The relation between the pacing sites in the right ventricular outflow tract and QRS morphology in the 12-lead ECG

Optimal pace mapping is a good predictor of the appropriate ablation site for idiopathic right ventricular tachycardia (VT) originating from the right ventricular outflow tract (RVOT). We studied the relationship between the RVOT pacing site and QRS morphology in the 12-lead ECG during pacing to find the optimal site more quickly. In 13 patients with idiopathic VT, pacing at 8 sites in the RVOT (free wall, septum, and anterior and posterior regions of upper and lower sites) was performed while 12-lead ECGs were recorded. The R-wave amplitude minus the S-wave amplitude in lead I (RI-SI) and aVF (RavF-SavF) and the transitional zone index (TZI) were compared in the different pacing sites; TZI was defined to examine the transitional zone as a value. The RI-SI was smaller in the anterior region than in the other regions, and the negative RI-SI predicted that the pacing site was in the upper or lower anterior regions. The RavF-SavF was larger in the septum and anterior regions than in the free wall and posterior regions. The TZI was larger in the free wall region than in the septum. From the results, we constructed a flow chart that differentiates the origin of the arrhythmia in the RVOT and a directional guide that indicates the direction from the current mapping site for optimal pace mapping. The results provided an ECG guide for locating the focus of VT originating from the RVOT. These findings may systematically improve the mapping procedure.