Cardiac resynchronisation therapy (CRT) has been shown to improve functional capacity, quality of life and survival, and to reduce hospitalisations for heart failure [
32]. Although the number of women and men with heart failure is nearly the same, women constituted less than one third of the study population in CRT trials. In the COMPANION and CARE-HF trials, which evaluated the benefits of CRT in patients with moderate to severe heart failure, the hazard ratios for the primary endpoints were very similar [
33,
34]. Some studies, however, have shown greater benefit for women. A meta-analysis of three CRT trials in patients with mild heart failure showed a greater benefit for women [
35]. The main difference occurred in patients with left bundle branch block (LBBB) and a QRS of 130 to 149 milliseconds: women had a significant reduction in heart failure or death and in overall mortality, whereas there was no significant benefit in men. This is an important finding, since guideline recommendations use the same LBBB criteria for patient selection for CRT for women and men. New sex-specific ECG criteria for LBBB have been proposed [
36]. Several confounding factors may explain the better response of female patients: there was a higher proportion of men with ischaemic cardiomyopathy and atrial fibrillation, as well as a smaller percentage of “true” LBBB cases, all factors known to decrease the response to CRT.
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