Probability and magnitude of response to cardiac resynchronization therapy according to QRS duration and gender in nonischemic cardiomyopathy and LBBB.

QRS morphology and QRS duration (QRSd) determine cardiac resynchronization therapy (CRT) candidate selection but criteria require refinement.To assess CRT effect according to QRSd, treated by dichotomization vs a continuous function, and modulation by gender.Patients selected were those with New York Heart Association class III/IV heart failure and with left bundle branch block and nonischemic cardiomyopathy (to test "pure" CRT effect) with pre- and postimplant echocardiographic evaluations. Positive response was defined as increased left ventricular ejection fraction (LVEF) post-CRT.In 212 patients (LVEF 19% ± 7.1%; QRSd 160 ± 23 ms; 105 (49.5%) women), CRT increased LVEF to 30% ± 15% (P < .001) during a median follow-up of 2 years. Positive response occurred in 150 of 212 (71%) patients. Genders did not differ for QRSd, pharmacotherapy, and comorbidities, but response to CRT among women was greater: incidence 84% (88 of 105) in women vs 58% (62 of 107) in men (P < .001); increase in LVEF 15% ± 14% vs 7.2% ± 13%, respectively (P < .001). Overall, the response rate was 58% when QRSd <150 ms and 76% when QRSd ≥150 ms (P = .009). This probability differed between genders: 86% in women vs 36% in men (P < .001) when QRSd <150 ms and 83% vs 69%, respectively, when QRSd ≥150 ms (P = .05). Thus, female response rates remained high whether QRSd was <150 ms or ≥150 ms (86% vs 83%; P = .77) but differed in men (36% vs 69%; P < .001). With QRSd as a continuum, the CRT-response relationship was nonlinear and significantly different between genders. Female superiority at shorter QRSd inverted with prolongation >180 ms.The QRSd-CRT response relationship in patients with heart failure and with left bundle branch block and nonischemic cardiomyopathy is better described by a sex-specific continuous function and not by dichotomization by 150 ms, which excludes a large proportion of women with potentially favorable outcome.