Pathophysiology and Definition of the Acute Coronary Syndromes

The acute coronary syndromes include ST elevation myocardial infarction, non-ST elevation myocardial infarction, and unstable angina. The latter two conditions are distinguished by evidence of myocardial infarction based on the elevation of cardiac injury markers. The underlying pathophysiology in the great majority of patients with ACS is atherothrombosis, which encompasses chronic coronary atherosclerotic disease and superimposed acute thrombotic occlusion. Rupture of a coronary atherosclerotic plaque initiates platelet activation and thrombotic coronary occlusion as well as a cascade of clotting mechanisms and inflammatory agents that contribute to myocardial ischemia and necrosis. Patients typically present with chest discomfort but a variety of ischemic equivalents may also predominate (dyspnea, lightheadedness, and cardiac failure). Typically, total coronary occlusion is associated with ST-segment elevation and elevation of injury markers of necrosis. With partial occlusion, there are usually ST and/or T wave abnormalities. All ACS patients are treated with intensive antithrombotic and anticoagulation therapy, as well management of associated problems such as ischemia heart failure and arrhythmias. Optimal treatment of ST elevation infarction is urgent coronary reperfusion, preferably by percutaneous coronary intervention (PCI). Non-ST elevation ACS patients receive comprehensive medical therapy and the majority undergo invasive evaluation within 48 hours of admission to determine their suitability for revascularization by PCI (˜90% of patients) or coronary bypass surgery (˜10% of patients). Of importance is the finding that, although mortality and morbidity of ST elevation infarction are higher than with non-ST elevation ACS during the acute phase, long-term prognosis is worse with non-ST elevation ACS. Therefore, intensive, acute, and long-term management of all patients with ACS is crucial and includes antithrombotic therapy, management of coronary risk factors, and treatment of associated cardiac conditions.