Pitfalls of Atrial Advancement Using a Ventricular Extra-stimulus During Supraventricular Tachycardia

The differentiation of the retrograde conduction pathway is essential for the diagnosis of paroxysmal supra ventricular tachycardia (PSVT). An eccentric retrograde atrial activation sequence during the tachycardia could give rise to a diagnosis of accessory pathway (AP) conduction. However, in the case of PSVT, which exhibits a concentric retrograde atrial activation sequence, it is confusing to identify whether the retrograde conduction pathway is through the atrioventricular (AV) node or via an AP. Pacing maneuvers are needed to differentiate the retrograde conduction pathway during the tachycardia. The most common pacing maneuver used to identify AP conduction is the delivery of a single His-refractory ventricular extra-stimulus (VES) during the tachycardia. The main pitfall of this maneuver is the distance from the remote pacing site to the AP, such as a VES from the right ventricular (RV) apex to the left lateral AP. A remote pacing site will not be able to pre-excite the ventricular myocardium near the AP, and as a result, the AP conduction will not be manifested. However, despite the relatively short distance, this pitfall arose in our case and involved a VES from the RV apex to the right antero-septal AP. With this case report, we would like to propose a hypothetical mechanism to explain this finding.