Pseudo-Runaway Pacemaker

Abstract

To the Editor. —Malfunction of a permanent cardiac pacemaker is most often manifested by intermittent or absolute cessation of function or by a reduction from the chronic stable pacing rate. On rare occasions, however, pacemaker tachycardia occurs with rate acceleration up to 100 beats per minute, ie, runaway pacemaker. In this report, pseudo-runaway pacemaker, a previously unrecognized phenomenon, will be presented. Report of Cases.—Case 1. —A 46-year-old woman had a R-wave inhibited demand pacemaker inserted for episodic Stokes-Adams attacks with verified high-degree atrioventricular block. The pacing rate was 72 beats per minute (Figure, A). A routine ECG, taken three months later during an emergency room visit for noncardiac chest pain, showed 100% pacemaker capture at 90 beats per minute (Figure, B). Although the pulse generator was implanted only three months earlier, component failure was suspected, and the unit was replaced. Case 2. —A 70-year-old man had a demand