Letters to the Editor: Evaluating patients for CRT, what is relevant: identifying responders or estimating the amount of potential response?

Cardiac resynchronization therapy (CRT) is a very effective therapy for the group of patients with symptomatic heart failure (HF), low ejection fraction and a broad QRS complex. However, it is also very expensive, requires the appropriate team for selection, implantation and intensive follow-up and a substantial amount of individual patients show little improvement. Therefore, identifying the most appropriate candidate for CRT continues to be a challenge in heart failure clinics. Given the existing controversy, it has become clear that the potential benefit for the individual depends on a multitude of factors. First, there is the question whether the underlying substrate, resulting in HF, is amendable with electrical therapy. For this, there has to be some form of (intra-, inter- or atria-ventricular) dyssynchrony (1). Next, the implant procedure and lead placement has to be satisfactory and last, but not least, the myocardium, and the heart as a whole, should not have deteriorated too much and has to be able to improve its function after correcting the underlying electrical problem.