Dual level sensing significantly improves automatic threshold control for R wave sensing in implantable defibrillators. The Angeion Corporation.

ICDs must sense R waves over a range of amplitudes without sensing P or T waves. Automatic threshold control (ATC) is an accepted sensing method for that task. ATC sensing levels are from 25%-75% of the electrogram (EGM) peak, decreasing with an exponential decay. A high sensing level for a time after peak detection may better allow ATC to pass over a T wave, while a lower sensing level thereafter may better allow ATC to sense the next R wave. An ATC was designed with two sensing levels and time constants (tau), using a 58% level (tau = 1.75 s) for 325 ms after peak detection switching to 33% (tau = 1.1 s) thereafter, and was compared to a single level ATC (sensing level = 50%, tau = 1.4 s). The two ATC circuits were tested with 22 arrhythmia EGMs to determine sensitivity and specificity rates at +/-1-, 2-, 5-, 10-, and 20-mV amplitudes. It was confirmed that a dual level ATC significantly improves the sensitivity rate without degrading the high specificity rate of a standard sensing circuit.