Initiation and termination of a wide complex tachycardia by an atrial beat

A 28-year-old man with recurrent palpitations and no structural heart disease presented with a documented wide QRS complex tachycardia (WCT). He had a history of slow pathway ablation for atrioventricular (AV) nodal reentrant tachycardia 3 months ago. A standard electrophysiology study was performed using multipolar electrode catheters in the high right atrium, His bundle, right ventricular apex, and coronary sinus. The introduction of atrial extrastimulus from the lateral tricuspid annular region during the tachycardia terminated the tachycardia but recurred after 1 sinus beat (Figure 1). What diagnostic information can be retrieved from the tracing?