Figure1: Surface ECG of narrow complex tachycardia (a) arrhythmia initiation after premature stimulation from HRA with AV prolongation (b) AH and HV interval during tachycardia 47 and 250 msec respectively(c) His synchronous pacing with fusion beat that failed to advance the arrhythmia (d)

Based on observation during electrophysiologic study (EPS), alteration in V-V interval preceded A-A changes with fixed V-A interval. This was against atrial tachycardia.

Due to inability to reset the arrhythmia and considering the existence of decremental properties and arrhythmia induction following AV nodal jump and AH prolongation, the existence of an AP couldn’t be proved.

We proceeded by mapping the earliest retrograde atrial activation using a 4-mm non-irrigated tip ablation catheter. Mapping was initiated from His region and extended to all anticipated areas from parahisian region to tricuspid annulus, posteroseptal TV ring, CS ostium and proximal CS at the roof and base of CS and in middle cardiac vein. The construction of RA activation map failed to reveal earliest activation site. So, we decided to map the left side. Mapping catheter was introduced through femoral artery and advanced retrogradely to the left ventricle (LV). Mapping was started from Aortic cusps then the catheter was pushed down inside LV cavity beneath the Aortic cusps, at the anteroseptal mitral annulus corresponding to Aorto-Mitral continuity (AMC), we recorded the most earliest retrograde atrial activation relative to the aforementioned locations (A-distal CS =50 ms).

Although the above position had the most fused A-V potential, but a distinct isoelectric line could be recorded between A-V potentials. RF energy (30 W) was delivered using an irrigate tip catheter at this site during tachycardia and resulted in termination of tachycardia after few seconds.