Runaway pacemaker with demonstration of supernormal period of excitation

This report documents the presence of supernormal conduction in the normal heart. A 26 yr old woman with congenital heart block treated with a fixed rate permanent pacemaker returned to the hospital with evidence of pacemaker failure. Pacemaker spikes occurred regularly at a rate of 140 per min, eliciting ventricular responses only when they occurred during the supernormal period of the cardiac cycle. Telemetric cardiac monitoring revealed complete pacemaker capture, at a rate of 140 per min when the patient was walking. Following replacement of the pulse generator, the pacemaker performed effectively.