Acute coronary syndromes include ST-elevation myocardial infarction (STEMI) and unstable coronary artery disease. The latter includes non-ST-elevation myocardial infarction (NSTEMI) and unstable angina.
Persistent ST-segment elevation generally reflects transmural ischemia by total coronary occlusion and characterizes evolving myocardial infarction (STEMI). This occurs in a relatively small population of patients with acute coronary syndrome. In these settings, the therapeutic objective is either primary angioplasty or fibrinolytic treatment to achieve rapid and complete recanalization.1
Patients with NSTEMI or unstable angina present with chest pain associated with ST-depression, T-wave inversion, flat T waves, or nonspecific ECG changes; a normal ECG at presentation can also be the case. NSTEMI is distinguished from unstable angina by an elevation in serum biochemical markers of myocardial necrosis (troponin T or I). However, the elevation of troponin levels may also be caused by either transient occlusion or microembolization secondary to spontaneous thrombolysis (small infarcts), and hence in the absence of an epicardial coronary artery occlusion amenable to percutaneous revascularization.
Patients with unstable acute coronary syndrome are at risk for myocardial infarction, MI recurrence, or death. Diagnosis and risk stratification are pursued together: During the process of establishing the acute coronary syndrome diagnosis, risk is repeatedly assessed and used as guidance for choosing the best therapeutic strategy. According to the European Guidelines,2 risk stratification of patients with unstable angina/NSTEMI involves integrating relevant information from their histories; e.g., chest pain pattern, physical examination, ECG, and biochemical cardiac markers.
Several clinical decision rules are available for risk stratification: the thrombosis in myocardial infarction (TIMI) score,3 the global registry of acute coronary events (GRACE) score, the fast revascularization in instability in coronary disease (FRISC) score,5 and the platelet glycoprotein IIb/IIIa in unstable angina receptor suppression using Integrilin (PURSUIT) score.6 According to these algorithms, patients can be assigned to low-, intermediate-, or high-risk categories. The presence of thrombus and extent of underlying coronary artery disease (CAD), in particular troponin elevation and signs and symptoms of ongoing myocardial ischemia, can modify a patient's risk category.
Optimal early management of patients with non-ST-elevation acute coronary syndrome is still being debated. Several large randomized trials7-9 and a meta-analysis10 compared a routine invasive strategy (i.e., early angiography possibly followed by revascularization) with a more conservative strategy (i.e., angiography and revascularization only if medical therapy failed or residual ischemia was documented).10 The early invasive strategy was found to be superior to the conservative strategy in reducing major cardiovascular events as well as severe angina and rehospitalization. In particular, RITA-3 (randomized intervention trial of unstable angina)9 was the first study reporting improved survival after early invasive intervention.
Another study11 of 1200 patients with non-ST-elevation acute coronary syndrome demonstrated that if patients were optimally treated before, during, and after revascularization, early cardiac catheterization was not better than a more selective invasive strategy in terms of mortality and recurrence of acute myocardial infarction. These investigators reported that the restricted use of conventional angiography only in patients experiencing refractory angina or clinically significant ischemia on predischarge exercise tests saved 47% of catheterization procedures without any detrimental effect on long-term follow-up.11 A large number of these procedures were merely diagnostic and not followed by revascularization. Results were confirmed at four-year follow-up,12 suggesting that only very high risk patients should undergo early invasive management. Medical therapy might be tailored to the patient's risk profile.3,6,13,14
