Ischemia at a distance—So close yet so far

Abstract

ST segment elevation in characteristic electrocardiographic leads during an acute myocardial infarction generally allows correct identification of the coronary artery occluded (1). Electrocardiographic changes, usually ST segment depression, are often noted in other leads, presumably representing myocardium sub served by other coronary arteries. What do such changes mean? Are they a benign electrical phenomenon or a harbinger of trouble ahead? Ekmekci et al. (2) noted that ST segment elevation recorded directly from the anterior epicardial surface after left anterior descending coronary artery ligation in the dog was immediately associated with ST segment depression recorded from the epicardial surface of the posterior left ventricular wall, directly opposite the evolving infarct (Fig. 1). Approximately 15 to 20 minutes later, electrodes from the periphery of the infarct, initially recording mild ST elevation, began recording ST depression as well, with the surrounding normal tissue demonstrating isoelectric ST segments. Hence, ST depression was not only a secondary electrical phenomenon, as evidenced over the posterior wall opposite the infarct, but also a marker of injury or infarction, most likely subendocardial in location, at the margins of the infarct. Nonetheless, the concept that ST depression represented only a secondary or reciprocal change in the presence of an acute myocardial infarction became firmly entrenched in electrocardiographic parlance. Review of hypotheses based on previous clinical studies. Recently there has been renewed interest in the significance of ST segment depression in electrocardiographic leads presumably remote from the zone of the acute infarction. Schuster and Bulkley (3) noted multivessel coronary disease in 20 autopsy patients with postinfarction chest pain associated with electrocardiographic changes (usually ST depression), recorded in leads remote from the zone of the occluded vessel. They coined the phrase ischemia at a