Adjusting the QRS duration by body mass index for prediction of response to cardiac resynchronization therapy: Does one QRS size fit all?

Background: QRS duration (QRSd) is known to be affected by body weight and length. We tested the hypothesis that adjusting the QRSd by body mass index (BMI) may provide individualization for patient selection and improve prediction of cardiac resynchronization therapy (CRT) response. Methods: A total of 125 CRT recipients was analyzed to assess functional (?1 grade reduction in NYHA class) and echocardiographic (?15% reduction in LVESV) response to CRT at 6 months of implantation. Baseline QRSd was adjusted by BMI to create a QRS index (QRSd/BMI) and tested for prediction of CRT response in comparison to QRSd. Results: Overall, 81 patients (65%) responded to CRT volumetrically. The mean QRS index was higher in CRT responders compared to nonresponders (6.2 ± 1.1 vs 5.2 ± 0.8 ms.m2/kg, P < 0.001). There was a positive linear correlation between the QRS index and the change in LVESV (r = 0.487, P < 0.001). Patients with a high QRS index (?5.5 ms.m2/kg, derived from the ROC analysis, AUC = 0.787) compared to those with a prolonged QRSd (?150 ms, AUC = 0.729) had a greater functional (72% vs 28%, P < 0.001) and echocardiographic (80% vs 44%, P < 0.001) improvement at 6 months. QRS index predicted CRT response at regression analysis. Conclusions: Indexing the QRSd by BMI improves patient selection for CRT by eliminating the influence of body weight and length on QRSd. QRS index is a novel indicator that provides promising results for prediction of CRT response.