Fig 1: A -12 lead ECG showing narrow QRS tachycardia with varying RP interval. B – Electrogram showing the spontaneous initiation of tachycardia. Single atrial impulse has got conducted through both fast and slow pathways to produce 1:2 AV response followed by initiation of tachycardia. His d and His p – His electrograms – distal and proximal, ABL d and P – Ablation catheter distal and proximal, RA 1-10 – Coronary sinus electrograms, RVA d and p – RV electrogram distal and proximal