As discussed in detail in Chap. 56, acute coronary syndrome (ACS) is a term used to describe a pattern of clinical symptoms that is consistent with acute myocardial ischemia (Fig. 59–1).1 This chapter discusses two closely related forms of ACS, namely unstable angina (UA) and non–ST-segment elevation myocardial infarction (NSTEMI). NSTEMI (see Fig. 59–1) usually does not progress to Q-wave myocardial infarction (QWMI) but rather to non–Q-wave myocardial infarction (NQMI). Infrequently, NSTEMI evolves to become QWMI by electrocardiography (ECG).
Definitions and pathophysiology of acute coronary syndromes (ACS). Whereas the large majority of patients with ST-segment elevation (large arrows) have complete thrombotic occlusion of an epicardial coronary artery and ultimately develop a Q-wave myocardial infarction (QWMI), a minority (small arrow) develop a non–Q-wave myocardial infarction (NQMI). Patients who present without ST-segment elevation tend to have nonocclusive thrombus and experience either unstable angina or a non–ST-segment elevation myocardial infarction (NSTEMI). Adapted with permission from Davies MJ. Pathophysiology of acute coronary syndromes. Heart 2003;83:361.
The pathophysiology of UA and NSTEMI are very similar, typically involving rupture (or less commonly erosion) of an atherosclerotic plaque with thrombus formation that severely obstructs the coronary artery lumen. Accordingly, patients with either of these syndromes are frequently treated similarly with individual variations in management depending on the classification of patient risk.1 They differ primarily in whether the ischemia is severe enough to lead to a detectable release of a marker of myocardial injury (troponin I, troponin T, or creatine kinase myocardial band [CK-MB]).
This chapter discusses the current management of patients with UA/NSTEMI and discusses another rest angina syndrome mediated by different underlying pathophysiology, namely, variant angina.
UA/NSTEMI is also termed non–ST-elevation ACS (NSTE ACS). Angiographic, intravascular ultrasound (IVUS), and angioscopic studies indicate that UA/NSTEMI usually results from the disruption of an atherosclerotic plaque with a subsequent platelet-rich thrombus that obstructs coronary blood flow. The initial diagnosis and management are based on information available at the time of presentation and are updated using new information accumulated over time.1 The initial diagnosis may be challenging because NSTEMI often cannot be differentiated from UA at the time of initial presentation. Moreover, distinguishing UA from the multiple nonischemic causes of chest discomfort may prove difficult and resource intensive.
A patient with symptoms consistent with ACS should have an ECG performed and interpreted within 10 minutes. The most important goal of the early ECG is to identify patients with STEMI who are candidates for immediate reperfusion therapy. Each patient should be given a provisional diagnosis of (1) definite ACS, which should be classified as STEMI, NSTEMI, or UA; (2) possible ACS; (3) a non-ACS cardiac condition (eg, chronic stable angina or heart failure); or (4) a noncardiac diagnosis, which should be as specific as possible. ...