Acute coronary syndrome or ACS is an umbrella term used for any condition characterized by symptoms of acute myocardial ischemia caused by an abrupt reduction in blood flow to the heart. Three related but distinct clinical entities fall under the category of ACS; Unstable Angina (UA), Non ST segment elevation myocardial infarction (NSTEMI), and ST-segment elevation myocardial infarction (STEMI)
Unsable Angina; This occurs when a thrombus partially or intermittently blocks blood flow through a coronary artery. It is characterized by the development of chest pain that may or may not radiate. The chest pain may be associated with additional symptoms such as dyspnea, diaphoresis, nausea, lightheadedness, elevated heart rate, hypo or hypertension, and arrhythmias. Chest pain occurs with rest or exertion: the pain and associated symptoms are severe enough to limit the patients activity. A 12 lead ECG will show transient / temporary ST- segment depression or T-wave inversion. Cardiac biomarkers are not elevated. Chest pain that occurs with minimal exertion or requires an increasing dose of sublngual nitroglycerine to obtain relief is defined as UA. It also includes prolonged episodes of chest pain at rest, any chest pain that increases in severity, or any chest pain that is very severe upon first presentation.
NSTEMI; Also occurs when a thrombus partially or intermittently blocks blood flow through a coronary artery. On initial presentation, it may be difficult to differentiate between UA and NSTEMI. Like unstable angina, it is characterized by chest pain that may or may not radiate to the arm, neck, back or epigastric region. The chest pain may be accompanied by additional symptoms such as dyspnea, diaphoresis, nausea, lightheadedness, tachycardia, hypo or hypertension, arrhythmia and a drop in oxygen saturation. Pain may occur at rest or with activity. Compared with UA chest pain in NSTEMI lasts longer and is more severe. A 12 lead ECG may show signs indicative of myocardial ischemia.; ST segment depression or T wave inversion. Diagnosis of NSTEMI is made on the basis of elevated cardiac biomarkers.
STEMI; Occurs when a thrombus fully occludes a coronary artery resulting in necrosis of part of the myocardium. Development of an acute MI is characterized by a central necrotic area surrounded by zone of injury. Tissue in the zone of injury can recover if blood flow is restored quickly enough; if it is not, the area of injury will become necrotic. The zone of injury in turn, is surrounded by outer zone of reversible ischemia. Like other forms of ACS, STEMI is characterized by chest pain that may or may not radiate to the arm, neck, back, or epigastric region. Accompanying symptoms may include dyspnea, diaphoresis, nausea, lightheadedness, tachycardia, tachypnea, hypo or hypertension, a drop in oxygen saturation and arrhythmias. Also like UA and NSTEMI, this pain may occur at rest or with exertion and is severe enough to limit the person's activity. Quantitatively, pain is longer in duration and more severe than chest pain in UA. Definitive diagnosis of STEMI is made on the basis of 12 lead ECG changes indicative of MI. Serum biomarkers are elevated.
Adherence to evidence based guidelines for the management of ACS has been associated with better patient outcomes and decreased risk for subsequent cardiac events such as recurrent ischemia/ infarct.