Aim: The goal of this study was to compare associations between clinical and ECG predictors of cardiac resynchronization therapy (CRT) response with electrical dyssynchrony. Methods: Body-surface potentials were recorded using a 120-lead system in 4 patients (age 62 ± 12 y, left ventricular ejection fraction (L VEF) 29 ± 5 %; QRS duration 154 ± 19 ms) with post-myocardial infarction scar and left bundle branch block before CRT implantation. A patient-specific heart-torso model derived from MRi with 291 heart-surface nodes was developed. Electrical dyssynchrony index (EDl) was computed as the standard deviation of activation times on the epicardium while uncoupling index (Ul) was measured as the difference between the activation times. Results: QRS duration correlated with mean activation time (r = 0.977; P = 0.023), but did not correlate with EDl or VI. L VEF inversely correlated with activation time at the lowest 20th percentile (r = - 0.960; P = 0.040). Sum absolute QRST integral (SAl QRST), measured on orthogonal XYZ ECG, correlated with EDl (r = 0.955; P = 0.045), and characterized late-activated area of the left ventricle. Conclusion: SAl QRST is a measure of electrical dyssynchrony on ECG.