Planarity of the spatial QRS loop of vectorcardiogram is a crucial diagnostic and prognostic parameter in acute myocardial infarction.

Abstract

Vectorcardiogram (VCG) is a recurring, near-periodic pattern of cardiac dynamics that graphically represents the trajectory of the tip of cardiac vectors in three dimensional space with varying time. VCG is constructed by drawing the instantaneous vectors from a zero reference point according to direction, magnitude and polarity in the space. It is more informative and sensitive than conventional ECG as an evaluation tool of the physiology of cardiac dynamics. Each heart cycle consists of three loops corresponding to P, QRS, and T wave activities in VCG. The morphological assessment of the QRS loop was carried out in order to analyze the spatial vectors of the ventricles and their patho-physiological correlation in various cardiac diseases. It was found that, the three dimensional QRS loop in healthy individuals lies in a plane. It is rather surprising that the normal spatial QRS loop lies in a single plane, considering the complex structure of the ventricular musculature together with the numerous possible pathways along which the depolarization impulse passes. The highly curious phenomenon of planarity of the spatial QRS loop was explained by uniform double layer (UDL) theory, which postulates the phenomenon of activation wave-fronts that propagate with a constant & uniform rate throughout the myocardium. Acute myocardial infarction results in loss of structural and functional integrity of the different layers of heart, perturbation of the uniformity in wave propagation due to the disturbance in directional symmetry, development of nonlinear relationships among the concerned variables, loss of homogeneity and complete loss of planarity of the 3D-QRS loop. The planarity of the 3D-QRS loop is a highly restricted and sensitive parameter and a characteristic feature of normal heart and can be utilized as a test for diagnostic screening of cardiac normalcy and the loss of planarity may be a conspicuous feature of AMI. It will be reasonable to study the morphology of the spatial QRS loop in patients of AMI throughout the course of disease and also in a regular interval through the long-term follow up period. It is expected that with the reperfusion, recovery and salvage of the diseased myocardium; the homogeneity and the intensity of the line density of the membrane current of the UDL would gradually recover with retrieval of the planarity of the spatial QRS loop. The temporal pattern of characteristics alteration of the QRS loop planarity with the natural course of the disease requires intensive evaluation. We propose that, the planarity of the spatial QRS loop, its loss, involution and reversal is a temporal series of events in AMI and also a crucial diagnostic and prognostic parameter.