Unusual resetting of superior-type fast-slow atrioventricular nodal reentrant tachycardia with cycle length alternans by early spontaneous premature ventricular contraction.

The pacing maneuvers for supraventricular tachycardia with cycle length alternans are sometimes difficult, especially when diagnostic ventricular pacing does not conduct to the atrium. Even in such a situation, critical diagnostic findings can be obtained by spontaneous premature ventricular contraction.