SEPARATE GAIN CONTROL AND THRESHOLD TEMPLATING

A system and method automatically adjusts a sensing threshold in a cardioverter/defibrillator which receives electrical activity of the heart and delivers shock pulses in response thereto. An amplifier amplifies the electrical activity according to a variable gain. A detection circuit detects depolarizations in the amplified electrical activity and provides a detect signal representing a cardiac event indicative of a depolarization when the amplified electrical activity exceeds a variable sensing threshold. Slow gain control circuitry adjusts the variable gain in discrete steps based on stored peak history information representing peak values of the amplified electrical activity. Template generation circuitry responds quickly to set the variable sensing threshold to a level proportional to a peak value of the amplitude of the amplified electrical activity and then decreases the variable sensing threshold from the level in discrete steps until the variable sensing threshold is at a low threshold value.