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Abstract: Introduction: CRT had become a standard of treatment for patients with drug refractory heart failure. The presence of many cases of non-responders raises the need for device optimization echocardiography that is an established tool used to optimize CRT programming, but it is time-consuming. It was not yet defined whether a QRS width-based strategy may be a helpful tool for device programming. Aim of study: The aim of this study is to compare the optimal interventricular delay interval (V–V interval) obtained by echo with that obtained by a simpler method using QRS width in surface ECG. Methods and results: Twenty patients with implanted CRT were enrolled. All patients underwent echocardiographic optimization of the (A–V interval) after which five different V–V intervals (LV+30, LV+60, RV+30, RV+60, L+R0) were compared measuring Left Ventricular Outflow Tract Velocity Time Integral (LVOT VTI) as a surrogate for ejection fraction. A 12-lead ECG was recorded and QRS duration was measured in the lead with the greatest QRS width. The ECG optimized V–V interval was defined according to the narrowest achievable QRS interval among the 5 V–V intervals. The echocardiographic-optimized V–V interval was defined according to the highest LVOT VTI among the 5 V–V intervals. The echocardiographic-optimized V–V interval was left ventricle+30ms in 2 patients (10%), left ventricle+60ms in 8 pts (40%), simultaneous pacing in 8 pts (40%) and right ventricle+30ms in 2 pts (10%). ECG method (using QRS width), had 85% coincidence with the echocardiographic method (using LVOT VTI) (κ =0.906), (r =0.81 P <0.001). Conclusion: Significant correlation appeared to exist during optimization of CRT between VV programming based on the shortest QRS interval at 12-lead ECG pacing and that based on highest LVOT VTI by echocardiography. A combined ECG and echocardiographic approach could be a more convenient solution in performing V–V optimization. [Copyright &y& Elsevier]