Recurrent tachyarrhythmia associated with a bifocal demand pacemaker.

A recurrent tachyarrhythmia complicated the course of a patient with a permanent atrioventricular sequential (bifocal) demand pacemaker. Investigation by intracardiac electrocardiographic studies revealed that the arrhythmia was associated with normally functioning bifocal pacemaker, whose atrioventricular sequential interval approximated the patient's conduction time from atrium to ventricle. The mechanism of initiation and conversion of the arrhythmia was elucidated. Appreciation of this arrhythmia is necessary for appropriate clinical use of a bifocal demand pacemaker.