Cardiac-Resynchronization Therapy in Heart Failure with a Narrow Qrs Complex

Despite recent advances, heart failure remains a common cause of death and morbidity. According to current guidelines, cardiac-resynchronization therapy (CRT) is indicated for patients receiving stable medical therapy recommended by current guidelines who have moderate-to-severe heart failure, a left ventricular ejection fraction of 35% or less, and a QRS duration of 120 msec or more as assessed electrocardiographically.1 However, many patients with heart failure have a QRS duration of less than 120 msec,2 and it is currently not recommended that they receive CRT. Up to 50% of these patients show echocardiographic evidence of ventricular dyssynchrony3,4 and hence might benefit from CRT.

Single-center studies have suggested that dyssynchrony criteria that are based on echocardiographic measurements can identify patients who can benefit from CRT,5-7 resulting in frequent off-label use of CRT in patients with a narrow QRS complex.8 Small, randomized clinical studies that were not powered to assess clinically relevant outcomes9-14 have suggested the existence of true clinical equipoise, thereby setting the stage for a definitive outcome trial. We therefore initiated the Echocardiography Guided Cardiac Resynchronization Therapy (EchoCRT) study to investigate the effect of CRT on morbidity and mortality among patients with symptomatic heart failure, a narrow QRS complex, and echocardiographic evidence of left ventricular dyssynchrony.

METHODS

Study Design and Oversight

The EchoCRT study was an investigator-initiated, international, multicenter, randomized clinical trial. The trial was designed by the executive committee (see the Supplementary Appendix, available with the full text of this article at NEJM.org) and sponsored by Biotronik, with support for echocardiographic training and software provided by GE Healthcare. Biotronik was responsible for trial execution and monitoring. The