Vectorcardiographic QRS area as a novel predictor of response to cardiac resynchronization therapy

- The best definition for predicting CRT response includes mid-QRS notching in ≥ 2 leads contiguous leads of V1, V2, V5, V6, I and aVL.
- Such LBBB definition improves the selection of patients that respond to CRT by a factor of 4 compared to using QRS duration > 150 ms and by a factor 2 as compared to conventional LBBB definitions.
- Selection of CRT candidates with good response is at least as good with the objective and direction insensitive QRSAREA, derived from the VCG.
- 3D VCG is a promising tool for better application of CRT.

BackgroundQRS duration and left bundle branch block (LBBB) morphology are used to select patients for cardiac resynchronization therapy (CRT). We investigated whether the area of the QRS complex (QRSAREA) on the 3-dimensional vectorcardiogram (VCG) can improve patient selection.MethodsVCG (Frank orthogonal lead system) was recorded prior to CRT device implantation in 81 consecutive patients. VCG parameters, including QRSAREA, were assessed, and compared to QRS duration and morphology. Three LBBB definitions were used, differing in requirement of mid-QRS notching. Responders to CRT (CRT-R) were defined as patients with ≥ 15% reduction in left ventricular end systolic volume after 6 months of CRT.ResultsFifty-seven patients (70%) were CRT-R. QRSAREA was larger in CRT-R than in CRT non-responders (140 ± 42 vs 100 ± 40 μVs, p < 0.001) and predicted CRT response better than QRS duration (AUC 0.78 vs 0.62, p = 0.030). With a 98 μVs cutoff value, QRSAREA identified CRT-R with an odds ratio (OR) of 10.2 and a 95% confidence interval (CI) of 3.4 to 31.1. This OR was higher than that for QRS duration > 156 ms (OR = 2.5; 95% CI 0.9 to 6.6), conventional LBBB classification (OR = 5.5; 95% CI 0.9 to 32.4) or LBBB classification according to American guidelines (OR = 4.5; 95% CI 1.6 to 12.6) or Strauss (OR = 10.0; 95% CI 3.2 to 31.1).ConclusionQRSAREA is an objective electrophysiological predictor of CRT response that performs at least as good as the most refined definition of LBBB.Condensed abstractIn 81 candidates for cardiac resynchronization therapy (CRT) we measured the area of the QRS complex (QRSAREA) using 3-dimensional vectorcardiography. QRSAREA was larger in echocardiographic responders than in non-responders and predicted CRT response better than QRS duration and than simple LBBB criteria. QRSAREA is a promising electrophysiological predictor of CRT response.