Unstable Angina and Other Acute Coronary Syndromes

Patients with coronary artery disease (CAD) present clinically when their disease enters an unstable phase known as an acute coronary syndrome (ACS), in which the cap of a previously stable atheromatous coronary plaque ruptures or erodes, which in turn activates a thrombotic cascade that may lead to coronary artery occlusion, myocardial infarction (MI), cardiogenic shock, and patient death. There are nearly 2 million episodes of ACS in the United States annually; it is the most common reason for hospitalization with CAD and is the leading cause of death in the developed world. ACS patients include those with unstable angina (UA), non–ST segment elevation myocardial infarction (non-STEMI), and ST segment elevation myocardial infarction (STEMI) and patients who die suddenly of an arrhythmia precipitated by coronary occlusion. The distinction among various ACS subgroups reflects varying characteristics of clinical presentation (presence or absence of elevated cardiac biomarkers) and the type of electrocardiographic (ECG) changes manifested on the initial ECG at the time of hospitalization. This chapter focuses on UA and non-STEMI. A graph outlines mortality risks faced by patients wit