Probability and Magnitude of Response to Cardiac Resynchronization Therapy According to QRS Duration and Gender in Nonischemic Cardiomyopathy and LBBB

Study Questions:

How do QRS duration (QRSd) and gender modulate the effect of cardiac resynchronization therapy (CRT) in patients with nonischemic cardiomyopathy (NICM) and left bundle branch block (LBBB)?


In this retrospective study, the medical records of patients with NICM, New York Heart Association class III/IV symptoms, LBBB, and with pre- and post-implant echocardiographic examinations were reviewed. A positive response of CRT was defined as an increase in left ventricular ejection fraction (LVEF).


Among the 212 patients (105 [50%] women, QRSd = 160 ms) who underwent CRT, the LVEF increased from a baseline of 19% to 30% (p < 0.001) during a median follow-up of 2 years. Overall, a positive response to CRT was found in 150 of 212 patients (71%). Baseline QRSd (161 vs. 158 ms, p = 0.42) did not differentiate responders from nonresponders. However, when CRT response was gauged with respect to QRSd dichotomized at 150 ms, those with QRSd ≥150 ms were more likely to benefit, as compared to those with QRSd of 120-149 ms (76% [112 of 147] vs. 58% [38 of 65], p = 0.009). Although women were more likely to benefit than men (84% vs. 58%, p < 0.001), their likelihood of benefit was similar whether the QRSd is ≥ or <150 ms (86% vs. 83%; p = 0.77). In men, the likelihood of benefit in those with QRS ≥150 ms and <150 ms was 69% and 36%, respectively (p < 0.001). When the likelihood of CRT benefit was analyzed with respect to QRSd as a continuous function, the relationship was nonlinear and differed significantly between genders.


The authors concluded that in patients with NICM, LBBB, and heart failure, the criterion of 150 ms for the QRSd, although effectively identifying male responders, may exclude a number of female patients who are likely to benefit.


Among patients with LBBB being considered for CRT, the current guidelines give priority to those with a QRSd ≥150 ms (Class I) versus those with QRS <150 ms (Class IIa). This informative study asks us to consider the gender of the patient, and not to withhold this important therapy from women with NICM and LBBB, but in whom the QRSd is <150 ms.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Implantable Devices, EP Basic Science, Acute Heart Failure

Keywords: Cardiac Pacing, Artificial, Cardiomyopathies, Heart Failure, Bundle-Branch Block, Stroke Volume, Medical Records, Cardiac Resynchronization Therapy

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