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.
—A 70-year-old man had a demand