wherein the electrically conductive member is tubular, it is preferred that the pores of the at least one electrically conductive region are present substantially across the diameter of a sidewall of the tubular structure. Accordingly, in this embodiment, electrical connection may be made from internal a lumen of the tube. It is further envisaged that electrical connection may be made from within the sidewall of the tube as further discussed below. 
     Rather than a tube, the electrically conductive member may comprise a solid cylindrical member. In this embodiment, it is again preferred that the pores of the at least one electrically conductive region are present substantially across the diameter of the cylindrical member. 
     In a preferred embodiment, the pores of the polymeric material of the at least one electrically conductive region are greater than 5 microns and preferably between 30 microns and 100 microns. When the porous polymeric material is coated with an electrically conductive material, the electrically conductive material preferably coats and lines at least some of, and preferably all of, the pores. 
     Typically, the electrically conductive material is a metal and, preferably, a biocompatible metal such as platinum. It is envisaged, however, that a combination of two or more metals or metal alloys may be used to improve electrical conductivity. For example, it may be desirable to provide a first layer of copper or silver or any other suitably conductive metal and a second layer of platinum to enable use of the electrically conductive member within a body. 
     The coating of the porous polymeric material preferably creates a suitably thick layer of metal coating across the at least one electrically conductive region. Preferably, the resistance of the coating is less than 100 ohms and more preferably less than 10 ohms. 
     The porous polymeric material may be expanded polytetrafluoroethylene (PTFE), wherein the pore size is adjusted to allow the metal coating to penetrate the pores and to produce a coating of sufficient thickness to provide adequate electrical conductivity. Other materials are envisaged including, but not limited to, porous silicones, porous polyurethanes, polyether block amide (PEBAX) or nylon. In each case, the pore size may be varied depending upon the method of formation of the porous material or by the addition of additives such as sodium chloride (NaCl), sodium bicarbonate (Na 2 HCO 3 ) or polyglycolide, which can be leached out following molding or extrusion, leaving a porous structure. 
     Alternatively, the pores of the polymeric material may be formed by drilling into the polymer using a laser drill. This has the particular advantage of enabling only a portion of the polymer to be of a porous nature. 
     The at least one electrically conductive region may be electrically connected to an electrical conductor. 
     In one embodiment, the electrical conductor is a straight or coiled wire, or number of wires, embedded within the body of the electrically conductive member and preferably within the at least one electrically conductive region of the member. If the electrically conductive member is a solid cylindrical member, the wire or wires may be coiled in a helical manner within the at least one electrically conductive region. If the electrically conductive member is a tubular structure, the wire or wires may be coiled in a helical manner within the wall of the tube and preferably within the at least one electrically conductive region. In either embodiment, the wire(s) may extend through several pores of the at least one electrically conductive region. Accordingly, when the porous polymeric material of the at least one region is coated with the electrically conductive material, the portions of wire that extend through the pores may be simultaneously coated with the electrically conductive material, thereby creating a good electrical connection between the electrical conductor and the electrically conductive region. 
     The wires may be single wires or multifilament wires. Further, the wire or wires may be made of copper, preferably coated with a noble metal, such as palladium or platinum, for corrosion resistance. Alternatively, the individual wires may be a multifilament stainless steel wire. Other suitable materials include, but are not limited to, platinum or platinum alloy, MP35N or ELGILOY®. 
     In the above embodiment, depending upon the application of the electrically conductive member, the wire(s) may be connected by an insulated conductor to either a source of electricity or to an analyzer means. Typically, the wire(s) are connected to the insulated conductor by way of welding. Alternatively, they may be connected by electrically conductive adhesives or by soldering. 
     In a further embodiment, the electrical conductor is located internal the elongate body of the electrically conductive member. For example, if the electrically conductive member is a tube having at least one electrically conductive region, the electrical conductor may be positioned within the lumen of the tube. In this embodiment, the electrical conductor is preferably adapted such that it engages the internal surface of the tube. To ensure that the electrical conductor engages the tube, it is preferred that the electrical conductor comprises a resilient spring, such as a spiral spring, that, once positioned in the tube, can expand into contact with the inner wall of the tube. 
     In another embodiment, the electrical conductor may be a spring formed from a shape memory alloy such as Nitinol. The shape memory spring preferably moves, when exposed to a pre-determined temperature, from a first position to a second position, wherein, when in the second position, the spring expands such that it has an outer diameter greater than the inner diameter of the tube. Accordingly, when internal the lumen of the tube and when in the expanded second position, the spring engages the inner surface of the tube to a sufficient extent to provide a good electrical connection between the electrical conductor and the at least one electrically conductive region. 
     In one embodiment, the shape memory alloy spring expands into contact with the inner surface of the tube upon exposure to body temperature. 
     The shape memory spring may be connected to an insulated conductor by welding, the use of electrically conductive adhesives or soldering. 
     In the above embodiments, it is preferred that the electrical conductor such as the wire(s) embedded within the electrically conductive member or a shape memory alloy spring positioned within a lumen of a tubular electrically conductive member, extends the entire length of the electrically conductive member, or at least the length of the at least one electrically conductive region, such that a good electrical connection between the electrical conductor and the at least one electrically conductive region can be made. 
     In another embodiment, the electrical conductor is adapted to engage an end of the electrically conductive member. For example, the electrical conductor may include a shape memory alloy tube that is adapted to expand and increase its internal diameter upon heating above a pre-determined temperature or exposure to a particular pre-determined temperature. The shape memory alloy tube may then be slid over an end of the electrically conductive member. Upon heating above or cooling below the pre-determined temperature depending on the type of shape memory alloy, the shape memory alloy tube preferably returns to its original unexpanded shape, therefore, effectively clamping down on an end of the electrically conductive member. This embodiment provides a uniform radial pressure on the end of the member and provides a good electrical connection between the electrical conductor and the at least one electrically conductive region of the member. If the electrically conductive member is a tube, it may be necessary to provide an inner tube which is relatively stiff and which may be positioned internal the lumen of the tube to prevent collapse of the member. 
     In a second aspect, the present invention may include a method of manufacturing the electrically conductive member of the first aspect, the method comprising the steps of: 
     (i) extruding an elongate body of polymeric material, wherein at least one region of the elongate body is porous in nature; and 
     (ii) coating the elongate body with an electrically conductive material such that the electrically conductive material substantially coats the pores of the at least one region. 
     While the entire length of the elongate body may be coated with the electrically conductive material, in the embodiment wherein there are distinct regions of porous polymeric material, it may be preferred that only the distinct porous regions are coated with the electrically conductive material rather than the entire length of the elongate body, which may include non-porous regions. 
     Where the electrical conductor comprises a straight or coiled wire, the electrically conductive member may be manufactured in a number of stages. For example, a first tube, or layer, or solid cylindrical member may be formed from either a porous polymeric material or non-porous polymeric material or a combination thereof. The wire may then be wrapped around and along at least a portion of the first tube or solid cylindrical member in a helical manner or extended along at least a portion of the length of the first tube or layer or solid cylindrical member. The wire and the first tube or layer or solid cylindrical member may then be overlaid with a coating or another layer. The coating or the other layer may be a porous polymeric material or, alternatively, a polymeric material having regions that are of a porous nature. In one embodiment, the coating may be a second tube. 
     In a further embodiment of the second aspect, the electrically conductive member may comprise a tube. In this embodiment, the electrical conductor is positioned within the lumen of the tube. The electrical conductor is preferably positioned such that it engages the internal surface of the tube. To ensure that the electrical conductor engages the tube, it is preferred that the electrical conductor comprises a resilient spring, such as a spiral spring that, once positioned in the tube, can expand into contact with the inner wall of the tube. 
     In another embodiment of the second aspect, the electrical conductor can be formed in a spring form from a shape memory alloy such as Nitinol. The shape memory spring can preferably move from a first position to a second position, wherein, when in the second position, the spring could expand such that it had an outer diameter greater than the inner diameter of the tube. 
     The electrical conductor may be adapted to engage an end of the electrically conductive member. For example, the electrical conductor may include a shape memory alloy tube that is adapted to expand and increase its internal diameter upon heating above a pre-determined temperature. The shape memory alloy tube may then be slid over an end of the electrically conductive member. Upon heating above or cooling below the pre-determined temperature depending on the type of shape memory alloy, the shape memory alloy tube preferably returns to its original unexpanded shape, therefore effectively clamping down on an end of the electrically conductive member. This embodiment provides a uniform radial pressure on the end of the electrically conductive member and provides a good electrical connection between the electrical conductor and the at least one electrically conductive region of the member. 
     Typically, the electrically conductive material is applied to the elongate body or preferably to the at least one electrically conductive region using a wet technique such as electroless plating. In this embodiment, the electrically conductive material may be forced through the pores of the at least one electrically conductive region by the application of pressure. 
     Alternatively, the electrically conductive material may be applied by electroless plating followed by the additional step of electroplating. 
     Each of the above processes preferably ensures that a coating of electrically conductive material penetrates substantially all the pores of the electrode. If the at least one region of electrically conductive material has pores disposed substantially throughout the entire thickness of the region, it is envisaged that electrical connection may be made by way of an electrical conductor, as described above, either within the wall of the elongate body or on the inside of the elongate body (for example, if the elongate body is a tubular structure). 
     The process of coating the elongate body with an electrically conductive material such that the pores of the at least one electrically conductive region are coated with such a material may involve a number of steps prior to the actual coating with the electrically conductive material. The steps include: 
     (1) Cleaning. 
     (2) Surface Modification. 
     (3) Catalysis. 
     (4) Coating.
     (1) The material to be coated is typically washed in an organic solvent, such as acetone or ethyl acetate, or in a solution containing a suitable surface active agent. Usually some agitation is required, such as from an ultrasonic cleaner or a shaker water bath. The step of cleaning may be carried out above room temperature.   (2) The step of surface modification results in a more wettable or hydrophilic surface, such that the deposition of the coating may be accelerated and, further, chemical and mechanical adhesion of the coating to the surface may be improved.   

     Chemical adhesion may be improved by creating the most suitable functional groups on the surface of the polymer such as amides, while mechanical adhesion may be improved by creating a roughened surface using chemical (etching) or mechanical (sandblasting) methods. 
     Typically, the surface modification chemicals are infused into the pores using pressure via a pump or syringe. Alternatively, the porous material to be coated may be placed in the treatment solution and evacuated in a vacuum, thereby removing gas bubbles from within the porous structure resulting in contact of all surfaces with the treatment solution. 
     Additionally, plasma treatment may be used to improve wettability and/or improve chemical or mechanical adhesion. 
     Following this step, the structure to be coated is rinsed several times, preferably in deionized water.
     (3) The catalyst step results in the deposition of a small amount of noble metal on the surface of the material. This provides the sites for deposition of the coating material, for example, platinum. While typical electroless plating uses a tin/palladium catalyst, it is preferred that a process that eliminates the tin is used. For example, palladium in an acidic aqueous solution or dimethyl sulfoxide, both of which can be reduced in a hydrazine solution, is preferred. The latter is particularly useful as, being an organic solution, it allows improved wettability for many substrates.   

     In one embodiment of the catalysis of a material such as silicone, the catalyst, in the form of palladium metal powder, can be mixed into a silicone dispersed in a solvent and then infused into the pores and cured prior to coating. In this embodiment, a small concentration of actual silicone is required so as to provide a thin layer on the surface of the pores rather than fill the pores with silicone. The palladium metal will act as a catalyst and will be bound to the silicone and, therefore, increase the adhesion of the coating material that is subsequently applied. 
     Alternatively, the silicone mix may be infused with palladium prior to molding or extrusion. 
     The catalyst step may be performed a number of times.
     (4) The coating process preferably uses electroless plating, wherein a number of metals may be deposited using either commercially available or custom made solutions of complex metal ions, together with a stabilizer and an added reducer. The solution typically allows controlled deposition of a metal over a specific period of time. If a biocompatible electrode is required, it is preferred that the metal is platinum.   

     A fifth step may be added to the above process if a thicker coating of metal and, therefore, higher conductivity is required. This would involve further electroless plating or electroplating. 
     In a further embodiment, following the process of coating, the pores are infused with a liquid adhesive such as, but not limited to, a silicone dispersant to effectively seal the pores. Preferably, the infusion of the adhesive is carried out from within the electrically conductive member when the member is a tubular structure. This embodiment has the advantage of enabling an electrically conductive member to be implanted in a body for long periods of time with minimal tissue ingrowth into the member. This facilitates easy removal of the member if required. 
     In a third aspect, the present invention may include an electrically conductive member including an elongate body, the elongate body having at least one electrically conductive region comprising a polymeric material, together with at least one electrical conductor wherein at least a portion of the polymeric material and at least a portion of the at least one electrical conductor have a coating thereon of an electrically conductive material. 
     Preferably, the elongate body comprises a tubular body made of a suitable polymer material. The electrical conductor is preferably housed within at least part of a side wall of the tubular body. In addition to being housed within a side wall of the tubular body at the at least one electrically conductive region of the body, the electrical conductor may extend along the entire length of the tubular body. 
     The elongate body preferably comprises a first cylindrical inner member and a second outer member, the second outer member substantially forming a coating around the first inner member. The second outer member preferably extends over the entire length of the first inner member. The at least one electrical conductor is preferably sandwiched between the first inner member and the second outer member. 
     The first inner member may be made from a suitable polymeric material such as polyurethane, polyether block amide (PEBAX), PEEK or polyimide. The second outer member is preferably formed from a similar polymeric material to that of the first inner member. Further, it is preferred that the second outer member is made from a transparent, or at least substantially transparent, material such that the at least one electrical conductor may be viewed through the second outer member. 
     Preferably, the second outer member is much thinner than the first inner member and typically, the second outer member is sufficiently thick to only just cover the at least one electrical conductor. 
     The at least one electrical conductor may comprise a metal wire or wires made from material such as PFA, polyimide insulated copper wire(s) or copper alloy wire(s). Preferably, the wire(s) have a diameter of approximately 0.025 mm to 0.3 mm. 
     Typically, during manufacture, single wires may be wound substantially around the circumference of the first inner member. Preferably, between 8 to 24 wires are wound around the first inner member in this manner, wherein each wire has a predetermined spacing between it and the next wire. These 8 to 24 wires may form a particular group that is spaced from a second or subsequent group of wires by a gap, which is preferably larger than the gap between each wire of each group. In this way, identification of each group may be more easily determined. To aid identification, each group may further be color coded. 
     The at least one electrical conductor may be helically wound around the first inner member. However, the present invention is not limited to the particular arrangement of the at least one electrical conductor and a number of combinations and orientations are envisaged. 
     Preferably, at least one portion of the at least one electrical conductor is not overlaid by the second outer member, that is, the at least one portion is exposed to the outside environment. The at least one portion of the electrical conductor of this embodiment is preferably coated with the electrically conductive material. It is further preferred that at least a portion of the polymeric elongate body adjacent the exposed portion of the electrical conductor is also coated with the electrically conductive material. 
     Typically, a band around the circumference of the elongate body is coated, together with the exposed portion of the electrical conductor, to form a band electrode on the elongate body. 
     Preferably, the electrically conductive material is a metal and, preferably, a biocompatible metal such as platinum. It is envisaged that a combination of two or more metals or metal alloys may be used, however, to improve electrical conductivity. For example, it may be desirable to provide a first layer of copper or silver or any other suitably conductive metal and a second layer of platinum to enable use of the electrically conductive member within a body. 
     It is preferred that the exposed at least one portion of the electrical conductor is protected from corrosion. This may be achieved by, for example, immersing the elongate body in a solution such as palladium chloride, which will coat the exposed portion(s). 
     In a fourth aspect, the present invention provides a method of manufacturing an electrically conductive member, the method comprising the steps of: 
     (i) extruding an elongate inner member from a polymeric material; 
     (ii) applying at least one electrical conductor to an exposed surface of the inner member; 
     (iii) overlaying the inner member and the at least one electrical conductor with an outer member made from a polymeric material, such that the at least one electrical conductor is covered by the outer member; 
     (iv) exposing at least a portion of the at least one electrical conductor; and 
     (v) coating the exposed portion of the at least one electrical conductor and at least a portion of the outer member with an electrically conductive material. 
     Preferably, the inner member is extruded as a tube made from a suitable material such as polyurethane or polyether block amide (PEBAX). 
     The at least one portion of the at least one electrical conductor may be exposed by a number of means including, but not limited to, applying heat, chemicals or lasers to remove the area of the outer layer covering the at least one portion. Desirably, a laser technique is used (e.g., quadruple Yag laser) as such a technique provides good accuracy. For example, the laser beam is capable of following a particular path of, say, a helically wound wire acting as the at least one electrical conductor. While only a small portion of the at least one electrical conductor may be exposed in this manner, the present invention is not limited to the amount of electrical conductor exposed and, indeed, the entire electrical conductor may be exposed. 
     For high energy applications, such as radio frequency (RF) or microwave ablation, adjacent electrical conductors may be exposed and coated with electrically conductive material to form a single electrode. Such a configuration decreases the current density. The electrical conductors of this embodiment may be electrically connected to each other at a proximal end of each electrical conductor. The number of electrodes formed together with the spacing between each electrode may be varied. 
     The exposed portion of electrical conductor(s) may be protected from corrosion by immersion in an acidic solution of, for example, palladium chloride, which will coat all the exposed portions. 
     It is desirable that the at least one portion of the at least one electrical conductor and at least a portion of the elongate body, which together are coated to form an electrode, are catalyzed. To prevent catalysis of the remainder of the elongate body or electrical conductor that form a non-electrode area, these areas are protected from catalysis by masking them by, for example, photolithography or by using pieces of heat shrink tubing such as PET to protect the areas. An alternative to masking is the use of an ink that is pad printed over the areas to be coated and, thus, the areas that are to become the electrodes. The ink used may or may not be electrically conductive but, in any event, should be able to catalyze a subsequent plating step. If radio opacity is required, it may be desirable to use an ink including colloidal palladium or silver. 
     The catalyst step results in the deposition of a small amount of noble metal on the surface of the material to be coated. This provides the sites for deposition of the electrically conductive material, for example, platinum. While typical electroless plating uses a tin/palladium catalyst, it is preferred that a process that eliminates the tin is used. For example, palladium in an acidic aqueous solution or dimethyl sulfoxide, both of which can be reduced in a hydrazine solution, is preferred. The latter is particularly useful as, being an organic solution, it allows improved wettability for many substrates. 
     The catalyst step may be performed a number of times. 
     The coating process preferably uses electroless plating, wherein a number of metals may be deposited using either commercially available or custom made solutions of complex metal ions, together with a stabilizer and an added reducer. The solution typically allows controlled deposition of a metal over a specific period of time. If a biocompatible electrode is required, it is preferred that the metal is platinum. 
     If relatively thick coatings are required, it is preferred that a porous polymer is used. 
     The electrodes formed with respect to the third and fourth embodiments may be protected by a layer of, for example, polyethylene glycol or mannitol. Such a protective layer preferably allows an electrical charge to pass therethrough. 
     The following examples describe the preparation of the electrode according to several embodiments of the first and second aspects of the present invention. 
     EXAMPLE 1 
     A porous polyurethane tube was made using a spraying system. First, a wire mandrel was connected to an electrical motor using a chuck. The wire was simultaneously coated with a mixture of polyurethane (PELLETHANE®) dissolved in dimethylformamide (1% polyurethane) and water. The water polymerized the polyurethane prior to deposition, creating a porous layer. A copper wire was then wound onto the coated mandrel and a further layer was uniformly coated with the mixture of polyurethane dissolved in dimethylformamide and water. The spraying continued until the appropriate diameter was achieved, i.e., 2.2 mm (this was chosen as once assembled into a lead, a 2.2 mm lead body would comfortably pass down a 7 French introducer). 
     The porous component was then coated with platinum using the normal cleaning, surface modification, catalysis and coating steps previously outlined. 
     The resistance was then measured to be approximately 0.5Ω for a 1 cm length of the porous component, and approximately 1Ω from the end of the copper wire to the surface of the component. 
     EXAMPLE 2 
     An expanded PTFE tube was supplied by Impra, which had a pore size of 30 microns. The tube was immersed in alcohol and placed in an ultrasonic cleaner to remove air bubbles and wet the surface. 
     The sample was removed from the alcohol and etched for 1 minute with FLUOROETCH® from Acton Technologies, Inc., Pittson, PA. A syringe was used to try and force the solution through the pores; however, this was unsuccessful. 
     The tube was then catalyzed using a 2 g/l solution of PdCl 2  in Dimethyl Sulfoxide for 5 minutes, intermittently attempting to force the solutions through the pores. This was followed by a reduction step in 4% Hydrazine solution. 
     The catalyzed tube was then electrolessly coated using a platinum complex solution and hydrazine. 
     After 1.5 hours, the sample was a shiny, metallic color on the outside. 
     After drying, the resistance along the surface was found to be approximately 20Ω for a 1 cm length; however, the resistance through the thickness varied from 25-50Ω. 
     EXAMPLE 3 
     Another expanded PTFE tube was supplied by Impra; however, this time, the pore size was increased to 90 microns. The tube was immersed in alcohol and placed in an ultrasonic cleaner to remove air bubbles and wet the surface. 
     The sample was removed from the alcohol and etched for 30 seconds with FLUOROETCH® from Acton Technologies, Inc., Pittson, PA. A syringe was used to try and force the solution through the pores. This time, the solution was able to freely pass through the structure. 
     The tube was then catalyzed using a 2 g/l solution of PdCl 2  in Dimethyl Sulfoxide for 5 minutes, intermittently forcing the solutions through the pores. This was followed by a reduction step in 4% Hydrazine solution. 
     The catalyzed tube was then electrolessly coated using a platinum complex solution and hydrazine, intermittently forcing the solution through the pores. 
     After 1.5 hours, the sample was a shiny, metallic color on the outside. 
     After drying, the resistance along the surface was found to be approximately 1.5Ω for a 1 cm length. The resistance through the thickness was approximately 1.5Ω. No materials were removed using a standard tape test to measure adhesion. 
     A 4 mm length was then cut and a 2.1 mm diameter Nitinol spring (from Microvena, White Bear Lake, Minnesota, USA) was straightened and passed up the middle of the cut platinum-coated tube. The structure was then placed in the oven at 70° C. and the Nitinol spring went back to its original shape clamping on the inside of the platinum-coated tube. 
     A length of 0.2 mm diameter copper wire was then welded to one end of the Nitinol spring. The resistance was found to be 1.8 ohms from the end of the copper wire and the outside of the platinum-coated expanded TEFLON®. 
     A PEBAX tube was passed over each end of the spring and then glued with epoxy forming a butt joint on each side of the platinum-coated expanded TEFLON® component. 
     After curing, the lead was then tested in an isolated cow heart, by immersing the heart with an electrode attached into a conductive media and RF energy passed through the electrode to the heart, creating lesions. The test device produced similar lesions to a commercially available ablation lead. 
     The same lead was tested when delivering pacing pulses and a suitable impedance resulted. 
     Due to flexibility and versatility, the electrodes can be made different shapes, sizes, numbers and spacing. This is important when designing new leads for various applications, e.g., ablation leads for treating atrial fibrillation. 
     The following examples describe the preparation of the electrode according to several embodiments of the third and fourth aspects of the present invention. 
     EXAMPLE 4 
     A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland, Oregon. The cable contained eight insulated wire coils in the wall of the tube. The insulating layer was made from a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink from Creative Materials Tyngsboro, MA was coated around the unmasked region covering the exposed conductor. The electrode with ink was then immersed in a platinum complex electroless bath and coated for 1 hour at 60° C. using Hydrazine as the reducer resulting in a thickness of 0.5 micron. The pacing impedance of the plated electrode was then measured in a 0.18% NaCl solution using a nickel plate as the return electrode. The pacing pulse used was 5 volts for 0.5 ms. The impedance was found to be 250 ohms. This value was compared to a commercially available ablation electrode, which was found to be 180 ohms. No damage to the coated electrode resulted. 
     EXAMPLE 5 
     A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland, Oregon. The cable contained eight insulated wire coils in the wall of the tube. The insulating layer was a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink (CMI 117-31) from Creative Materials Inc., Tyngsboro MA was coated around the unmasked region covering the exposed conductor. The electrode ink was coated with a 3 micron layer of copper using electroless plating. The copper-coated electrode was then immersed in an acid palladium chloride solution to catalyze the surface and immersed again in platinum complex electroless bath and coated for 1 hour at 60° C. using Hydrazine as the reducer. The pacing impedance of the plated electrode was then measured in a 0.18% NaCl solution using a nickel plate as the return electrode. The pacing pulse used was 5 volts for 0.5 ms. The impedance was found to be 120 ohms. This value was compared to a commercially available ablation electrode, which was measured to be 180 ohms. No damage to the coated electrode resulted. 
     EXAMPLE 6 
     A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland, Oregon. The cable contained eight insulated wire coils in the wall of the tube. The insulating layer was a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink (CMI  117 - 31 ) from Creative Materials, Inc., Tyngsboro MA was coated around the unmasked region covering the exposed conductor. The electrode ink was coated with a 3 micron layer of copper using electroless plating. The copper-coated electrode was then immersed in an acid palladium chloride solution to catalyze the surface and immersed again in platinum complex electroless bath and coated for 1 hour at 60° C. using Hydrazine as the reducer. 
     The electrode was then placed on a piece of meat immersed in a 0.18% solution of NaCl and a stainless steel return electrode underneath. High-frequency RF power was delivered through the electrode for 60 seconds, resulting in a lesion similar to a commercially available ablation electrode. 
     EXAMPLE 7 
     A 1.6 mm diameter cable was sourced from MicroHelix, Inc., Portland, Oregon. The cable contained eight insulated wire coils in the wall of the tube. The insulating layer was a thin layer of PEBAX. Over one of the wires, a 4 mm length of insulation was removed to expose the corresponding amount of wire. A 4 mm band of the cable around the exposed wire was masked. Some plateable conductive ink (CMI 117-31) from Creative Materials, Tyngsboro, MA was coated around the unmasked region covering the exposed conductor. The electrode ink was coated with a 3-micron layer of copper using electroless plating. The copper-coated electrode was then immersed in an acid palladium chloride solution to catalyze the surface and immersed again in platinum complex electroless bath and coated for 1 hour at 60° C. using Hydrazine as the reducer. 
     The coated electrode was then immersed in a 0.18% NaCl solution using a nickel plate as the return electrode. A biphasic defibrillation pulse 130 volts in amplitude and 6 ms in pulse width was delivered through the coated electrode, which resulted in no damage to the electrode and an impedance of 130 ohms. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are now described with reference to the accompanying drawings, in which: 
         FIGS. 1   a ,  1   b , and  1   c  are side elevational views illustrating a construction of one embodiment of the present invention; 
         FIGS. 2   a ,  2   b , and  2   c  are cross-sectional views through I-I of  FIGS. 1   a ,  1   b , and  1   c  respectively; 
         FIG. 3  is a side elevational view of a cut-away portion of an embodiment of the invention; 
         FIGS. 4   a  and  4   b  are part cut-away, part side elevational views of a further embodiment of the invention; 
         FIGS. 5   a  and  5   b  are side elevational views of a further embodiment of the invention; 
         FIG. 6  is a schematic view of a multi-electrode assembly incorporating electrically conductive regions of the present invention; 
         FIG. 7  is a perspective view of a number of electrically conductive regions of the present invention in an electrode assembly; 
         FIGS. 8   a ,  8   b , and  8   c  are schematic views showing the steps of manufacture of an electrically conductive member according to a further aspect of the invention; 
         FIGS. 9   a ,  9   b , and  9   c  are schematic views showing the steps of manufacture of an electrically conductive member of another embodiment of the aspect depicted in  FIGS. 8   a ,  8   b , and  8   c ; and 
         FIGS. 10   a ,  10   b , and  10   c  are schematic views showing the steps of manufacture of an electrically conductive member of a further embodiment of the aspect depicted in  FIGS. 8   a ,  8   b , and  8   c.    
     
    
    
     DETAILED DESCRIPTION  
     The lead  10  of the present invention includes an elongate body  11  having at least one electrically conductive region  20  thereof made from a porous polymeric material. The porous polymeric material is coated with an electrically conductive material and preferably a metal such as platinum. 
     As discussed above, the lead  10  of the present invention is adapted for medical use and, in particular, use in cardiac mapping, defibrillation or pacing, neurological applications including neural stimulation implants, muscle stimulation, sensing and ablation. 
     As depicted in the drawings, the lead  10  has a tubular structure having a wall  12  and an internal lumen  13 . While only one region  20  of the tube may be made from the porous polymeric material, it may be preferable that the entire length of the tube is made from the material. 
     The pores within the wall  12  are preferably greater than 5 microns and preferably between 30 microns and 100 microns. 
     The coating of the porous polymeric material with the metal creates a suitably thick layer of metal coating, thereby increasing electrical conductivity through the lead  10 . 
     To establish a good electrical connection, the lead  10  includes a conductive member  14 . 
     In one embodiment, depicted in  FIGS. 1   a ,  1   b ,  1   c , the conductive member  14  comprises a coiled wire  15  embedded within a wall  12  of the lead  10 ( FIG. 2     1   ). The wire  15  is wrapped around and along a substantial length of the lead  10  and preferably along the entire lead. While not shown, the wire  15  may pass through several pores of the polymeric material and, thus, when the porous polymer is coated with the metal, the portions of wire  15  within the pores may simultaneously be coated with the metal, thereby creating a good electrical connection between the wire and the at least one electrically conductive region  20 . 
     As shown in  FIGS. 1   a ,  1   b  and  1   c , the lead of this embodiment may be made in a number of stages. A first tube  16  is created as shown in  FIG. 1   a . The first tube  16  may, or may not be, porous in nature. The wire  15  is subsequently wrapped around and along the first tube  16  in a helical manner and the wire  15  and first tube  16  subsequently overlayed with a second porous polymer material  17 ( FIG. 3 ). 
     In another embodiment, the conductive member  14  is a shape memory alloy spring  18 ( FIGS. 4     1   and  4   b ) such as a Nitinol spring. The spring  18  of this embodiment is positioned internal the lumen  13  of the lead  10 . In use, the spring  18  may be exposed to a pre-determined temperature that causes it to expand such that it abuts with the internal surface  19  of the lead  10 . Preferably, the spring  18  can normally expand to such an extent that its external diameter is greater than the diameter of the lumen  13  resulting in a good electrical connection between the spring and the at least one electrically conductive region. 
     In another embodiment of the invention depicted in  FIGS. 5   a  and  5   b , the conductive member  14  is adapted to engage one end  21  of the lead  10 . Preferably, the conductive member is a shape memory alloy tube  22 , which is adapted to expand and increase its internal diameter upon heating above or cooling below a pre-determined temperature depending on the type of shape memory alloy. The shape memory alloy tube  22  may then be slid over the end  21  of the lead  10 . Upon heating up or cooling below the pre-determined temperature depending on the type of shape memory alloy, the shape memory alloy tube  22  returns to its original unexpanded shape, therefore, effectively clamping down on an end of the lead  10  as shown in  FIG. 5   b . Accordingly, there is provided a uniform radial pressure on the end  21  of the lead  10 , which results in a good electrical connection between the shape memory alloy tube  22  and the at least one electrically conductive region. In this embodiment, it may be necessary to provide an inner, relatively stiff tube (not shown), which may be positioned internal the electrode  10  to prevent collapse of the lead  10 . 
     Once the lead  10  has been coated with the selected metal, the lead  10  may be cut to the desired length depending on the application of the electrode. For example, a defibrillation electrode formed from the lead may need to be a length of around 60 mm, whereas a lead acting as an electrode for mapping or sensing need only be a few millimeters in length. 
     A multi-electrode system along a lead may be constructed by threading together lengths of coated tubes  23  or uncoated tubes  24  of specified lengths as depicted in  FIG. 6 . The coated tubes  23  and uncoated tubes  24  are joined together using butt joints, which may have spring or tubing supports (not shown) within the lumen of the respective coated and uncoated tubes  23  or  24 . 
     In the aspect of the invention depicted in  FIGS. 8   a ,  8   b  and  8   c , the invention consists of an electrically conductive member  30  including an elongate body  31 . The elongate body  31  has at least one electrically conductive region  32 , which comprises a polymeric material  33 , together with at least one electrical conductor  34 . A portion of the polymeric material  33  and a portion or all of the electrical conductor  34  are coated with an electrically conductive material  35 . 
     The elongate body  31  comprises cylindrical first inner member  36  and a second outer member  37 , the second outer member  37  substantially forming a coating around the first inner member  36 . The second outer member  37  extends substantially over the entire length of the first inner member  36 . The at least one electrical conductor  34  is sandwiched between the first inner member  36  and the second outer member  37 . 
     As shown in  FIG. 8   b , the electrical conductor  34  is exposed. This may be achieved by a number of means including the application of heat, chemicals or lasers to remove the area of the outer member  37  covering the electrical conductor  34 . 
     The exposed electrical conductor  34  and an area of the polymeric material  33  adjacent the electrical conductor  34  is then catalyzed and coated with the electrically conductive material  35  to form an electrode  38 . 
     As depicted in  FIGS. 9   a ,  9   b , and  9   c , two electrodes  38  may be formed by coating separate electrical conductors  34  together with an adjacent area of polymeric material  33 . 
     For high energy applications such as RF or microwave ablation,  FIGS. 10   a ,  10   b  and  10   c  show how a number of electrical conductors  34 , together with their adjacent polymeric material  33 , may be coated with an electrically conductive material to form a single electrode  38 . The electrical conductors  34  of this embodiment may be electrically connected to each other at a proximal end of each electrical conductor  34 . The number of electrodes  38  formed together with the spacing between each electrode  38  may be varied. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.