INCONSISTENT RESPONSE TO RAPID ATRIAL RHYTHMS IN A DDD PACEMAKER WITHTHE FALLBACK FEATURE

Dual chamber pacing may be problematic in patients with paroxysmal atr ial 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 fall back occurred consistently only when 2xTARP (ms) less than or equal to URL (ms).