Differential Diagnosis of Supraventricular Tachycardia with Ventriculoatrial Dissociation during Ventricular Overdrive Pacing

Abstract

Case Presentation A 72-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 long RP’ tachycardia with negative P waves in leads II, III, and aVF. Ventriculoatrial (VA) conduction with a shortest 1:1 pacing cycle length of 780 ms and earliest atrial activation at the ostium of coronary sinus was observed during ventricular overdrive pacing. A narrow QRS tachycardia documented previously was reproducibly induced by programmed atrial, though not ventricular, stimulation. During tachycardia, the His-atrial (HA) and atrial-His (AH) intervals were 381 and 156 ms, respectively. The atrial activation sequence during tachycardia seemed identical to that during ventricular pacing. A 2-mg bolus injection of adenosine triphosphate reproducibly terminated the tachycardia after a last ventricular event, following progressive prolongation of the atrial cycle length. Overdrive ventricular pacing for >30 seconds during tachycardia, at a cycle length 10‐30 ms shorter than the tachycardia cycle length, invariably caused VA dissociation without atrial capture or termination of the tachycardia (Fig. 1). What is the tachycardia mechanism? Comment