Electrophysiological delineation of the tachycardia circuit in atrioventricular nodal reentrant tachycardia.

BACKGROUND The exact boundaries of the reentry circuit in atrioventricular nodal reentrant tachycardia (AVNRT) have not been convincingly defined. METHODS AND RESULTS To define the tachycardia circuit, single extrastimuli were delivered during AVNRT to 8 sites of the right intra-atrial septum: 3 arbitrarily divided sites of the AV junction extending from the His bundle (HB) site to the coronary sinus ostium (CSOS) (sites S, M, and I) and the superior (S-CSOS), inferior (I-CSOS), posterior (P-CSOS), and posteroinferior (PI-CSOS) portions of the CSOS and the CSOS in 18 patients. The mean tachycardia cycle length (TCL) was 368+/-52 ms. Retrograde earliest atrial activation was observed at the HB site in all patients. The longest coupling intervals of single extrastimuli that reset AVNRT at sites S, M, I, I-CSOS, CSOS, S-CSOS, P-CSOS, and PI-CSOS were 356+/-51, 356+/-51, 355+/-52, 357+/-51, 318+/-47, 305+/-53, 311+/-56, and 312+/-56 ms, respectively, and the following return cycles at these sites were 368+/-52, 368+/-53, 367+/-53, 367+/-53, 407+/-66, 431+/-73, 415+/-55, and 412+/-56 ms, respectively. The longest coupling intervals at sites S, M, I, and I-CSOS did not differ from each other and were longer than those at CSOS and S-, P-, and PI-CSOS (P<0.0001). The return cycles at sites S, M, I, and I-CSOS did not differ from the TCL, whereas those at CSOS and S-, P-, and PI-CSOS were longer than the TCL (P<0.0001). CONCLUSIONS The perinodal atrium extending from the HB site to I-CSOS was involved in the tachycardia circuit. I-CSOS was thought to be the entrance of the slow pathway.