Selective atrial sensing in dual chamber pacemakers eliminates endless loop tachycardia.

With the introduction of dual chamber pacemakers that have multiple atrial amplitude sensing values, selective P wave sensing is possible. Five consecutive patients were studied who had 1) retrograde atrioventricular conduction, 2) anterograde atrial signals that were at least 1.4 times larger than their corresponding retrograde atrial signals, and 3) dual chamber pulse generators that are capable of discriminating this difference in atrial amplitude. In each patient the pacemaker was programmed in the DDD mode and the postventricular atrial refractory interval was at least 100 ms shorter than the individual's minimal retrograde conduction time. Two atrial sensitivity settings were evaluated in each patient: a high setting to ensure sensing of both anterograde and retrograde P waves, and a lower setting to allow sensing of anterograde P waves only. Ambulatory electrocardiographic monitoring demonstrated that with a high sensitivity setting, each patient sustained endless loop tachycardia (mean number of episodes 41, range 6 to 143) and that a low atrial sensitivity setting eliminated the tachycardia. With the lower atrial sensitivity setting, there was only sporadic atrial undersensing (1.5 episodes for each 1,000 P waves). This study demonstrates that atrial signals having different amplitudes can be selectively sensed. Additionally, dual chamber pulse generators with multiple atrial amplitude sensitivity values can discriminate anterograde from retrograde P waves, ensure anterograde sensing, reject retrograde P waves and eliminate endless loop tachycardia.