Cardiac disease is usually manifested by symptoms of chest pain, dyspnea or respiratory distress, cardiac arrest, 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.
Myocardial ischemia (with attendant angina pectoris) results from an imbalance between myocardial oxygen supply and demand. Clinical findings vary depending on the severity of ischemia and on the frequency, duration, and rapidity of onset of ischemic episodes. If the demand for myocardial blood flow exceeds the capacity of the obstructed coronary arterial tree to supply it, the discomfort (angina pectoris) lasts until the excessive demand for coronary flow is reduced.
Discomfort is more intense and lasts longer when coronary blood flow decreases markedly, as occurs with sudden marked increase in coronary artery obstruction resulting from abrupt development of thrombus over an atherosclerotic plaque, embolization to a coronary artery, or sudden occlusion by coronary artery spasm. If myocardial necrosis then occurs, the condition is termed myocardial infarction; otherwise, the episode is one of acute coronary insufficiency, or preinfarction angina.
If obstruction is so severe that coronary blood flow is barely adequate to meet resting demands, even small increases in myocardial oxygen demand may cause angina. In addition, small aggregations of platelets on a ruptured plaque, spasm, or increased vasomotor tone can cause minor changes in the caliber of the severely obstructed coronary artery and precipitate angina.
Myocardial ischemia can exist in the absence of any chest discomfort. In patients with severe ischemia, 24-hour electrocardiographic (ECG) monitoring shows that 80% of the episodes of ST-segment depression lasting for a minute or more are present without angina (so-called silent ischemia). Painless myocardial infarction is not unusual in elderly or diabetic patients.
A. Stable Angina (Angina of Effort)
By definition, the pattern of discomfort, frequency of occurrence, and precipitating factors have remained the same for 3 or more months. Discomfort is usually substernal but may originate in other areas (eg, elbow, forearm, shoulder, neck interscapular region, or jaw), although substernal discomfort eventually occurs. It is usually precipitated by activities that increase myocardial oxygen consumption (eg, exercise, eating, or emotional upset), lasts longer than 1 minute and usually less than 15 minutes, and is usually relieved by rest or nitroglycerin (NTG). Pain that meets these criteria usually indicates the presence of fixed coronary obstruction. The most important feature suggesting the diagnosis ...