Unusual demand pacemaker arrhythmia due to partial recycling in the relative refractory period

This report presents the electrocardiograms of a patient with a normally functioning lithium QRS-inhibited pulse generator that exhibited partial recycling with inappropriately short escape intervals. The occurrence of partial recycling was time-dependent rather than voltage-dependent, and was observed only when QRS complexes fell within the relative refractory period of the pulse generator. This resulted in a complex arrhythmia simulating pulse generator malfunction. This observation re-emphasizes the need for the physician to appreciate the technical characteristics of pulse generators to avoid the unnecessary replacement of normally functioning units.