Patent ID: 7257441

Claim:
An implantable cardioverter defibrillator system for determining and delivering an optimal programmed first-shock strength based on the upper limit of vulnerability, comprising: (a) a plurality of implantable electrodes; (b) a shock delivery subsystem, connected to the electrodes; and (c) a ULV subsystem comprising; i) a sensor, connected to the electrodes, for sensing the electrical activity of the heart, including a change with respect to time of the T-wave of a cardiac signal and including the presence of fibrillation; ii) a timer connected to the sensor for providing a series of shock times, timed relative to a maximum derivative of the T-wave; iii) a test-shock driver, connected to the timer, for transmitting timing and amplitude information regarding T-wave test shocks; iv) a memory unit, connected to the test shock driver and the shock subsystem, for storing programmable values comprising pacing cycle length, timing intervals, an initial shock strength, and values for incrementing and decrementing shock strength; and v) a controller, connected to the sensor, test-shock driver, and shock subsystem for determining the maximum derivative of the T-wave and for incrementally varying shock strength and the shock times; wherein the system provides a test shock having a shock strength and shock time selected by the controller; (d) wherein the controller is programmed to cause: (i) the shock subsystem delivers an initial test shock to the heart at an initial shock strength and an initial shock time; and if the heart does not fibrillate (ii) the system delivers a sequence of test shocks to the heart at the same shock strength and different shock times; and if the heart does not fibrillate (iii) the system decreases the shock strength by a strength decrement and delivers test shocks at a sequence of intervals; and if the heart does not fibrillate (iv) the system repeats steps (d) (i)-(iii) until the heart fibrillates, whereby the shock strength of the test shock immediately prior to the test shock that induces fibrillation represents the upper limit of vulnerability, and whereby the optimal programmed first shock strength of an implantable cardioverter defibrillator system is predicted by a fixed increment in relation to the energy level determined to be the upper limit of vulnerability.