Acute coronary syndrome (ACS) is an emergent situation characterized by an acute onset of myocardial ischemia that results in myocardial death (i.e., myocardial infarction [MI]) if definitive interventions do not occur promptly. (Although the terms coronary occlusion, heart attack, and myocardial infarction are used synonymously, the preferred term is myocardial infarction.) The spectrum of ACS includes unstable angina, non-ST-segment elevation MI (NSTEMI), and ST-segment elevation MI (STEMI).

In unstable angina, blood flow in a coronary artery is reduced, often caused by the rupture of an atherosclerotic plaque. A clot begins to form, but the artery is not completely occluded. This is an acute situation that can result in chest pain and other symptoms and is sometimes referred to as preinfarction angina because the patient will likely have an MI if prompt interventions do not occur.

In an MI, plaque rupture and subsequent thrombus formation result in complete occlusion of the artery, leading to ischemia and necrosis of the myocardium supplied by that artery. Vasospasm (sudden constriction or narrowing) of a coronary artery, decreased oxygen supply (e.g., from acute blood loss, anemia, or low blood pressure), and increased demand for oxygen (e.g., from a rapid heart rate, thyrotoxicosis, or ingestion of cocaine) are other causes of MI. In each case, a profound imbalance exists between myocardial oxygen supply and demand. The area of infarction develops over minutes to hours; the expression “time is muscle” reflects the urgency of appropriate treatment to improve patient outcomes. An MI may be defined by the type, the location of the injury to the ventricular wall (anterior, inferior, posterior, or lateral wall), or by the point in time in the process of infarction (acute, evolving, old).

In many cases, the signs and symptoms of MI cannot be distinguished from those of unstable angina—hence, the evolution of the term acute coronary syndrome.

• Chest pain that occurs suddenly and continues despite rest and medication is the primary presenting symptom.
• Some patients have prodromal symptoms or a previous diagnosis of coronary artery disease (CAD), but others report no previous symptoms.
• Patient may present with a combination of symptoms, including chest pain, shortness of breath, indigestion, nausea, and anxiety.
• Patient may have cool, pale, and moist skin; heart rate and respiratory rate may be faster than normal. These signs and symptoms, which are caused by stimulation of the sympathetic nervous system, may be present for only a short time or may persist.

• Patient history (description of presenting symptom; history of previous illnesses and family health history, particularly of heart disease): History should also include information about patient's risk factors for heart disease.
• 12-lead electrocardiogram (ECG) within 10 minutes of pain onset or arrival at the emergency department: ECG findings are used to categorize the type of ACS (e.g., unstable angina, STEMI, or NSTEMI).
• Echocardiography to evaluate ventricular function, including wall motion and ejection fraction.
• Cardiac enzymes and biomarkers (creatine kinase isoenzymes, myoglobin, and troponin).

The goals of medical management are to minimize myocardial damage, preserve myocardial function, and prevent complications such as lethal dysrhythmias and cardiogenic shock.

• Initial management includes supplemental oxygen, aspirin, nitroglycerin, and morphine.
• Reperfuse via emergency use of thrombolytic medications or percutaneous coronary intervention (PCI).
• Reduce myocardial oxygen demand and increase oxygen supply with medications, oxygen administration, and bed rest.
• Perform coronary artery bypass or minimally invasive direct coronary artery bypass (MIDCAB).
• After the patient with an MI is free of symptoms, initiate a multiphase cardiac rehabilitation program.