Abstract: An implantable cardioverter defibrillator capable of subcutaneous positioning within a patient delivers at least one electrical cardioversion/defibrillation countershocks to the heart of the patient. The implantable cardioverter defibrillator includes a housing, circuitry positioned within the housing to control delivery of the countershocks, and an energy source coupled with the circuitry to provide electrical energy to a capacitor in the circuitry that stores the electrical energy for delivery of the countershocks. Because the circuitry is susceptible to undesirable electromagnetic coupling effects of origin external to the circuitry, particularly the capacitive coupling effects between the circuitry and the housing of the device when at least a portion of the housing is utilized as an electrode, the implantable cardioverter defibrillator also includes a conductive shield, disposed between the housing and the circuitry, to shield the circuitry against such undesired coupling effects.

Abstract: An implantable defibrillator derives a rectangular current waveform from a capacitor discharge by using a current limiter. This pulse-shaping method is equally applicable to single-path and multiple-path situations. A rectangular pulse delivers a maximum of energy for a given peak-field value with a particular electrode combination and pulse duration. Peak field is a measure of the tissue-damage potentiality of a particular discharge.

Abstract: An implantable cardioverter defibrillator includes a battery system and a transformer for selectively charging the capacitor system in response to a cardiac dysrhythmia detected by a sensing system. The system also includes a switching control system for selectively discharging the capacitor system through a plurality of implanted electrodes. The capacitor system has a primary capacitor system connected to the transformer to store a high voltage charge of greater than 1500 volts. A second capacitor system is also provided which is selectively connected to the switching control system. The secondary capacitor system delivers a high voltage output of not more than 1500 volts to the electrodes. A means for selectively connecting the primary capacitor system to the secondary capacitor system and for selectively connecting the secondary capacitor system to the switching control system is also provided.

Abstract: A method and apparatus for controlling an implantable cardioverter defibrillator utilizes a back-biasing precharge circuit to precondition the heart before delivery of a biphasic electrical countershock. The back-biasing precharge circuit delivers a low voltage pulse to the implantable defibrillation electrodes that is opposite to the polarity of the initial phase of the biphasic countershock. In the event of a continuing cardiac arrhythmia which is not successfully converted by a single countershock, subsequent countershocks are delivered having alternating polarities from the preceding countershock such that both the polarity of the back-biasing pulse and the biphasic countershock are reversed as compared to the immediately preceeding countershock.

Abstract: A cardioversion/defibrillation catheter lead has selectively exposable outer conductors that increase the effective electrode area and that can be used to direct electrical countershock vectors delivered by the catheter lead. The lead includes an elongated catheter body having a proximal end, a distal end and a catheter length. The catheter body includes at least one electrical conductor surrounded by a dielectric tubular sheath and an outermost dielectric tubular sheath. Each electrical conductor is electrically connected to an electrical connector located at the proximal end of the catheter body and to a cardioversion/defibrillation electrode located long the catheter body between the proximal end and the distal end. At least a portion of the outermost dielectric tubular sheath includes structure for selectively removing that portion of the outermost tubular sheath, thereby creating an effective length of at least one of the electrodes which is longer than an original length of that electrode.

Abstract: An ICD detection method for sensing the occurrence of an R-wave improves the ability to distinguish R-waves from noise through the use of variable declining sensitivity thresholds. The method includes the consideration of the amplitude of at least the previous most recent R-wave to determine a declining threshold of sensitivity used to recognize a subsequent electrical signal as an R-wave. In the method, the amplitude of the previous R-wave may be classified, based upon amplitude, and based upon the classification, a desirable time constant for the declining threshold of sensitivity is provided as an exponential or reverse exponential decay. Alternatively, a piece wise use of various decay formulas may be combined and used to avoid false recognition of noise as an R-wave.

Abstract: An implantable cardioverter defibrillator (ICD) system features rate-responsive pacing capabilities. An electrical pulse generating device having a housing containing pulse generating circuitry is provided. A conductive lead connectable to the housing that has a first electrode, a second electrode and a coil electrode is provided. Switching circuitry is provided contained in the housing that switches the coil electrode between the rate-responsive sensing electrode to a defibrillation electrode. Control circuity is provided within the housing for controlling the delivery of modulating signals to the coil electrode and for sensing changes in resistance between the coil electrode and the housing. The control circuitry also causes an alteration of the pacing signal applied to the pacing electrode depending upon the change in the resistance sensed.

Abstract: A capacitor-discharge implantable cardioverter defibrillator (ICD) has a relatively longer device life of greater that 5 years. The longer life 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: The present invention is a one piece, disposable pulse generator emulator for emulating a subcutaneous implantable cardioverter defibrillator (ICD) having an active housing electrode. The emulator of the present invention is for use with an external test system to screen a patient for candidacy for an ICD by determining the patient's minimum defibrillation threshold voltage. The one piece, disposable emulator has a housing that has substantially the same conductive geometry as the desired implantable pulse generator.