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acute coronary syndrome overview definition classification 2025
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Here is a clear overview of Acute Coronary Syndrome (ACS):
What is ACS?
Acute Coronary Syndrome is an umbrella term for conditions caused by acute obstruction of blood flow through a coronary artery, resulting in myocardial ischemia or infarction. It represents a spectrum - from angina without heart muscle death, all the way to a full heart attack.
The Three Types of ACS
| Type | Key Features |
|---|---|
| Unstable Angina (UA) | Chest pain at rest, new onset, or worsening pattern - no elevation of troponin (no myocyte necrosis) |
| NSTEMI (Non-ST Elevation MI) | Chest pain + elevated troponin (myonecrosis confirmed) + no ST elevation on ECG |
| STEMI (ST Elevation MI) | Chest pain + elevated troponin + persistent ST elevation (>20 min) on ECG |
UA and NSTEMI together are called Non-ST Elevation ACS (NSTE-ACS), because they share the absence of ST elevation.
Pathophysiology (What Goes Wrong)
The trigger in most cases is rupture or erosion of an atherosclerotic plaque in a coronary artery. This leads to:
- Platelet aggregation at the rupture site
- Thrombus (clot) formation
- Partial or complete obstruction of coronary blood flow
- Ischemia or infarction of the downstream myocardium
This is called Type 1 MI - the most common mechanism.
Type 2 MI occurs without plaque rupture - instead there is a supply/demand mismatch (e.g., severe anemia, tachycardia, hypotension, or vasospasm like Prinzmetal angina).
Epidemiology
- ~1.2 million hospitalizations per year in the US
- About 2/3 are NSTE-ACS (NSTEMI or unstable angina)
- More than half of patients are over age 65
- Strong association with atherosclerosis risk factors (hypertension, diabetes, dyslipidemia, smoking)
Key Biomarkers
- Troponin I or T - the gold standard for detecting myocyte necrosis; elevated in both NSTEMI and STEMI
- CK-MB - also elevated in MI, though less specific than troponin
The 2025 ACC/AHA ACS Guideline (the most current) consolidates management recommendations for all ACS types, incorporating updated evidence on antiplatelet therapy, reperfusion strategy, and bleeding risk reduction.
Would you like to go deeper on any specific aspect - diagnosis, ECG findings, management, or medications?
- Goldman-Cecil Medicine, Chapter 57
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