Abstract 2647: Analysis of the Anatomical and Electrophysiological Characteristics of Tachycardia Circuit in Atrioventricular Nodal Reentrant Tachycardia Accompanied by the Block in the Upper Common Pathway

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We examined the anatomical and electrophysiological characteristic of the atrioventricular nodal reentrant tachycardia (AVNRT) accompanied by the ventriculo-atrial block during tachycardia, suggesting the presence of upper common pathway in 8 patients. Tachycardia was induced by the atrial burst and/or extrastimulation followed by the AH jump and the earliest atrial electrogram was observed at the His bundle (HB) site in all patients. The HA block was observed after gradual prolongation of the HA interval in 2 patient and abruptly in 6 patients. After administration of isoproterenol, 1:1 HA conduction was resumed in all patients. The tachycardia cycle length, AeHe interval and HeAe interval were 357±89, 275±55 and 80±44 msec, respectively. Single extrastimulus delivered from the HB site reset the tachycardia as soon as it was delivered during late diastole. However, single extrastimulus delivered from the inferior portion of the coronary sinus ostium (I-CSOS) was unable to reset the tachycardia without capturing the earliest atrial electrogram at the HB site, suggesting that atrium is not involved in the circuit. Thus, the longest coupling interval of single extrastimulus that reset the tachycardia at the HB site was significantly longer than that at I-CSOS (347±89 msec vs. 324±109 msec, p=0.012). The following return cycle after extrastimulation at the HB site did not differ from the tachycardia cycle length (357±89 msec, vs. 357±89 msec, p=NS), however, that at I-CSOS was significantly longer than the tachycardia cycle length (398±85 msec, vs. 357±89 msec, p=0.012). Catheter ablation was performed in a stepwise fashion starting at the inferior CSOS. Although the results of single extrastimulation showed that the atrial myocardium at I-CSOS was out of the reentry circuit, ablation near the I-CSOS, distant from HB site, selectively eliminated slow pathway conduction in all patients without impairment of fast pathway conduction. Conclusions: The AVNRT with upper common pathway has the characteristic of relatively long HA interval during tachycardia. Sub-atrial tissue, but not the atrium, extending from the HB site to I-CSOS forms the upper common pathway in AVNRT. It was shown that upper common pathway has an anatomical structure of a certain range.