Unusual variant of atrioventricular nodal reentrant tachycardia.

Electrophysiologic study in a patient with supraventricular tachycardia revealed an unusual activation pattern in the coronary sinus (CS) electrodes. Pacing maneuvers confirmed the tachycardia was a slow-slow AV nodal reentrant tachycardia with double potentials in the distal CS electrodes due to an earlier left atrial signal (50 ms) and later CS musculature activation. The left-sided AV nodal inputs were successfully ablated from within the CS.