Acute Coronary Syndrome (ACS)

How to Cite This Chapter: Hijazi W, Jolly SS, Budaj A, Bednarz B, Leśniak W. Acute Coronary Syndrome (ACS). McMaster Textbook of Internal Medicine. Kraków: Medycyna Praktyczna. https://empendium.com/mcmtextbook/chapter/B31.II.2.5.3..html Accessed December 05, 2025.
Last Reviewed: May 2, 2025
Last Updated: May 2, 2025
Chapter Information

Acute coronary syndrome (ACS) is a clinical syndrome of acute chest pain related to acute myocardial ischemia. ACS is classified based on electrocardiography (ECG) results into ST-segment elevation ACS and non–ST-segment elevation ACS. This approach has important practical implications because patients presenting with ST-segment elevation ACS require immediate reperfusion therapy.

ACS with troponin elevation (myocardial infarction [MI]) is differentiated from myocardial injury by the presence of clinical markers of ischemia. Patients with MI have troponin elevations in addition to at least one of ischemic signs or symptoms, new regional wall motion abnormalities, or evidence of angiographic changes or typical findings on ECG. In contrast, patients with myocardial injury have troponin elevations without these other features.

DefinitionTop

Classification of ACS: see Ischemic Heart Disease.

Definition of myocardial infarction: see Table 3.11-1.

1. Non–ST-segment elevation ACS could present as unstable angina (UA) or as non–ST-segment elevation myocardial infarction (NSTEMI), with the latter having elevated serum markers of myocardial necrosis. There is no acute ST-segment elevation seen on ECG. Clinical, ECG, and imaging features of myocardial ischemia may be similar. Patients with UA/NSTEMI constitute a heterogeneous group due to the complex pathogenesis, which includes atherosclerotic plaque rupture with superimposed thrombosis, progressive obstruction of a coronary artery, arterial constriction, inadequate oxygen supply relative to myocardial demand, or spontaneous coronary dissection.

2. ST-segment elevation myocardial infarction (STEMI) is a clinical syndrome usually caused by the cessation of blood flow through a coronary artery due to its occlusion, which results in transmural ischemia leading to ST-segment elevation and myocardial necrosis manifested by increased blood levels of specific biomarkers. The most common mechanism is atherosclerotic plaque rupture with superimposed thrombosis.

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