Termination of pacemaker endless loop tachycardia by an atrial extrasystole.

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