Analysis of speed, curvature, planarity and frequency characteristics of heart vector movement to evaluate the electrophysiological substrate associated with ventricular tachycardia

Background: We developed a novel method of assessing ventricular conduction using the surface ECG. Methods: Orthogonal ECGs of 81 healthy controls (age 39.0±14.2 y; 51.8% males; 94% white), were compared with iDower-transformed 12-lead ECGs (both 1000. Hz), recorded in 8 patients with infarct-cardiomyopathy and sustained monomorphic ventricular tachycardia (VT) (age 68.0±7.8. y, 37.5% male, mean LVEF 29±12%). Normalized speed at 10 QRS segments was calculated as the distance traveled by the heart vector along the QRS loop in three-dimensional space, divided by 1/10th of the QRS duration. Curvature was calculated as the magnitude of the derivative of the QRS loop tangent vector divided by speed. Planarity was calculated as the mean of the dihedral angles between 2 consecutive planes for all planes generated for the median beat. Orbital frequency (a scalar measure of rotation rate of the QRS vector) was calculated as a product of speed and curvature. Results: Mixed regression analysis showed that speed was slower [6.6 (95%CI 4.4-8.9) vs. 24.6 (95%CI 11.5-37.7)V/ms; P<0.0001]; orbital frequency was smaller [1.4 (95%CI 1.2-1.6) vs. 6.8 (95%CI 5.4-8.1)ms^-1; P<0.0001], and planarity was larger by 3.6° (95%CI 1.4°-5.8; P=0.002) in VT cases than in healthy controls. ROC AUC for orbital frequency was 0.940 (95%CI 0.935-0.944) across all frequencies and QRS segments. ROC AUC for planarity at 70-249Hz was 0.995 (95%CI 0.985-1.00). ROC AUC for speed at 70-79Hz was 0.979 (95%CI 0.969-0.989). Conclusion: This novel method reveals characteristic features of an abnormal electrophysiological substrate associated with VT.