Cardiac resynchronization therapy: back to ECG?

In recent years, considerable effort has been devoted to improving patient selection and the programming of cardiac resynchronization therapy (CRT). Mechanical dyssynchrony has been investigated through echocardiography and the reliability of ECG in selecting patients has been criticized and doubt has been cast on its role. Up to now, patient selection for CRT has relied upon the criteria of a prolonged QRS, evidence of the electrical impairment of the conduction system. Can we get more information from ECG morphology? Can it provide any marker for selecting candidates to CRT? Can we obtain useful information from the paced ECG morphology by analysis of fusion beats? Can we use ECG to optimize biventricular or single-site left ventricular pacing programming? The present review provides a critical analysis of the criteria for patient selection and the methods for optimal device setting, all based on 12-lead ECG morphology.