1) The ECG can be used both before and after cardiac resynchronization therapy (CRT) to select appropriate patients and optimize device programming.
2) Pre-CRT, the ECG helps identify ventricular dyssynchrony and predict response. A wide QRS duration is necessary but not sufficient for a positive response.
3) Post-CRT, the ECG confirms biventricular capture and can predict reverse remodeling based on the degree of QRS narrowing achieved. Optimizing programming using ECG criteria may improve outcomes.