Vectorcardiographic QRS area is associated with long-term outcome after cardiac resynchronization therapy

Background: Recent studies have suggested that vectorcardiographic measures predict left ventricular (LV) reverse remodeling and clinical outcome in patients receiving cardiac resynchronization therapy (CRT). Objectives: The objectives of this study were to compare predictive abilities of different vectorcardiographic measures (QRS area and sum absolute QRS-T integral) and transformation methods (Kors and inverse Dower) and to assess the independent association between the best predictor and outcomes in CRT recipients. Methods: This retrospective study included CRT recipients with a digital baseline electrocardiogram, QRS duration ≥120 ms, and ejection fraction ≤35%. The end point was a composite of heart transplantation, LV assist device implantation, or all-cause death. Analyses were performed for the overall cohort and for a prespecified subgroup of patients with left bundle branch block (LBBB). Results: Of 705 included patients with a mean age of 66.6 ± 11.5 years, 492 (70%) were men, 374 (53%) had ischemic heart disease, and 465 (66%) had LBBB. QRS area from vectorcardiograms derived via the Kors transformation demonstrated the best predictive value. In multivariable Cox regression, patients with a smaller QRS area (≤ 95 μVs) had an increased hazard in the overall cohort (adjusted hazard ratio 1.65; 95% CI 1.25-2.18 P <.001) and in the LBBB subgroup (adjusted hazard ratio 1.95; 95% CI 1.38-2.76 P <.001). QRS area was associated with outcome in patients with QRS duration <150 ms (unadjusted hazard ratio 3.85; 95% CI 2.02-7.37 P <.001) and in patients with QRS duration ≥150 ms (unadjusted hazard ratio 1.76; 95% CI 1.32-2.34 P <.001). Conclusion: Vectorcardiographic QRS area is associated with survival free from heart transplantation and LV assist device implantation in CRT recipients.