Reflections on EchoCRT: sound guidance on QRS duration and morphology for CRT?

This editorial refers to ‘The effect of QRS duration on cardiac resynchronization therapy in patients with a narrow QRS complex: a subgroup analysis of the EchoCRT Trial’, by J. Steffel et al ., on page doi:10.1093/eurheartj/ehv242. Guidelines give a strong recommendation for cardiac resynchronization therapy (CRT) for selected patients with heart failure.1,2 These recommendations are relatively complex and could be improved and simplified in the light of new data. In this issue of the journal, the EchoCRT investigators show, in a prospective randomized controlled trial, that patients with a QRS duration or <130 ms may be harmed by CRT even if they have evidence of left ventricular dyssynchrony on echocardiography and that this applies similarly to those with a QRS duration of <120 ms and those with QRS 120–130 ms.3 If we knew exactly how CRT worked, then making recommendations on how and in whom it should be used would be easy. However, the precise mechanism(s) by which CRT reduces morbidity and mortality are incompletely understood, which makes targeting the right patients for intervention difficult.4,5 Like many other treatments for heart failure, a single mode of action for CRT seems unlikely and therefore it would be surprising if any single measurement predicted benefit accurately. However, QRS duration certainly helps where many other measures have failed. The mechanisms underlying the effect of CRT probably vary from one patient to the next and, over time, even within an individual patient, because the cardiovascular system is dynamic by design. Potential mechanisms of effect include not only correction of inter- and intraventricular mechanical dyssynchrony, atrioventricular dyssynchrony, and mitral regurgitation, but also long-term effects …