Background: Little is known about the exact boundaries of the reentrant circuit in the slow-slow form of atrioventricular nodal reentrant tachycardia (AVNRT).
Objective: The purpose of this study was to examine the tachycardia circuit in the slow-slow form of AVNRT.
Methods: Single 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.
Results: The 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).
Conclusion: Site 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.