Inconsistent response to rapid atrial rhythms in a DDD pacemaker with the fallback feature

Dual chamber pacing may be problematic in patients with paroxysmal atrial arrhythmias. The fallback feature has been incorporated into some devices to avoid tracking of rapid atrial rhythms. A case is reported in which the initiation of fallback was inconsistent during paroxysms of atrial flutter. Evaluation of the ventricular output of an isolated device in response to various applied atrial rates revealed that fallback occurred consistently only when 2xTARP (ms) < or = URL (ms).