Type A alternating Wenckebach periodicity in the reentrant pathway of interpolated ventricular extrasystoles

A 67-year-old man with interpolated ventricular extrasystoles is reported in whom alternate sinus QRS complexes were followed by interpolated ventricular extrasystoles with progressively lengthening coupling intervals until one of these alternate sinus complexes failed to be followed by an extrasystole. This is the first report to suggest the presence of type A alternating Wenckebach periodicity in the reentrant pathway of interpolated ventricular extrasystoles. It is suggested that 2:1 block occurred at a proximal level in the reentrant pathway, while Wenckebach block occurred at a distal level in the pathway.