Slow Potential at the Entrance of the Slow Conduction Zone in the Reentry Circuit of a Verapamil‐Sensitive Atrial Tachycardia Originating From the Atrioventricular Annulus

Background Slow conduction zone in a verapamil‐sensitive reentrant atrial tachycardia originating from atrioventricular annulus is composed of calcium channel–dependent tissue. We examined whether there was a slow potential (SP) at the entrance of the slow conduction zone. Methods and Results We first identified the pacing site from where manifest entrainment and orthodromic capture of the earliest atrial activation site were demonstrated in 40 atrioventricular annulus patients with atrioventricular annulus. Radiofrequency energy was then delivered 2 cm proximal to the earliest atrial activation site in the direction of entrainment pacing site and gradually advanced toward the earliest atrial activation site until atrial tachycardia termination to localize the entrance of the slow conduction zone. Electrogram characteristics were analyzed at successful and unsuccessful ablation sites. During sinus rhythm, SP was observed at all 40 successful sites, but was observed at only 12 unsuccessful sites (P<0.0001)...