Modulated ventricular parasystole manifesting as apparent Wenckebach exit block

Since Jalife and Moe 1 reported the experimental modulation of a parasystolic focus, it has become evident that a parasystolic rhythm may manifest with features different from those classically described. The modulated parasystolic cycle may become irregular as a result of influence exerted by the sinus beats, and the interectopic intervals may therefore not be mathematically related. 2–5 We present a case of modulated ventricular parasystole in which the typical diagnostic features of parasystole are lacking and in which the distribution of the ectopic beats suggests a Wenckebach form of ectopic-ventricular block.