Diagnosis of Left Anterior Hemiblock in the Presence of Inferior Wall Myocardial Infarction

¹ Division of Cardiology, Department of Medicine, University of Miami School of Medicine; the Veterans Administration Hospital; the Division of Electrophysiology at Jackson Memorial Hospital, Miami, and the Sanatorio Antituberculoso, Maracaibo, Venezuela

Serial recordings were obtained in eight patients with abnormal left axis daviation and acute inferior wall myocardial infarction. The most important electrocardio-graphic finding in four cases in which significant left axis shifts occurred progressively after the infarction was the presence of a Qr pattern in lead II. The corresponding frontal plane vectorcardiogram showed superior orientation of the initial and maximal vectors, clockwise rotation of the QRS loop, and superiorly oriented ST-T loop. These abnormalities were attributed exclusively to the inferior wall necrosis. In contrast, pure left anterior hemiblock was characterized by an rS pattern in lead II, inferior orientation of the initial vectors, leftward and superior deviation of the maximal vector and counterclockwise rotation of the QRS loop. The following changes were seen when left anterior hemiblock coexisted with inferior wall myocardial infarction: (a) QS complexes in lead II; (b) superior orientation of the initial and maximal QRS vectors and (c) counterclockwise rotation of the frontal plane QRS loop. These abnormalities were attributed to the infarction-induced abolishment of the hemiblock-related inferiorly oriented initial vectors, with preservation of the subsequent ventricular activation process. Our knowledge of the electrogenesis of complicated left anterior hemiblock has been enhanced by the analysis of sequential electrocar-diographic and vectorcardiographic changes.