QRS Vector Magnitude as Predictor of Ventricular Arrhythmia in Patients With Brugada Syndrome.

Risk stratification is the most challenging part in management of patients with Brugada syndrome (BrS). Conduction delay in the right ventricular outflow tract (RVOT) is the major mechanism underlying ventricular tachyarrhythmia (VTA) in BrS. However, QRS duration was not useful in stratifying high-risk patients in large registries. Reconstructing the traditional 12-lead electrocardiogram into QRS vector magnitude can be used to quantify depolarization dispersion and identify high-risk BrS patients. The aim of the study is to test the significance of the QRSvm as a predictor for VTA in patients with BrS. In this retrospective cohort, we included 136 patients (47 ± 15 years, 66% male) who visited outpatient clinic for cardiogenetic screening. All medical records were examined, all 12- lead electrocardiograms were reconstructed into QRSvm using Kors' quasiorthogonal method and were assessed for the presence of electrocardiographic signs indicative of RVOT conduction delay including R wave sign, deep SI, SII >SIII pattern, and Tzou criteria. QRSvm was significantly lower in patients who either presented with VTA or developed VTA during follow-up (1.24 ± 0.35 vs 1.78 ± 0.42 mV, p < 0.001). Positive RVOT conduction delay signs occurred more frequently in symptomatic patients (20% vs 7%, p < 0.001).The area under receiver operator characteristic curve for QRSvm was 0.85 (95% confidence interval [CI] 0.77 to 0.92). Using QRSvm cutoff of 1.55 mV, sensitivity and specificity were 89% and 71%, respectively. Multivariate regression analysis showed that QRSvm and RVOT signs are independent predictors for VTA in BrS patients (QRS vector magnitude: odds ratio 3.68, 95% CI 2.4 to 6.2, p = 0.001; RVOT: odds ratio 2.6, 95% CI 1.4 to 4.9, p = 0.001). In conclusion, not only electrocardiographic signs indicative of RVOT conduction delay but also QRSvm can be used as a predictor for VTA events in BrS patients.