Termination of pacemaker endless loop tachycardia by an atrial extrasystole

This article documents the termination of a pacemaker endless loop tachycar dia by a critically timed atrial extrasystole. Although predictable electro physiologically, this mode of termination has not been previously reported. The observation is conceptually important because it provides the final li nk in establishing the similarity of endless loop tachycardia and spontaneo us reentrant AV nodal or junctional tachycardias in terms of initiation and termination by single atrial or ventricular extrasystoles.