Cardiac resynchronization therapy in patients with a narrow QRS.

Although cardiac resynchronization therapy (CRT) is indicated in patients with moderate to severe heart failure with a wide QRS complex (> 120 ms), current guidelines exclude many heart failure patients with a narrow QRS. Detecting mechanical dyssynchrony on echocardiography has become a promising tool in selecting patients with a narrow QRS who may respond to CRT. Several small single-center studies identified patients with a narrow QRS (using echocardiography-based dyssynchrony criteria) who responded favorably to CRT; however, the results of two recent pilot studies remain elusive. The results of the RethinQ study do not provide necessary evidence for making clinical treatment decisions in this population. The lack of definitive evidence is the strongest rationale for conducting an adequately powered, long-term, end point-driven, randomized controlled trial to investigate whether CRT therapy can improve morbidity and mortality outcomes in heart failure patients with a narrow QRS. Such a trial, the EchoCRT trial, has recently been launched.