Patent ID: 7890163

Claim:
A cardiac rhythm management system for treating a heart, the system comprising: an implantable medical device configured to be coupled to an implantable lead including a pair of impedance sensing electrodes configured to be placed in the heart to sense a cardiac local impedance signal indicative of a cardiac local wall motion, the implantable medical device including: an impedance sensing circuit adapted to sense the cardiac local impedance signal using the pair of impedance sensing electrodes; and an impedance-based tachyarrhythmia detector adapted to detect a predetermined-type tachyarrhythmia using the cardiac local impedance signal, the impedance-based tachyarrhythmia detector including an impedance-based ventricular fibrillation (VF) detector including: a detection zone generator adapted to produce a VF detection zone specified by one or more threshold amplitudes; and a comparator including a signal input to receive the cardiac local impedance signal, one or more threshold inputs to receive the one or more threshold amplitudes, and an output to indicate a VF detection when the amplitude of the cardiac local impedance signal falls into the VF detection zone.