Presence and evolution of coronary atherosclerosis in relation to clinical and electrocardiographic patterns of myocardial ischemia.

The pathophysiology of ischemic heart disease is multifaceted. Atherosclerosis, spasm, thrombosis, and embolism, alone and in combination, play a role in the pathogenesis of myocardial ischemia. The effect of coronary occlusive disease may vary from patient to patient, producing stable or unstable angina, or myocardial infarction. Myocardial ischemia occurs when there has been an acute imbalance between oxygen demand and supply. A number of variables alter the relationship between the presence of myocardial ischemia and the degree of coronary stenosis. These include the length, location, and geometry of the stenosis; the presence or absence of collateral vessels; and the coronary arterial tone. Coronary arteriography has shown the same general extent and distribution of coronary artery disease in patients with stable and unstable angina. Differences in the severity of coronary artery disease emerge when the various forms of unstable angina pectoris are considered separately. More severe coronary disease is present in patients who present with a crescendo pattern of angina and in those who display either ST-segment deviations or T-wave inversions during chest pain. The precise mechanism for the production of unstable angina in any individual patient is unknown but may be related to several factors, including the rapid progression of coronary artery disease just before or during the onset of unstable angina; or intermittent transient coronary artery occlusion resulting from spasm, platelet aggregation, or thrombosis.