The Electrocardiogram in Acute Myocardial Infarction

to the editor: The review article by Zimetbaum and Josephson (March 6 issue) 1 on the usefulness of the electrocardiogram in the diagnosis of acute myocardial infarction is essential reading for anyone who cares for patients with a suspected acute myocardial infarction. Some qualifications regarding the diagnosis of acute myocardial infarction in patients with left bundle-branch block are in order. Although proposed criteria 2 facilitate the diagnosis, an occasional problem arises when reliance on the criterion of an ST-segment elevation of more than 5.0 mm in leads with primarily negative QRS complexes leads to a false positive diagnosis of acute myocardial infarction. This criterion is nonspecific for acute myocardial infarction, and some patients who have left bundle-branch block without an acute myocardial infarction, but with left ventricular hypertrophy or dilatation, have electrocardiograms with ST-segment elevations that are much larger than 5.0 mm. 3,4 An association between large ST-segment elevations and large QRS complexes has been reported. 3 Repeating electrocardiography may also be of value, since a change in the amplitude of the ST-segment elevation suggests an acute myocardial infarction. 5 Finally, since measurements of ST-segment elevations are being used for the diagnosis of acute myocardial infarction in patients with left bundle-branch block, it is prudent to mark the thorax in order to ensure reproducible serial electrocardiograms. 5