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ROUTING AN ELECTRICAL CURRENT INDUCED IN AN ELECTRICAL
LEAD CONDUCTOR DISPOSED WITHIN BODY TISSUE TO A PLURALITY
OF ELECTRODES ELECTRICALLY COUPLED WITH THE BODY TISSUE
VIA A CIRCUIT WITHIN AN END CAP ATTACHED TO THE ELECTRICAL
METHOD AND APPARATUS FOR SHUNTING INDUCED CURRENTS IN AN ELECTRICAL LEAD
FIELD OF THE INVENTION
 This invention generally relates to implantable medical devices and, more specifically, to a method and apparatus for shunting electrical currents induced in an abandoned electrical lead.
DESCRIPTION OF THE RELATED ART
 Since the introduction of the first implantable pacemakers in the 1960s, there have been considerable advancements in both the fields of electronics and medicine, such that there is presently a wide assortment of commercially available body-implantable electronic medical devices. The class of implantable medical devices now includes therapeutic and diagnostic devices, such as pacemakers, cardioverters, defibrillators, neural stimulators, and drug administering devices, among others. Today's state-of-the-art implantable medical devices are vastly more sophisticated and complex than their early counterparts, and are capable of performing significantly more complex tasks. The therapeutic benefits of such devices have been well proven.
 Modern electrical therapeutic and diagnostic devices for the heart require a reliable electrical connection between the device and a region of the heart. Typically, an electrical contact, commonly referred to as a "lead," is used for the desired electrical connection. One type of commonly used implantable lead is a transvenous lead. Transvenous leads are generally positioned through the venous system to attach and/or electrically connect at their distal end via a tip electrode to the heart. At their proximal end, they are typically connected to the electrical therapeutic and/or diagnostic device, which may be implanted. Such leads normally take the form of a long, flexible, insulated conductor. Among the many advantages of transvenous leads is that they permit an electrical contact with the heart without physically exposing the heart itself, i.e., major thoracic surgery is not required.
 The leads may have various numbers of electrodes electrically coupled to the conductors. For example, unipolar leads may have a conductor leading to and electrically coupled with an electrode at the distal tip of the lead. Bipolar leads may, for example, have one conductor leading to and electrically coupled with an electrode at the distal tip of the lead and a ring electrode disposed some distance the tip electrode. Other leads may have one or more electrode coils, for example, in addition to tip and/or ring electrodes, for delivering defibrillating shocks to a patient.
 It may become desirable in certain cases to abandon a previously implanted lead in favor of a new lead. For example, the previously implanted lead may have become insufficient in its operation and, thus, a new lead is needed. Or, a new lead being different in style or type may be desirable to further the patient's care. In such situations, it is typically common practice to abandon the previously implanted lead in place, rather than explanting the lead, and to install a new, more desirable lead for use in the patient's treatment.
 Generally, an abandoned lead is detached from the electrical therapeutic and/or diagnostic device and the end of
the lead, previously attached to the device, is covered by a lead end cap to prevent body fluids from entering the lead body. If such body fluids are allowed to enter the lead body, an environment may be created that may foster the reproduction and spread of infectious organisms. End caps are generally made of an electrically non-conductive material (e.g., silicone rubber or the like) that serves to minimize the likelihood of low-frequency current flow through the abandoned lead. In certain situations, such low-frequency current flow may result in undesirable stimulation of the body portion to which the lead extends or cause the electrical therapeutic and/or diagnostic device to malfunction, even though the abandoned lead is no longer attached to the device.
 Other advancements in medical technology have led to improved imaging technologies, for example magnetic resonance imaging (MRI). MRI generates cross-sectional images of a human body by using nuclear magnetic resonance (NMR). The MRI process begins with positioning the body to be imaged in a strong, uniform magnetic field, which polarizes the nuclear magnetic moments of protons within hydrogen molecules in the body by forcing their spins into one of two possible orientations. Then an appropriately polarized radio-frequency field, applied at resonant frequency, forces spin transitions between these orientations. The spin transitions create a signal, an NMR phenomenon, which can be detected by a receiving coil.
 Further, shortwave diathermy, microwave diathermy, ultrasound diathermy, and the like have been shown to provide therapeutic benefits to patients, such as to relieve pain, stiffness, and muscle spasms; to reduce joint contractures; to reduce swelling and pain after surgery; to promote wound healing; and the like. Generally, energy (e.g., shortwave energy, microwave energy, ultrasound energy, or the like) is directed into a localized area of the patient's body.
 Traditionally, however, use of these technologies have been discouraged for patients having such implanted medical devices and/or abandoned leads, as the environment produced by the MRI or diathermy apparatuses is generally considered hostile to such implantable medical devices. The energy fields, generated during the MRI or diathermy processes, may induce an electrical current in leads of implantable medical devices and/or in abandoned leads. In conventional leads, whether attached to an electrical therapeutic and/or diagnostic device or abandoned, the electrical current is typically dissipated via the lead's tip electrode into tissue adjacent the distal end of the lead. The dissipation of this electrical current may cause resistive heating in the tissue adjacent the electrode and may result in damage to the tissue in some cases.
 The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.
SUMMARY OF THE INVENTION
 In one aspect of the present invention, an electrical lead end cap is provided. The electrical lead end cap includes a body defining a bore therein capable of receiving and retaining an end of an electrical lead and a connector capable of electrically coupling conductors leading to at least two electrodes.