DUAL LEVEL SENSING SIGNIFICANTLY IMPROVES AUTOMATIC THRESHOLD CONTROLFOR R-WAVE SENSING IN IMPLANTABLE DEFIBRILLATORS

ICDs must sense R waves over a range of amplitudes without sensing P o r T waves. Automatic threshold control (ATC) is an accepted sensing me thod for that task. ATC sensing levels are from 25%-75% of the electro gram (EGM) peak, decreasing with an exponential decay. A high sensing level for a time after peak detection may better allow A TC to pass ov er a T wave, while a lower sensing level thereafter may better allow A TC to sense the next R wave. An ATC was designed with two sensing leve ls and time constants (tau), using a 58% level (tau = 1.75s) for 325 m s after peak detection switching to 33% (tau = 1.1s) thereafter and wa s compared to a single level ATC(sensing level = 50%, tau = 1.4s). The two ATC circuits were tested with 22 arrhythmia EGMs to determine sen sitivity and specificity rates at +/- 1-, 2-, 5-, 10-, and 20-mV ampli tudes. it was confirmed that a dual level ATC significantly improves t he sensitivity rate without degrading the high specificity rate of a s tandard sensing circuit.