Prominent R wave in ECG lead V1 predicts improvement of left ventricular ejection fraction after cardiac resynchronization therapy in patients with or without left bundle branch block

Our results highlight the importance of periprocedural ECG analysis to optimize response to CRT. Moreover, patients without left bundle branch block still benefited from CRT if they met our BiV paced morphology criteria. This suggests that postprocedural left ventricular activation as reflected on the ECG may supersede the baseline conduction delay.