Intracardiac electrogram sensing in an arrhythmia control system

An implantable cardioverter/fibrillator device having a sensing system for automatically and rapidly adjusting to changing amplitudes of intracardiac electrogram "ICEG" signals during transitions between normal sinus rhythm and ventricular tachycardia/ventricular fibrillation of a patient's heart, comprising:

• means for sensing and amplifying ICEG signals to generate amplified ICEG signals;
• means for filtering said amplified ICEG signals to remove high frequency and low frequency noise and artifacts therefrom to generate filtered signals;
• means for detecting when levels of said filtered signals cross positive and negative threshold levels and for providing a plurality of corresponding positive and negative detector output signals representative thereof during each heart beat;
• means responsive to said filtered signals for varying said positive and negative threshold levels in accordance with corresponding variations of fractions of the levels of said filtered signals, whereby said positive and negative threshold levels move independently of one another in response to changes in the levels of said filtered signals;
• and
• means for rationalizing said plurality of detector output signals for the generation of only one rationalized output signal per heart beat.