Electrophysiologic delineation of the tachycardia circuit in the slow-slow form of atrioventricular nodal reentrant tachycardia

BackgroundLittle is known about the exact boundaries of the reentrant circuit in the slow-slow form of atrioventricular nodal reentrant tachycardia (AVNRT).ObjectiveThe purpose of this study was to examine the tachycardia circuit in the slow-slow form of AVNRT.MethodsSingle extrastimuli were delivered during the slow-slow form of AVNRT at 10 sites along the right interatrial septum: superior portion of the His-bundle (HB) site, the HB site, three equidistantly divided sites of the AV junction between HB site and coronary sinus ostium (CSOS; sites S, M, and I), and inferior, superior, posterior, posteroinferior, and internal portions of the CSOS in 13 patients. The longest coupling interval of a single extrastimulus that reset the tachycardia and the following return cycle were measured.ResultsThe tachycardia cycle length was 409 ± 50 ms. The earliest atrial electrogram during tachycardia was observed at site I in all patients. The longest coupling intervals at superior-HB, HB site, sites S, M, and I, and inferior-CSOS, superior-CSOS, posterior-CSOS, posteroinferior-CSOS, and internal-CSOS were 340 ± 52, 355 ± 50, 367 ± 50, 378 ± 51, 398 ± 49, 398 ± 52, 355 ± 60, 351 ± 50, 371 ± 48, and 363 ± 54 ms, respectively. The following return cycles were 468 ± 52, 453 ± 52, 442 ± 52, 431 ± 50, 411 ± 52, 410 ± 49, 454 ± 45, 457 ± 57, 438 ± 54, and 445 ± 53 ms, respectively. The longest coupling intervals at site I and inferior-CSOS were significantly longer than those at the other sites (P <.0001). The return cycles at site I and inferior-CSOS did not differ from the tachycardia cycle length, whereas those at the other sites were significantly longer than the tachycardia cycle length (P <.0001).ConclusionSite I and inferior-CSOS are involved in the slow-slow form of AVNRT circuit, and the atrial tissue between those sites form an integral limb of the reentrant circuit.