| Sumario: | Background: Several studies have evaluated the role of QRS duration (QRSd) or QRS narrowing as a predictor of response to cardiac resynchronization therapy (CRT) to reduce nonresponders. Aim: Our study aimed to determine the correlation between the relative change in QRS index (QI) compared to clinical outcome and prognosis in patients who underwent CRT implantation. Methods: A three‐centers study involving 398 patients with a CRT device was conducted. Clinical, echocardiographic and pharmacological variables, QRSd before and after CRT implantation and QI were measured. Results: In a 6‐month follow‐up, a significant improvement in left ventricular ejection fraction (LVEF), left ventricular end‐diastolic and systolic volumes (LVEDV and LVESV) were observed. QI was related to reverse remodeling (multiple r‐squared: 0.48, adjusted r‐squared: 0.43, p =.001), and the cut‐off value that best predicted LV reverse remodeling after 6 months of CRT was 12.25% (AUC 0.7, p =.001). At 24 months, a statistically significant difference was found between patients with a QI ≤ 12.25% and those with a QI > 12.25% regarding NYHA class worsening (p =.04). The mean of the QI of patients who died from cardiovascular causes was lower than patients who died of other causes (p =.0179). A correlation between pre‐CRT QRSd/LVEDV and QI was observed (r = + 0.20; p =.0003). A higher QRSd/LVEDV ratio was associated with an improved LVEF, LVEDV, and LVESV (p <.0001) at follow‐up. Conclusions: QI narrowing after CRT was related to greater echocardiographic reverse remodeling and a lower rate of adverse events (death or cardiovascular hospitalizations). The QI can improve the prediction of adverse events in a population with CRT regardless of comorbidities according to the Charlson Comorbidity Index. QI could be used to predict CRT response.
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