Spatial velocity of the dynamic vectorcardiographic loop provides crucial insight in ventricular dysfunction.

Abstract

Vectorcardiogram (VCG) represents the trajectory of the tip of cardiac vectors in three dimensional space with varying time. It is a recurring, near-periodic pattern of cardiac dynamics that is constructed by drawing the instantaneous vectors from a zero reference point according to direction, magnitude and polarity in the space. Being a three dimensional entity, it is more informative and more sensitive than conventional ECG as an evaluation tool of the physiology of cardiac dynamics, because of its extra degree of freedom. Accordingly, it is possible to find out even a minute and early electrophysiological alteration in diseases. Each cardiac cycle primarily consists of three loops in VCG corresponding to P, QRS, and T wave activities. The morphological assessment of the QRS loop was carried out in three dimensional space in order to analyze the spatial vectors of the ventricles and their patho-physiological correlation in various cardiac diseases. Spatial Velocity (SV) is a virtual velocity that represents the rate of movement of the tip of the cardiac vector through space, coordinated by three orthogonal leads, and can be estimated by using simple mathematical formula. It is the rate of change in amplitude and the directionality of instantaneous vectors in seriatim in the three dimensional space to quantify their the temporo-spatial characteristic pattern. We propose to evaluate this novel VCG descriptor SV, in normal individuals and patients of ventricular dysfunction. The possible mechanisms consistent with the patho-physiological basis of ventricular dysfunction or heart failure with altered SV would enrich the current understanding of the disease. Heart failure is the final common pathway of multitude of cardiac pathologies. Despite etiological heterogeneity, there are common mechanisms involved in the complex electrophysiological alteration of the failing myocardium. The changes observed as a consequence of ventricular dysfunction involve ion channel remodeling, intercellular uncoupling, myocardial ischemia, alterations in calcium handling, remodeling of the extracellular matrix, the presence of scars, activation of the sympathetic & the renin-angiotensin-aldosterone system, dilatation as well as stretch of viscous etc. The source modulation of the depolarization wave and its propagation in the heart and body fluid volume conductor also influence the visual pattern of cardiac vectors. In addition, patients with heart failure receive pharmacological or non-pharmacological therapies that also influence the electrophysiological changes. We hypothesize that the spatial velocity of ventricular depolarization and repolarization vectors of the VCG loop alters with a characteristic pattern in the patients with ventricular dysfunction and can differentiate healthy individuals from patients with ventricular dysfunction and also differentiate various categories, gradations and severity stratifications of the patients with ventricular dysfunction.