The improvement in the arithmetic value of the two comparison metrics will be tested as the site of pacing approaches the site of earliest ventricular activation (Groups A&B) or virtual VT exit sites in group C or the index pacing site (in group D). The best CORR and RMSE between the BSPM obtained during VT (in group A and B)/virtual VT exit sites (in group C) or index pacing site (group D) and different pacing sites (including successful and unsuccessful ablation sites) will be recorded. A simple linear regression will be used to compare the CORR and RMSE difference at each pacing site to distance between this pacing site and the successful ablation site as a surrogate of the best pace-match (in group A and B) or the corresponding virtual VT exit site (in group C) or index pacing site (group D). P value <0.05 will be considered significant. The mean sensitivity, specificity, and positive- and negative-predictive accuracies of the arithmetic metrics in determining the VT origin/exit site will be determined. We will repeat the previous protocol using different ECG subsets including 12 lead ECGs and X, Y and Z leads. The predictive accuracies for different subsets of electrodes will be measured and compared to those derived from using the whole BSPM obtained from the 120 ECG leads.