Unique interaction between an atrial single-chamber pacemaker and a ventricular defibrillator

A well described interaction between an antibradycardia pacemaker and a ven tricular defibrillator is sensing of pacemaker stimuli by the ventricular d efibrillator. This report describes an interaction between an atrial demand pacemaker and a ventricular defibrillator that resulted in ventricular asy stole and polymorphic ventricular tachycardia. In this case, the ventricula r defibrillator sensed atrial pacing stimuli when complete atrioventricular block with a slow ventricular escape rate developed Defibrillator-based ve ntricular demand pacing was inhibited, resulting in prolonged periods of ve ntricular asystole, polymorphic ventricular tachycardia, and multiple defib rillator shocks. Ventricular defibrillator sensing of atrial pacemaker stim uli in the setting of complete atrioventricular block and ventricular asyst ole cannot be simulated during defibrillator implantation when atrioventric ular conduction is intact. Therefore, a pacemaker programmed to atrial dema nd pacing in a patient with a ventricular defibrillator can result in inapp ropriate inhibition of ventricular pacing in the setting of complete heart block. Furthermore, this interaction can be avoided with a dual chamber pac ing ventricular defibrillator.