Digital AGC using separate gain control and threshold templating

A system for automatically adjusting a sensing threshold in a cardioverter/defibrillator having a pulse circuit for generating shock pulses based on a detect signal representing cardiac events indicated in electrical activity of a heart, the system comprising:

• an amplifier for amplifying the electrical activity of the heart according to a variable gain;
• a cardiac depolarization detector for detecting depolarizations in the amplified electrical activity of the heart and providing the detect signal representing a cardiac event indicative of a depolarization when the amplified electrical activity exceeds a variable sensing threshold;
• gain controller for adjusting the variable gain of the amplifier based on amplitudes of the amplified electrical activity of at least three detected cardiac events;
• and
• threshold controller for acquiring amplitudes of the amplified electrical activity and for adjusting the variable sensing threshold to a level proportional to the acquired amplitude of the amplified electrical activity of a current detected cardiac event and for decreasing the variable sensing threshold from said level in discrete steps until the variable sensing threshold is at a low threshold value.

A cardiac rhythm management device for generating electrical pulses and coupleable to an electrode for sensing electrical activity of a heart and carrying the electrical pulses to the heart, the device comprising:

• an input/output terminal connectable to the electrode to receive the sensed electrical activity of the heart from the electrode and to provide the electrical pulses to the electrode;
• a sense amplifier coupled to the input/output terminal and amplifying the electrical activity of the heart according to a variable gain;
• a cardiac depolarization detector coupled to the sense amplifier and detecting depolarizations in the amplified electrical activity of the heart and providing a detect signal representing a cardiac event indicative of a depolarization when the amplified electrical activity exceeds a variable sensing threshold;
• gain controller coupled to the sense amplifier and the cardiac depolarization detector to adjust the variable gain of the sense amplifier based on amplitudes of the amplified electrical activity of at least three detected cardiac events;
• and
• threshold controller coupled to the sense amplifier and the cardiac depolarization detector to acquire amplitudes of the amplified electrical activity and to adjust the variable sensing threshold to a level proportional to the acquired amplitude of the amplified electrical activity of a current detected cardiac event and to decrease the variable sensing threshold from the level in discrete steps until the variable sensing threshold is at a low threshold value;
• and
• a pulse circuit coupled to the input/output terminal and the cardiac depolarization detector for generating the electrical pulses based on the detect signal.