Quantitative Assessment of Vectorcardiographic Loop Morphology

• Fragmented QRS has low sensitivity for detection of QRS loop folding
• Circular statistic of the normal vector of main QRS loop plane is reported
• Value of the dynamic of the dihedral and rotational angles throughout the QRS loop

Vectorcardiography (VCG), developed 100 years ago, characterizes clinically important electrophysiological properties of the heart. In this study, VCG QRS loop roundness, planarity, thickness, rotational angle, and dihedral angle were measured in 81 healthy control subjects (39.0 ± 14.2y; 51.8% male; 94% white), and 8 patients with infarct-cardiomyopathy and sustained monomorphic ventricular tachycardia (VT) (68.0 ± 7.8y, 37.5% male). The angle between two consecutive QRS vectors was defined as the rotational angle, while dihedral angle quantified planar alteration over the QRS loop. In VT subjects, planarity index decreased (0.63 ± 0.22 vs. 0.88 ± 0.10; P = 0.014), and dihedral angle was significantly more variable (variance of dihedral angle, median (IQR): 897(575–1450) vs. 542(343–773); P = 0.029; rMSSD: 47.7 ± 12.7 vs. 35.1 ± 13.1; P = 0.027). Abnormal electrophysiological substrate in VT patients is characterized by the appearance of QRS loop folding, likely due to local conduction block. The presence of fragmented QRS complexes on the 12-lead ECG had low sensitivity (31%) for detecting QRS loop folding on the VCG.

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