Applications of Vectorcardiography for Diagnosis and Risk Stratification in Subpopulations at Risk for Life-Threatening Arrhythmias

Abstract: Introduction: Vectorcardiography, or 3-dimensional electrocardiography is a tool which can be used to identify subtle changes in the electrical forces of the heart, and which can be applied to atrial depolarization, ventricular depolarization and ventricular repolarization for prognostic and diagostic purposes. Methods: Kor’s regression-related and quasi orthogonal methods was used to derive vectorcardiographic parameters from the 12-lead electrocardiogram and applied to a cohort of cryptogenic stroke patients to assess atrial fibrillation, hypertrophic cardiomyopathy patients to assess for ventricular arrhythmias, applied with right-precordial directed quasi orthogonal method to arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVC/D) patients for diagnosis, and applied to ventricular repolarization only to patients with genotype-positive/phenotype-negative Long QT2 syndrome (KNCH2 mutation) to assess for cardiac events. Parametric and non-parameteric parameters were presented as mean ± standard deviation and median (1st to 3rd interquartile ranges). Pearson and Spearman correlation coefficients were used for parametric and non-parametric data, respectively. Odds ratios with univariate and multivariate analyses as well as hazard ratios and Kaplan-Meier curves are presented. P-values under 0.05 were represented as significant. Results: In cryptogenic stroke patients, first atrial fibrillation event was predicted by baseline P-wave duration divided by P-wave vector magnitude (p<0.05). In hypertrophic cardiomyopathy patients, the spatial peaks QRS-T angle differentiated sustained ventricular arrhythmias (VA) from no VA (P < 0.001) and at 124.1 degrees gave positive and negative predictive values and an odds ratio of 36.7%, 96.1%, and 14.2 (95% confidence interval: 3.1-65.6), respectively. Combined right precordial-directed parameters were able to identify ARVD/C patients who otherwise met criteria but did not meet any ECG-specfiic 2010 Taskforce criteria from controls with a positive predictive value of 90.0% and negative predictive value of 83.3%. In patients with genotype positive KCNH2 mutations, without prolongation of the QTc, when dichotomized by the median of 0.30 mV, a low T-wave vector magnitude (TwVM) was associated with elevated cardiac event risk compared to those with high TwVM (HR=2.55, 95%CI 1.07-6.04, p=0.034) and the genotype-negative family members (HR=2.64, 95%CI 1.64-4.24, p<0.001). Conclusion: Vector magnitudes and spatial angles, involving atrial and ventricular depolarization as well as ventricular repolarization, can be helpful in identifying disease as well as first-onset arrhythmia in subpopulations at risk for sudden death or stroke.