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Implantable electrode assembly having reverse electrode configurationRelated Patent Categories: Surgery: Light, Thermal, And Electrical Application, Light, Thermal, And Electrical Application, Electrical Therapeutic SystemsImplantable electrode assembly having reverse electrode configuration description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070276442, Implantable electrode assembly having reverse electrode configuration. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCES TO RELATED APPLICATIONS [0001] The present application is a continuation of U.S. application Ser. No. 11/133,741 (Attorney Docket No.: 021433-001700US), filed May 19, 2005, the full disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION Field of the Invention [0002] The invention relates generally to medical devices and methods, and more particularly, to implantable electrodes for applying electrotherapy/electrostimulation that utilizes at least a pair of electrodes employing a reverse electrode configuration. [0003] Implantable electrode assemblies for electrotherapy or electrostimulation are well-known in the art. For example, various configurations of implantable electrodes are described in U.S. Patent Publication No. U.S. 2004/0010303, which is incorporated herein by reference in its entirety. One type of electrode assembly described therein is a surface-type stimulation electrode that generally includes a set of generally parallel elongate electrodes secured to, or formed on, a common substrate or base. Prior to implantation in a patient, the electrodes are generally electrically isolated from one another. Once the electrode assembly is implanted, one or more of the electrodes are utilized as a cathode(s), while one or more of the remaining electrodes are utilized as an anode(s). The implanted cathode(s) and anode(s) are electrically coupled via the target region of tissue to be treated or stimulated. [0004] One example of an application for this type of electrode assembly is for implantation onto a surface of tissue to be the target for electrotherapy or electrostimulation. The target tissue may have an irregular or complex shape, such as the outer surface of a blood vessel. The base or substrate and the electrodes of the electrode assembly can be sufficiently flexible to conform to the shape of the target tissue while maintaining a particular relative positioning of the electrodes. The geometry of the electrode assembly can be especially adapted for implantation at a particular site. For example, an electrode assembly can be sized and shaped to be implanted around the outside of the vascular wall such that the electrotherapy or electrostimulation can be focused on a particular target region. [0005] One known problem associated with state of the art implantable electrode arrangements of certain geometries is their tendency to produce non-uniform electric fields or currents in the target region under certain conditions. An example of such a condition is when the implantation site has a low enough impedance to approach that of the electrode materials. In such cases, the internal resistance of the implanted electrodes becomes a significant parameter in the electrical/electromagnetic model of the implanted electrode arrangements. This problem can become pronounced in electrode arrangements in which the size of the electrodes approaches or exceeds the general size of the target region, or in arrangements in which the electrodes have structural geometries other than merely point electrodes. [0006] Non-uniformity of electric field in the target region can result in sub-optimal electrotherapy or electrostimulation. Another consequence that occurs when the surface regions of implanted electrodes operate with disparate charge densities is an increased susceptibility of the electrodes to corrosion. Because corrosion is a charge density based phenomenon, increased concentrations of charge carriers in certain regions of the electrodes tends to focus faradaic processes responsible for corrosion at those regions. [0007] In U.S. Pat. No. 5,265,623, a defibrillation catheter is described having generally linear electrode geometries (elongate helical or spiral coils) that, when implanted, are both situated generally longitudinally in the heart. The electrodes of the defibrillation catheter are connected to the defibrillation energy source from a center point of each electrode, rather than at the ends thereof. This arrangement is intended to provide an improved field distribution around the catheter electrode and avoid high current densities at the electrode ends. The arrangement nevertheless operates with a charge density gradient in each electrode due to the construction and relative positioning of the electrodes. Thus, the applied electric signaling is not likely to be uniform along the length of the electrodes. Furthermore, the multi-layer or multi-axial construction of the disclosed catheter requires a complex and relatively expensive fabrication process. Moreover, the catheter electrode assembly is not suitable for the surface-type of implantation applications described above. [0008] While techniques have been developed to improve the distribution of electric field densities with respect to axial defibrillation electrode leads, it would be desirable to provide designs for implantable electrodes that improve the distribution of electrical field densities with respect to surface-type implantable electrodes. BRIEF SUMMARY OF THE INVENTION [0009] The present invention provides methods and apparatus for generating an electric field inside a patient that enhances the effective distribution of the density of the electric field. In one embodiment, at least a first and a second electrode are arranged on a common implantable substrate such that a proximal end of the first electrode is closer to a distal end of the second electrode and vice-versa. The electrodes are arranged and electrically connected to an energy source via the proximal ends such that when electrical energy is applied across the first and second electrodes, electrical current preferentially flows simultaneously through the first and second electrodes from the proximal end of one electrode to the distal end of the other electrode. In one aspect of the invention, the first and second electrodes are situated proximate a surface of tissue to be stimulated such that the electrodes are generally uniformly electrically coupled along their lengths via the tissue. [0010] A method of evenly distributing an electric field between at least a pair of implanted electrodes according to another aspect of the invention includes providing an implantable electrode assembly that includes at least two electrodes on a common substrate, wherein each electrode has an elongate shape and is situated generally equidistantly along its length from at least one of the other electrodes in a configuration where the proximal and distal ends of the electrodes are reversed between an anode and a cathode. Electrical energy is applied through the at least two electrodes such that a generally uniform current density is established between the anode and the cathode. [0011] An electrode assembly according to another aspect of the invention includes a generally flexible base and at least three generally parallel elongate electrode structures secured over a surface of the base, each electrode structure having a proximal end and a distal end. An outer pair of the electrode structures is electrically isolated from an inner electrode structure, and the proximal end of each electrode structure is electrically coupled to a conductive lead adapted to carry electrical energy. The proximal ends of the outer electrode structures and the distal end of the inner electrode structure are proximately situated at a first surface region of the base, and the distal ends of the outer electrode structures and the proximal end of the inner electrode structure are proximately situated at a second surface region of the base that is separate from the first surface region. [0012] Another aspect of the invention is directed to an electrode assembly implanted at an electrotherapy site in a patient, the electrode assembly comprising a substrate; at least two elongate electrodes secured to the substrate and electrically coupled to the electrotherapy site, each electrode having opposing ends proximally and distally situated; and an electrotherapy signal generator circuit electrically coupled with the at least two electrodes and supplying electrotherapy signaling to the electrotherapy site via the at least two electrodes. The electrical coupling facilitates a generally uniform charge density in the at least two electrodes. [0013] An electrotherapy arrangement implanted at an electrotherapy site according to another aspect of the invention comprises an electrode assembly that includes a substrate; and at least two elongate electrodes secured to the substrate and electrically coupled to the electrotherapy site, wherein each electrode is situated such that its proximal ends are longitudinally opposing. The electrotherapy arrangement further comprises an electrotherapy signal generator circuit electrically coupled with the at least two electrodes and applying electrotherapy signaling to the electrotherapy site via the at least two electrodes. The electrotherapy signaling generates an electric field through the electrotherapy site that is generally uniformly distributed along a longitudinal reference axis located in the electrotherapy site between the anode and cathode of the at least two electrodes. [0014] According to another aspect of the invention, an implantable electrode assembly includes an implantable substrate and three elongate electrodes secured to the substrate. Each electrode has respective proximal and distal opposing ends, and the electrodes are relatively situated such that each electrode is generally uniformly spaced along its length with respect to its adjacent electrode(s). The electrodes are also relatively spaced such that an inner electrode is flanked on two sides by a pair of outer electrodes. A first lead is connected to the inner electrode at the inner electrode's proximal end positioned on one side of the substrate, and second and third leads are connected to the outer electrodes at the respective proximal ends positioned on an opposite side of the substrate. In one embodiment, each of the leads for the outer electrodes are positioned on one side and the lead for the inner electrode is positioned on the opposite side. [0015] In an alternate embodiment, all of the leads are arranged on one side and a portion of the lead to the inner electrode is routed across the substrate within an insulator for the distal end of the lead to connect to the proximal end of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS [0016] The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: [0017] FIG. 1A is a top-view diagram illustrating an electrode assembly according to one embodiment of the present invention. [0018] FIG. 1B is a diagram illustrating one physical embodiment of the electrode assembly of FIG. 1A. [0019] FIG. 1C is a top-view diagram illustrating an electrode assembly having a particular wiring arrangement according to one embodiment of the invention. Continue reading about Implantable electrode assembly having reverse electrode configuration... 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