The interpretation of gross left axis deviation in the electrocardiogram.

In 94 patients with prominent left axis deviation, there was a marked disparity in the mean angles determined by the maximum magnitude of the deflections and that determined by areas. There was also considerable variation in the angle of the maximum vector in the frontal plane (frontal plane angle) and the angle of 50 msec vector in the frontal plane. Similar results were observed in 17 cases of ostium primum atrial septal defect. These differences contrasted with the findings in a normal group of 50 subjects where a close correlation was found. The initial vector was directed to the right in approximately 80% of normals and 60% of the patients with LAD indicative of conduction defects in the left anterior fascicular or its distal ramifications. We conclude that a rightward orientation of the 5--10 msec vector (i.e. causing a Q wave in lead 1) should not be required for diagnosis of left anterior fascicular block. The spatial orientation of the initial vector was always anterior in the control subjects. In these 'normals', as well as in the patients with left axis deviation, the initial vector varied markedly in its azimuth direction (right or left) when superiorly directed; but when inferiorly directed in the normal subjects it was virtually always directed rightward. From these data we were unable to construct rigid criteria which would reliably distinguish aberrant excitation patterns manifested by gross left axis deviation in the electrocardiograms of patients with established heart disease from subjects without defined heart disease. Old infarction patterns, anterior, inferior, and lateral were not obscured by the associated anterior fascicular block.