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ESSENTIALS OF DIAGNOSIS
New or worsening symptoms (angina, pulmonary edema) or signs (electrocardiographic [ECG] changes) of myocardial ischemia.
Absence or mild elevation of cardiac enzymes (troponin I or T) without prolonged ST-segment elevation on ECG.
Unstable angina and non-ST elevation myocardial infarction (MI) (USA/NSTEMI) are closely related in pathogenesis and clinical presentation and are therefore discussed as one entity in this chapter.
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GENERAL CONSIDERATIONS
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Unstable angina and non-ST elevation myocardial infarction (USA/NSTEMI) are a part of the wide spectrum of clinical manifestations of atherosclerotic coronary artery disease (Table 7–1). Compared with ST elevation myocardial infarction (STEMI), the incidence of USA/NSTEMI has been increasing. According to the Nationwide Inpatient Sample databases, from 2002 to 2011, the prevalence of NSTEMI increased from 52.8% to 68.6%. The risk-adjusted in-hospital mortality for NSTEMI patients has been gradually declining in the same period, likely due to advances in the treatment of acute coronary syndrome and increased utilization of early invasive strategy.
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Angina pectoris is the symptomatic equivalent of transient myocardial ischemia that results from a temporary imbalance in the myocardial oxygen demand and supply. Most episodes of myocardial ischemia are generally believed to result from an absolute reduction in regional myocardial blood flow below basal levels, with the subendocardium carrying a greater burden of flow deficit relative to the epicardium, whether triggered by a primary reduction in coronary blood flow or an increase in oxygen demand. USA/NSTEMI shares a more or less common pathophysiologic substrate with STEMI, which is usually due to ruptured/eroded or unstable atherosclerotic plaques with overlying thrombus formation, leading to reduced coronary blood flow. The differences in clinical presentation result largely from the differences in the magnitude of coronary occlusion, the duration of the occlusion, the modifying influence of local and systemic blood flow, and the adequacy of coronary collaterals.
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USA/NSTEMI is a clinical syndrome characterized by symptoms of ischemia, which may include classic retrosternal chest pain or such pain surrogates as a burning sensation, feeling of indigestion, or dyspnea (Table 7–2). Anginal symptoms may also be felt primarily or as radiation in the neck, jaw, teeth, arms, back, or epigastrium. The pain of unstable angina typically lasts 15–30 minutes; it can last longer in some patients. In some patients, particularly the elderly, dyspnea, fatigue, diaphoresis, light-headedness, a feeling of indigestion and the desire to burp or defecate, or nausea and emesis may accompany other symptoms or may be the only symptoms. It ...