Premature ventricular contractions causing sinus arrhythmia and alternating P-R prolongation.

A 68-year-old male patient was referred because of an irregular heart rhythm. The electrocardiogram (Fig. 1) showed sinus bradycardia with interpolated premature ventricular complexes (PVCs) occurring in a trigeminal pattern. There are two interesting observations in Figure 1. First, there is an alternating pattern of P-P intervals, with intervals of 1,320–1,340 ms whenever there is a PVC between two conducted sinus beats and longer P-P intervals of 1,420–1,470 ms when there is not. Secondly, there is also an alternating pattern of P-R intervals, with a P-R interval of 280 ms fol-