Interruption of cardiac resynchronization therapy by atrial premature complexes

Biotronik devices used for cardiac resynchronization therapy (CRT) combined with defibrillation function (CRT-D) are capable of left ventricular (LV) sensing. Under certain circumstances, LV sensing may cause loss of CRT. The third generation of the Biotronik i-family CRT-Ds enables the recording of event-triggered tracings of the electrogram particularly those involving "CRT pacing interrupt" episodes. We report three cases of a sudden "CRT pacing interrupt" initiated by an atrial premature complex. This was caused by realignment of the LV timing cycles induced by the APCs whereupon LV pacing was inhibited and a self-perpetuating desynchronization process was initiated. In all cases it is the repeated occurrence of LV sensed events that prevents the emission of LV paced events because it displaces the LV upper rate interval from its normal position. Prevention of desynchronization requires programming an LV upper rate faster than the maximum sensor-driven rate or right ventricular upper rate.