The diagnosis of posterior myocardial infarction

Abstract

An anatomico-pathologic basis for the vectorcardiographic diagnosis of high posterior infarct has been demonstrated. Autopsy findings and vectorcardiographic diagnosis indicate that almost one tenth of all infarcts involving the posterior wall of the left ventricle are small and are limited to its upper portion. Even more common are infarcts so situated but extending to other portions of the left ventricle. The importance of these observations lies in the fact that the high posterior infarcts do not, as a rule, produce diagnostic signs in the electrocardiogram. Consequently, many posterior wall infarcts are overlooked, and in an even larger number of cases the extent of the lesion is minimized. Our preliminary studies in vectorcardiography have directly or indirectly confirmed some generally accepted explanations for the diagnostic failure of the electrocardiogram in cases of infarct and have revealed some new ones. The observations herein reported demonstrate some of the limitations of the electrocardiogram in relation to the diagnosis of posterior infarction. Diagnostic failure is witnessed when the electrocardiogram discloses left bundle branch block, when the posterior infarct is small, located high on the posterior wall, is old, or is associated with acute anterior wall infarction. Old anterior wall infarction and left ventricular hypertrophy do not interfere with the development of the electrocardiographic signs of posterior infarction. It is noteworthy that not a single electrocardiogram in this series of cases was interpreted as normal. An abnormal electrocardiogram, then, obtained in a patient with a clinical picture of acute coronary heart disease, should be considered consistent with, but not diagnostic of, acute infarction. The electrocardiogram was interpreted as abnormal in nineteen of the eighty cases, and in twelve of them anterior infarction was also present. Since acute anterior infarction commonly conceals the electrocardiographic signs of posterior infarct, the latter should be suspected in some cases in which the electrocardiogram shows only acute anterior infarction, especially when changes reciprocal to the anterior infarct are poorly developed or absent and when bundle branch block or high-grade auriculoventricular block appears during the course of the illness. The electrocardiographic changes in high posterior infarct may consist solely of S-T segment depression or tall R and T waves in the precordial leads.