Acute coronary syndrome (ACS)
Also known as: ACS
Acute coronary syndrome (ACS) is a spectrum of conditions caused by a sudden reduction in blood flow to the heart muscle, encompassing unstable angina, NSTEMI, and STEMI. It most often results from rupture of an atherosclerotic plaque with thrombus formation.
Acute coronary syndrome (ACS) is the umbrella term for conditions caused by an abrupt drop in coronary blood flow to the myocardium. The usual trigger is rupture or erosion of an atherosclerotic plaque in a coronary artery, exposing its core and provoking platelet aggregation and thrombus formation that partially or completely occludes the vessel.
ACS spans three entities distinguished by ECG findings and cardiac biomarkers. Unstable angina is ischemic chest pain at rest or with minimal exertion, without myocardial necrosis — troponin remains negative. NSTEMI (non-ST-elevation myocardial infarction) shows elevated troponin without ST-segment elevation, typically reflecting a partially occluding thrombus and subendocardial infarction. STEMI (ST-elevation myocardial infarction) shows ST elevation with positive troponin, indicating complete occlusion and transmural infarction.
The classic presentation is crushing substernal chest pressure radiating to the left arm or jaw, with diaphoresis, dyspnea, and nausea — though women, older adults, and patients with diabetes may present atypically. Evaluation centers on the ECG and serial troponin measurements, and the distinctions matter clinically because STEMI demands immediate reperfusion.
The USMLE Step 1 tests ACS pathophysiology in depth: plaque rupture, the timeline of infarct evolution, ECG and biomarker patterns, and complications such as arrhythmias and ventricular rupture. The NPTE and NPTE-PTA cover ACS in cardiovascular foundations, emphasizing recognition of anginal symptoms and precautions during rehabilitation of cardiac patients.
Key takeaways
- ACS includes unstable angina, NSTEMI, and STEMI, all caused by acute reduction of coronary blood flow.
- The usual mechanism is atherosclerotic plaque rupture with thrombus formation.
- Unstable angina has negative troponin; NSTEMI has positive troponin without ST elevation; STEMI has both ST elevation and positive troponin.
- USMLE Step 1 tests ACS diagnosis and infarct pathology; the NPTE exams emphasize symptom recognition and rehab precautions.