Ventricular asystole due to inhibition of ventricular backup pacing by a dual chamber pacemaker: possible pitfalls of default settings

Abstract

A 62-year-old patient presented with dizzy spells after her dual chamber pacemaker (Medtronic Enrhythm P1501DR), implanted for complete AV block, had been reprogrammed to deliver antitachycardia therapy (ATP) for paroxysmal atrial tachycardia. Her symptoms were caused by inhibition of ventricular backup pacing during ATP, leading to ventricular asystoles. Inhibition was the result of premature ventricular beats occurring prior to ATP: when ventricular backup pacing is left in the default setting, this pacemaker withholds backup pacing if any of the four preceding events is a sensed event. This case illustrates the possibly hazardous effects of default pacemaker settings, especially in pacemaker-dependent patients. (Neth Heart J 2010;18:323-6.) Keywords: Cardiac Pacing; Arrhythmias; Pacemaker; Ventricular Function W hen implanting and programming a pacemaker, the default settings of the specific pacemaker type should be known to the cardiologist and pacemaker technician, and possible risks of these settings in an individual patient should be considered. We present a case that illustrates how unawareness of the exact default settings of a pacemaker can be hazardous to a patient. case A 62-year-old female patient with a medical history of hypertension and paroxysmal atrial fibrillation presented to the emergency department with haemodynamic instability due to viral myocarditis complicated by complete atrioventricular block. She was successfully resuscitated and a temporary transvenous ventricular pacing electrode was inserted. After the patient recuperated, a Medtronic Enrhythm P1501DR dual chamber pacemaker was implanted. During follow-up, pacemaker interrogation showed that the patient remained completely pacemaker-dependent. Frequent paroxysms of atrial tachycardia were recorded by the pacemaker, with a good response to oral amiodarone. Unfortunately, amiodarone had to be discontinued because of side effects. At the next check-up several months later, pacemaker diagnostics revealed long episodes of atrial tachycardia, leading to frequent mode switches of the pacemaker to DDI mode. A sustained atrial tachycardia was terminated at the outpatient clinic by using the pacemaker's manual antitachycardia pacing function. AT/AF detection and therapy settings were programmed to 'On', so that termination of new episodes of atrial tachycardia by antitachycardia pacing (ATP) could be attempted. The pacemaker was programmed to classify a supraventricular rate of >133 beats per minute as AT/AF. A ramp of 20 atrial stimuli was programmed to be delivered one minute after detection of atrial tachycardia. This relatively long ramp sequence (the nominal value is six stimuli per ramp sequence) was chosen because the sustained atrial tachycardia mentioned before had not responded to ramp sequences of less than 20 stimuli. The initial ramp stimulus was to be delivered after an interval of 94% of the detected A-A interval, with an interval decrement of 10 msec for subsequent stimuli and a minimum stimulus interval of 150 msec. If nece...