Demonstration of the exact anatomic tachycardia circuit in the fast-slow form of atrioventricular nodal reentrant tachycardia.

BACKGROUND The tachycardia circuit in the fast-slow form of atrioventricular nodal reentrant tachycardia (FS-AVNRT) has not been convincingly defined. METHODS AND RESULTS To define the tachycardia circuit, single extrastimuli were delivered during FS-AVNRT to 9 intra-atrial sites in 12 patients: the His bundle (HB) site; the superior portion of the HB site (S-HB); 3 arbitrarily divided sites on the AV junction extending from the HB site to the coronary sinus ostium (CSOS) (sites S, M, and I); the superior, posterior, and posteroinferior portions of the CSOS (S-CSOS, P-CSOS, and PI-CSOS, respectively); and the CSOS. The inferior portion of coronary sinus ostium (I-CSOS), at which the earliest retrograde activation was observed, was excluded. At each site, the longest coupling interval of the single extrastimulus that reset the tachycardia and the subsequent return cycle was measured. The mean tachycardia cycle length was 370+/-55 ms. The longest coupling intervals at sites S-HB, HB, S, M, I, CSOS, S-CSOS, P-CSOS, and PI-CSOS were 328+/-53, 360+/-55, 358+/-55, 358+/-54, 360+/-55, 338+/-56, 323+/-54, 331+/-56, and 321+/-58 ms, respectively, and the subsequent return cycles were 408+/-58, 371+/-55, 370+/-55, 372+/-56, 370+/-55, 396+/-56, 411+/-60, 405+/-58, and 412+/-59 ms, respectively. The longest coupling intervals at sites HB, S, M, and I were longer than those at S-HB, CSOS, S-CSOS, P-CSOS, and PI-CSOS (P<0.0001). The return cycles at sites HB, S, M, and I did not differ from the tachycardia cycle length, whereas those at CSOS, S-CSOS, P-CSOS, and PI-CSOS were longer than the tachycardia cycle length (P<0.0001). CONCLUSIONS The perinodal atrium extending from the HB site to the I-CSOS is an integral limb of the reentry circuit in FS-AVNRT.