The relation of localized myocardial lesion size to the QRS complex of vectorcardiographic leads

Effects of localized destructive myocardial lesions on the QRS complex of vectorcardiographic leads was studied by graphic derivation of vectors from the detailed activation sequence of the human heart. Lesions of three sizes were postulated at each of 16 cardiac locations and differences between derived vectors in the presence and absence of lesions determined. At each location there was a near linear relation between lesion size and vector differences. Over different locations, however, there were marked variations in the effects of lesions of a particular size. Variations were due to varied activation patterns within each left ventricular wall since the contribution of each wall (anterior, lateral, posterior and septal) to QRS waveform was nearly identical. Findings suggest that the size of extensive destructive lesions will be well represented by the degree of QRS complex change in vectorcardiographic leads but that vectocardiographic estimates of the size of small lesions or of change of size of either small or large lesions are subject to substantial error.