Acute Coronary Syndrome I: Introduction

Acute Coronary Syndrome (ACS) refers to heart conditions caused by sudden obstruction of coronary arteries, typically from a ruptured atherosclerotic plaque leading to blood clot formation. This obstruction can partially or completely block blood flow, causing varying degrees of myocardial ischemia or infarction. ACS represents a medical emergency requiring prompt diagnosis and intervention.

Unstable angina shows transient ST-segment depression, elevation, or T-wave inversion with normal or mildly elevated high-sensitivity troponin, indicating ischemia without myocardial necrosis. NSTEMI displays ST-segment depression or T-wave inversion with significantly elevated troponin I or T and CK-MB, confirming subendocardial myocardial injury from partial coronary blockage.

STEMI is characterized by persistent ST-segment elevation in two or more contiguous leads, distinguishing it from unstable angina and NSTEMI, which show transient or no ST elevation. STEMI also presents with significantly elevated troponin I, T, and CK-MB, reflecting transmural myocardial infarction from complete coronary artery blockage.

Differentiating between these ACS types is critical for determining appropriate treatment strategies. Unstable angina and NSTEMI typically require antiplatelet therapy, anticoagulation, and possible coronary angiography, while STEMI demands immediate reperfusion therapy such as percutaneous coronary intervention or thrombolysis to restore blood flow and minimize cardiac damage.

NSTEMI involves partial or temporary coronary artery blockage causing ischemic injury confined to the subendocardium, the innermost heart muscle layer. STEMI results from complete and prolonged coronary artery obstruction causing irreversible myocardial necrosis across the entire thickness of the heart wall, known as transmural infarction.

Unstable angina typically shows normal or only mildly elevated high-sensitivity troponin levels due to minor ischemic injury without myocardial necrosis. In contrast, both NSTEMI and STEMI demonstrate significantly elevated troponin I or T and creatine kinase MB (CK-MB), indicating actual myocardial cell death and tissue damage.

Unstable angina results from variable or intermittent blockage causing ischemia without necrosis. NSTEMI involves partial blockage creating an oxygen supply-demand mismatch in subendocardial tissue. STEMI results from complete blockage causing transmural myocardial necrosis. The extent and duration of obstruction directly determine the severity of myocardial injury and clinical outcomes.