Cardiac disease is usually manifested by symptoms of chest pain, dyspnea or respiratory distress, cardiac arrest or syncope, or shock. Because these symptoms are so commonly encountered in the emergency department and they may result from disease in many organs other than the heart, they are discussed separately (Chapters 9, 10, 11, 13, and 14). Because almost any cardiac disease is at least potentially life-threatening, no attempt has been made in this chapter to categorize disorders on the basis of severity or to assign priorities in treatment.
Acute coronary syndrome (ACS) refers to a spectrum of conditions that develop from blood flow that is insufficient to meet the metabolic needs of the myocardium. Patients with an acute coronary syndrome exist on a clinical continuum from unstable angina to non-ST-segment elevation myocardial infarction to ST segment elevation myocardial infarction.
Acute Myocardial Infarction (Coronary Occlusion)
Myocardial infarction results when arterial blood flow to the myocardium is suddenly decreased or interrupted. It is usually due to atherosclerotic coronary artery disease with plaque rupture and sudden occlusion by thrombus; vasculitis or emboli are less common causes. Complete occlusion, most often with thrombus, is found in 80–90% of patients with chest pain and ST segment elevation who are studied by coronary angioplasty within several hours of onset. Occasionally, patients dying of myocardial infarction are found to have nonoccluded coronary arteries, and infarction in such cases is presumably due to spasm of a coronary artery or thrombosis with complete lysis. Cocaine use has been associated with acute myocardial infarction, probably as a result of coronary spasm with or without intravascular thrombus formation. In myocardial infarction, severely ischemic and infarcted muscle contracts and relaxes poorly or not at all; if infarction is extensive, decreased cardiac output with heart failure or shock may result. After myocardial infarction, the ventricle may become aneurysmal or may even rupture. If conducting tissue is ischemic or infarcted, conduction abnormalities may occur. The infarcted endocardium attracts platelets and fibrin that may form mural clots, which can subsequently embolize. During acute myocardial infarction, the myocardium can become electrically unstable, resulting in arrhythmias that are frequently life-threatening.
Upon occlusion of a coronary artery, necrosis occurs in a time-dependent course, proceeding from endocardium to epicardium, generally over 4–6 hours. When residual perfusion by collateral vessels is present or lysis or thrombus occurs—either spontaneously or as a result of therapy—there will be salvage of myocardium. The earlier the reperfusion, the more myocardium is salvaged.
Most patients with myocardial infarction have chest discomfort that is typically substernal and may radiate to the neck or left arm. However, pain can occur in atypical areas such as the right arm, shoulders, back, or epigastrium. The pain is classically oppressive or squeezing in character and may be ...