Figure legends
Figure 1: 12-lead ECG showed a short episode of narrow QRS tachycardia.
Figure 2: VOD during WCT with a cycle length of 286ms and H-V interval of 53ms. Earliest atrial activation was at CS7-8 with H-A interval of 127ms. VOD caused orthodromic His activation with decremental conduction in AV node. The prolongation of A-H contributed to the relative long PPI following the cessation of VOD. After which it turned into a narrow QRS tachycardia with the cycle length, H-V, H-A and atrial activation sequence identical to the WCT. See text for discussion. CS=coronary sinus; VOD=ventricular overdrive pacing; WCT=wide complex tachycardia.