Fig 2: A – Intracardiac electrogram showing variation in A-A, H-H, H-A and V-V intervals due to decremental conduction in upper common pathway and antegrade slow pathway (S1). B- Electroanatomic map showing dilated coronary sinus ostium (CS-OS) with left SVC (LSVC) and the site of earliest atrial activation (white spot). 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 proxiamal, His po- His potential