Long RP′ Tachycardia with an Initial A‐A‐V Activation Sequence: What Is the Mechanism?

Abstract

A 79-year-old man with a history of multiple episodes of paroxysmal supraventricular tachycardia underwent electrophysiologic studies and a catheter ablation procedure. The 12-lead electrocardiogram during tachycardia showed a long RP′ tachycardia with negative P waves in leads II, III, and aVF. No dual anterograde atrioventricular (AV) nodal conduction was elicited by atrial extrastimulation. A narrow QRS tachycardia documented previously was reproducibly induced by atrial extrastimulation (Fig. 1A). During tachycardia, the HA and AH intervals measured 136 and 252 ms, respectively, and the earliest atrial activation was recorded at the ostium of the coronary sinus. Atrial extrastimuli delivered during the tachycardia did not reset the atrial cycle. Atrial overdrive pacing induced a second tachycardia with a similar atrial activation sequence and cycle length, and 2:1AV conduction (Fig. 1B). Ventricular overdrive pacing was delivered at a slightly shorter cycle length than the tachycardia (Fig. 2). Based upon these observations, what is the mechanism of tachycardia?