Vectorcardiographic study of the QRS loop in patients with left anterior focal block

Abstract

The authors have studied the vectorcardiograms of 40 patients, 45 years of age or over, whose electrocardiograms showed a QRS duration shorter than 120 msec., a leftward shift of the mean QRS axis and ventricular complexes with a tall R wave in Leads I and aV L, and an rS morphology in Leads II, III, and aV F. Most patients had atherosclerosis, hypertension, or ischemic heart disease. The following vectorcardiographic characteristics were disclosed: (1) The frontal plane loop was open-faced and turned counterclockwise in all cases; (2) the initial vectors were nearly always directed anteriorly and inferiorly; (3) the early vectors travelled horizontally to the left and, to a variable extent, posteriorly; (4) the midtemporal vectors were located in the left, posterior, and superior octant. These vectorcardiographic features were sometimes observed to be transitory or intermittent or to precede the development of a complete left bundle branch block. Their association with a complete right bundle branch block is known to be a common forerunner of complete atrioventricular block. From comparison with experimental data reported in the literature, the characters of the loops observed in these cases are assumed to be related to a delayed activation of the anterolateral wall of the left ventricle and to correspond to left anterior focal block.