Coronary Thrombosis and Fatal Myocardial Ischemia

IN RECENT years the role of coronary thrombosis as a precipitating cause of acute myocardial infarction (AMI) has been questioned. "Which comes first, coronary thrombosis or myocardial necrosis?" Before attempting to answer this question, changes observed routinely in the coronary arteries in fatal ischemic heart disease (IHD) will be reviewed: 1) The coronary arteries are diffusely involved by atherosclerotic plaques.' Although the lumens of some segments are more severely narrowed than others, all portions of the extramural coronary tree are involved by the atherosclerotic process. 2) In fatal IHD, with rare exception, the lumens of at least two of the three major coronary arteries are >75% narrowed by old atherosclerotic plaques.' The most severe narrowing tends to be in the more proximal portions of the left anterior descending and left circumflex branches; the distal half of the right coronary artery is prone to narrowing that is as severe as that in its proximal portion. 3) The atherosclerotic process is limited to the epicardial coronary arteries, i.e., the mnajor trunks and their near right-angle branches. The intramural (intramyocardial) coronary arteries are spared by the atherosclerotic process. 4) The coronary artery responsible for perfusing with oxygen the area of myocardial ischemia is not necessarily the most severely narrowed of the 3 major coronary arteries but its lumen is virtually always >75% narrowed at some point by atherosclerotic plaques.