Abstract: A system for passively anchoring mid-lead electrodes on an endocardial catheter lead includes at least one fibrosis-anchoring opening positioned along the exterior surface of the catheter lead body proximal or distal to the mid-lead electrodes for passively securing the catheter lead against the interior wall of the heart. Within the fibrosis-anchoring openings a suitable material is provided for anchoring the catheter lead body to the heart wall by fibrosis. Preferably, the fibrosis-anchoring openings comprise at least a pair of openings positioned only partially around the exterior of the catheter lead body at locations both proximal and distal to the mid-lead electrodes, with the catheter lead body between the fibrosis-anchoring openings being preformed to bias the mid-lead electrodes against the heart wall.

Abstract: An amplified, isolated output control circuit is provided for controlling the output switching network of a self-powered defibrillator that delivers a high voltage electrical countershock through a plurality of electrodes. The defibrillator comprises a low voltage battery system, a high voltage capacitor system, a high voltage transformer connected between the battery system and the capacitor system, and an output switching network, such as an H-bridge switching network, connected between the capacitor system and the plurality of electrodes. The defibrillator is controlled by control circuitry that manages the charging and discharging of the electrical countershock and is connected to the output control circuitry. Preferably, the output control circuitry includes an isolated power supply, at least one optoisolator device and at least one amplifier circuit that is powered by the isolated power supply and is connected between the optoisolator device and a switch of the output switching network.

Abstract: A capacitor-discharge implantable cardioverter defibrillator (ICD) has a relatively smaller mass of less than about 120 grams. The smaller mass of the ICD is achieved by selecting and arranging the internal components of the ICD to deliver a maximum defibrillation countershock optimized in terms of a minimum physiologically effective current (I.sub.pe), rather than a minimum defibrillation threshold energy (DFT). As a result of the optimization in terms of a minimum effective current I.sub.pe, there is a significant decrease in the maximum electrical charge energy (E.sub.c) that must be stored by the capacitor of the ICD to less than about 30 Joules, even though a higher safety margin is provided for by the device. Due to this decrease in the maximum E.sub.

Abstract: An improved dual battery power system uses two separate battery power sources for an implantable cardioverter defibrillator, each having optimized characteristics for monitoring functions and for output energy delivery functions, respectively. The monitoring functions are supplied electrical power by a first battery source, such as a conventional pacemaker power source in the form of a lithium iodide battery which is optimized for long life at very low current levels. The output energy delivery functions are supplied by a separate second battery source, such as a pair of lithium vanadium pentoxide batteries, which is optimized for high current drain capability and low self-discharge for long shelf life. The first battery source provides electrical power only to the monitoring functions of the implantable cardioverter defibrillator, and the second battery source provides all of the electrical power for the output energy delivery functions.