Usefulness of interatrial conduction time to distinguish between focal atrial tachyarrhythmias originating from the superior vena cava and the right superior pulmonary vein

Objective: Differentiation of the tachycardia originating from the superior vena cava (SVC) or the right superior pulmonary vein (RSPV) is limited by the similar surface P‐wave morphology and intraatrial activation pattern during tachycardia. We sought to find a simple method to distinguish between the two tachycardias by analyzing the interatrial conduction time. Methods: Sixteen consecutive patients consisting of 8 with SVC tachycardia and the other 8 with RSPV tachycardia were studied. The interatrial conduction time from the high right atrium (HRA) to the distal coronary sinus (DCS) and the intraatrial conduction time from the HRA to the atrial electrogram at the His bundle region (HIS) were measured during the sinus beat (SR) and during the tachycardia‐triggering ectopic atrial premature beat (APB). The differences of interatrial (Δ[HRA‐DCS]_SR‐APB) and intraatrial (Δ[HRA‐HIS]_SR‐APB) conduction time between SR and APB were then obtained. Results: The mean Δ[HRA‐DCS]_SR‐APB was 1.0 ± 5.2 ms (95% confident interval [CI]–3.3–5.3 ms) in SVC tachycardia and 38.5 ± 8.8 ms (95% CI 31.1–45.9 ms) in RSPV tachycardia. The mean Δ[HRA‐HIS]_SR‐APB was 1.5 ± 5.3 ms (95% CI –2.9–5.9 ms) in SVC tachycardia and 19.9 ± 12.0 ms (95% CI 9.9–29.9 ms) in RSPV tachycardia. The difference of Δ[HRA‐DCS]_SR‐APB between SVC and RSPV tachycardias was wider than that of Δ[HRA‐HIS]_SR‐APB (37.5 ± 9.3 ms vs. 18.4 ± 15.4 ms, P < 0.01). Conclusions: The wide difference of the interatrial conduction time Δ[HRA‐DCS]_SR‐APB between SVC and RSPV tachycardias is a useful parameter to distinguish the two tachycardias and may avoid unnecessary atrial transseptal puncture.