Abstract 5678: Fast-Fast Form of Atypical AV Nodal Reentrant Tachycardia: Incidence, Electrophysiological Characteristics and Results of Catheter Ablation
Both the typical (slow-fast (S/F)) and atypical (slow-slow (S/S) and fast-slow (F/S)) forms of the AV nodal reentrant tachycardias (AVNRT) are usually amenable to the classical slow pathway (SP) ablation at the inferoseptal atrial region. However, rare cases of unusual forms AVNRT do not involve an SP in the tachycardia circuits (TC), and they are resistant to the classical SP ablation. The characteristics of the atypical AVNRTs not involving an SP in the TCs remain to be elucidated. A total of 1252 AVNRTs induced during the electrophysiological study in 950 cases were analyzed. Both the anterograde and retrograde limbs of the TC were classified into the fast pathway (FP) or SP according to the A-H (AHI) and H-A intervals (HAI) during the tachycardia; the anterograde FP: AHI of <220 ms, anterograde SP: AHI of ≥220 ms, retrograde FP: HAI of <120 ms, and retrograde SP: HAI of ≥120 ms. Accordingly, each tachycardia was classified into one of the S/F, S/S, F/S and fast-fast (F/F) forms. There were 998 S/F forms (79.7%), 119 S/S forms (9.5%), 129 F/S forms (10.3%) and 6 F/F forms (0.5%). The F/F forms were induced by atrial or ventricular extrastimulation without an associated jump-up in the AHI and HAI, and they were characterized by a shorter tachycardia cycle length (260±55 ms), short AHI (153±39 ms) and HAI (107±19 ms) during the tachycardia, earliest retrograde atrial activation (ERAA) at the right superoseptum (n=2) or midseptum (n=4), and 2nd degree AV block without a tachycardia interruption. The retrograde atrial activation sequence during the F/F forms was identical to that during ventricular pacing. The tachycardias could be entrained from the RV, and they resumed with a V-A-V sequence after the cessation of the entrainment pacing. The classical SP ablation at the right inferoseptal region was unsuccessful in all 6 cases with the F/F forms. The successful ablation was achieved at the right superoseptum (n=2) or midseptum (n=4) without creating AV block in all 6 cases. The F/F forms of atypical AVNRT not involving a classical SP in the TC were observed in 0.5% of all AVNRT cases. The results of this study suggested that the TC was smaller and confined to the superior part of the AV nodal area in this extremely rare form of AVNRT.