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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 National Registry of Myocardial Infarction (NRMI) database, from 1994 to 1999, the prevalence of STEMI decreased from 36.4% to 27.1% with concomitant rise of NSTEMI from 45% to 63%. Similar trends were also observed in a population study from 1999 to 2008. Despite this, the age-adjusted mortality for NSTEMI patients has been gradually declining, likely due to advancement in the treatment for acute coronary syndrome.
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Angina pectoris is the symptomatic equivalent of transient myocardial ischemia, which 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 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 has been estimated that about 43.6% of patients with USA/NSTEMI presented without chest pain. The clinical presentation of unstable angina can take any one of several forms.
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