Location of myocardial infarcts: A confusion of terms and definitions

Abstract The terminology applicable for describing the location of a myocardial infarct at necropsy is applicable for defining its location by electrocardiogram. Certain terms used primarily electrocardiographically—namely, “inferior,” “diaphragmatic” and “true posterior”—should be avoided because their opposites are not used. Ideally, a proper description of the location of a myocardial infarct should include a definition of its involvement in each of the dimensions of the left ventricle (considered as a cone): the portion of the walls of the circle involved (anterior, posterior, lateral and septal); the amount of the wall's thickness involved (transmural or nontransmural [subendocardial]) and the portions of the wall's length involved (basal half or apical half, or both). Certain portions of the walls of both the left and the right ventricles are rare sites of myocardial infarction, and knowledge of these sites helps in more precisely predicting by electrocardiogram the location of the myocardial infarct. Infarction involving the anterior wall of the left ventricle rarely is limited to just its basal one-half; therefore, anterior myocardial infarction, for practical purposes, indicates involvement of at least the apical half of this ventricle. In contrast, myocardial infarction involving the basal half of the posterior left ventricular wall is common, but the electrocardiogram is not accurate in differentiating posterobasal from posteroapical infarction. Furthermore, the electrocardiogram provides no specific pattern to indicate myocardial infarction of the ventricular septum, the lateral wall of left ventricle, either the posterior or the anterolateral wall of the right ventricle or the papillary muscle. Infarction of the right ventricle virtually never occurs with isolated “anterior” myocardial infarction of the left ventricle. In contrast, nearly 25 percent of patients with “posterior” transmural myocardial infarction also have associated infarction involving at least the posterior wall of the right ventricle.