Pacing threshold testing induced ventricular fibrillation following acute rate control of atrial fibrillation

A properly placed stimulus on the T-wave during ventricular repolarization can result in ventricular fibrillation (VF). Initiation of VF with pacing on T-wave is a rare event with a few reported cases in the literature. We present a unique case of induced VF attributed to a pacing stimulus on T-wave during ventricular pacing threshold testing of a permanent pacemaker.

A 64-year-old woman with persistent atrial fibrillation (AF) and a permanent pacemaker for tachycardia-bradycardia syndrome presented with symptomatic AF with rapid ventricular response. Acute rate control was achieved with intravenous diltiazem. During ventricular pacing threshold testing, noncapture occurred followed by a pacing spike on T-wave initiating VF. Cardiopulmonary resuscitation and defibrillation converted the rhythm to rate-controlled AF. An acute prolongation of the QT was noted and normalized within 12 hours. No antiarrhythmic medications were used. Postevent laboratory values were within normal limits. She was free of ischemia and an echocardiogram revealed normal left ventricular function. She recovered from the event and was discharged with rate-controlled AF. No further pacing-induced arrhythmias have occurred during follow-up pacemaker interrogation and 12-lead electrocardiograms continued to show normal QT intervals.

Pacemaker-induced VF is an extraordinarily rare complication of cardiac pacing. Alterations in ventricular repolarization with rapid slowing of the heart rate demonstrated by acute prolongation of QT intervals may play a role. This report should alert physicians to the possibility of QT prolongation and an increased risk of ventricular arrhythmias following acute rate control of AF.