Termination of a narrow complex tachycardia by a single extrastimulus: What is the mechanism?

A 49-year-old woman with symptomatic Wolff-Parkinson-White syndrome underwent diagnostic electrophysiological study because of rapid palpitations and ECG-documented narrow complex tachycardia (NCT). Echocardiography was normal. Baseline atrio-His and His-ventricular intervals were 69 ms and 29 ms, respectively. Her clinical tachycardia was induced by rapid ventricular pacing and repeatedly terminated by a single extrastimulus delivered from the distal bipoles of a decapolar catheter (2-5-2 mm spacing) positioned in a posterolateral branch of the coronary sinus (CS) (Figures  1 and 2).
Source: Heart Rhythm - Category: Cardiology Authors: Tags: Unknown of the Month Source Type: research