Fast-Fast form of Atypical AV Nodal Reentrant Tachycardia: Incidence, Electrophysiological Characteristics and Results of Catheter Ablation

Abstract

Background: Both typical and atypical AV nodal reentrant tachycardias (AVNRT) are usually amenable to slow pathway (SP) ablation at the inferoseptal areas. However, rare cases of unusual forms of AVNRT are resistant to SP ablation and their characteristics remain to be elucidated. Methods and Results: Total of 1252 AVNRTs induced in 950 cases were reviewed. Both anterograde and retrograde limbs of tachycardia circuit (TC) were classified into fast pathway (FP) or SP according to the A-H (AHI) and H-A intervals (HAI) during the tachycardia; the anterograde FP (AHI ⁄= 220 msec), and retrograde FP (HAI ⁄= 120 msec). Accordingly, the 1252 AVNRTs were classified into slow-fast (S/F: n=998), slow-slow (S/S: n=119), fast-slow (F/S: n=129) and fast-fast (F/F: n=6) forms. The F/F forms were induced by atrial or ventricular extrastimulation without associated jump-up in the AHI and HAI, and they were characterized by shorter tachycardia cycle length (260±55 msec), short AHI (153±39 msec) and HAI (107±19 msec) during the tachycardia and earliest retrograde atrial activation at the right superoseptum (n=2) or midseptum (n=4). The tachycardias were entrained from the RV and resumed with V-A-V sequence after cessation of entrainment pacing. SP ablation at right inferoseptum was unsuccessful in all F/F forms. Successful ablation was achieved at right superoseptum (n=2) or midseptum (n=4) without creating AV block. Conclusions: F/F forms of AVNRT not involving SP in TC were observed in 0.5% of all AVNRT. It was suggested the TC was smaller and confined to the superior part of AV nodal area in this extremely rare form of AVNRT.