Termination of an unusual long RP tachycardia: What is the mechanism?

A 36-year-old woman underwent a diagnostic electrophysiology study because of rapid palpitations and KardiaPro (AliveCor, Mountain View, CA) documented supraventricular tachycardia unresponsive to metoprolol therapy. She denied syncope. Her 12-lead electrocardiogram was normal. Baseline atrio-His and His-ventricular intervals measured 48 and 42 ms, respectively. Programmed atrial extrastimulation using single atrial extrastimuli repeatedly induced her supraventricular tachycardia (Figure  1). The response to ventricular overdrive pacing is shown in Figure 2.
Source: Heart Rhythm - Category: Cardiology Authors: Tags: Unknown of the Month Source Type: research