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Acute myocardial infarction (AMI) is a most common diagnosis in hospitalized patients in industrialized countries. In the United States, ~660,000 patients experience a new AMI, and 305,000 experience a recurrent AMI each year. About half of AMI-related deaths occur before the stricken individual reaches the hospital. Of note, the in-hospital mortality rate after admission for AMI has declined from 10 to about 5% over the past decade. The 1-year mortality rate after AMI is about 15%. Mortality is approximately fourfold higher in elderly patients (aged >75) as compared with younger patients.
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When patients with prolonged ischemic discomfort at rest are first seen, the working clinical diagnosis is that they are suffering from an acute coronary syndrome (Fig. 269-1). The 12-lead electrocardiogram (ECG) is a pivotal diagnostic and triage tool because it is at the center of the decision pathway for management; it permits distinction of those patients presenting with ST-segment elevation from those presenting without ST-segment elevation. Serum cardiac biomarkers are obtained to distinguish unstable angina (UA) from non-ST-segment elevation myocardial infarction (NSTEMI) and to assess the magnitude of an ST-segment elevation myocardial infarction (STEMI). Epidemiologic studies indicate there is a shift in the pattern of AMI over the last 15 years with more patients with NSTEMI than STEMI. This chapter focuses on the evaluation and management of patients with STEMI, while Chap. 268 discusses UA/NSTEMI.
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PATHOPHYSIOLOGY: ROLE OF ACUTE PLAQUE RUPTURE
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STEMI usually occurs when coronary blood flow decreases abruptly after a thrombotic occlusion of a coronary artery previously ...