Electrocardiographic changes of acute lateral wall myocardial infarction: a reappraisal based on scintigraphic localization of the infarct.

To determine how often acute lateral myocardial infarcts may be electrocardiographically "silent," a new approach was utilized in which subjects were selected by admission thallium scintigraphy. Thirty-one patients with their first infarction were identified with moderate to severe perfusion defects of the lateral and posterolateral walls, persistent over 7 days and associated with severe wall motion abnormalities. Patients with involvement of the anterior, septal or "inferior" regions were not included. In nine patients, the perfusion defect extended to the anterolateral wall: all developed ST elevation and Q waves in at least one of the "lateral" leads (I, aVL or V6) but none showed changes in the "inferior" leads (II, III or aVF). In the other 22 patients, the perfusion defect was limited to the lateral and posterolateral walls: only 12 showed ST elevations (inferior leads only in 7, lateral leads only in 2, both leads in 3) and only 9 developed Q waves (inferior in all). In 8 of these 22 patients, the infarct was silent in the sense that no ST segment elevation or Q waves were seen, although ST depressions or T wave inversions, or both, in all but one patient were compatible with subendocardial infarction. The results indicate that the standard electrocardiogram is insensitive to changes in the lateral and posterolateral regions. Additional diagnostic studies are needed for proper localization and sizing of acute myocardial infarcts.