Introduction and objectives: The stimulus-atrial minus ventriculo-atrial interval (SA-VA difference) during ventricular overdrive pacing of a supraventricular tachycardia is used to differentiate atrioventricular reciprocating tachycardia (AVRT) from atrioventricular nodal re-entrant tachycardia (AVNRT), but positive values have always been reported. In atrial tachycardia, the SA conduction is unrelated to the tachycardia mechanism, allowing for negative SA-VA values. We postulated that a negative SA-VA may serve as a criterion for atrial tachycardia in patients with supraventricular tachycardia and ventricular overdrive pacing from the right ventricular apex.

Methods: Multicenter data from ventricular overdrive pacing during atrial tachycardia (from 6 centers) and during AVRT and AVNRT (from 2 centers) were retrospectively and consecutively collected. The correct diagnosis was established using conventional criteria. The SA-VA difference was calculated for each case. The optimal SA-VA cut-off point for the diagnosis of atrial tachycardia was determined.

Results: Out of 240 tachycardias analyzed, ventricular overdrive pacing succeeded in accelerating the atria to the pacing rate without tachycardia termination in 106 cases: 38 (36%) AVNRT, 33 (31%) AVRT, and 35 (33%) atrial tachycardias (all exhibiting long VA intervals). All atrial tachycardias had a negative SA-VA value, while all AVNRT and AVRT cases had positive SA-VA values. A SA-VA value lower than 0 ms was the best cutoff, with an area under the curve of 1 and 100% sensitivity and specificity for the diagnosis of atrial tachycardia.

Conclusions: A negative SA-VA difference is a novel and accurate criterion for the diagnosis of atrial tachycardia with long VA intervals.