Acute Coronary Syndrome
Acute coronary syndrome (ACS) is a spectrum of life-threatening conditions caused by a sudden reduction in blood flow to the heart muscle due to acute obstruction of a coronary artery[^c1]. It encompasses ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI), and unstable angina, which are distinguished by the presence and extent of myocardial necrosis and the characteristic electrocardiographic findings[^c2]. ACS represents the acute manifestation of coronary artery disease and is a leading cause of morbidity and mortality worldwide. Cardiovascular diseases caused an estimated 19.8 million deaths globally in 2022, with heart attacks and strokes accounting for 85% of these fatalities[^c4]. Each year, over 800,000 individuals in the United States experience a heart attack[^c7].
The most common underlying cause of ACS is acute thrombus formation over a ruptured or eroded atherosclerotic plaque in a coronary artery[^c3]. Inflammation plays a central role in plaque destabilization: activated immune cells weaken the fibrous cap of the plaque, predisposing it to rupture[^c5]. Once the thrombogenic core is exposed, platelets are activated and the coagulation cascade is triggered, leading to partial or complete coronary occlusion. In more than half of cases, the pre-event stenosis is less than 40%, highlighting that plaque biology, rather than the degree of luminal narrowing, determines the risk of acute events[^c6].
Diagnosis of ACS rests on clinical presentation, electrocardiography, and cardiac biomarkers. The electrocardiogram is the most important initial test and should be obtained within 10 minutes of first medical contact. High-sensitivity cardiac troponin assays enable early detection of myocardial necrosis. Management depends on the classification of ACS: STEMI requires emergency reperfusion with percutaneous coronary intervention or fibrinolysis, while NSTEMI and unstable angina are managed with intensive medical therapy followed by risk-stratified angiography. The 2025 ACC/AHA multisociety guideline updated standards for dual antiplatelet therapy, radial access preference, intravascular imaging (upgraded to Class 1A), and complete revascularization for both STEMI and NSTE-ACS.
Despite advances in care, ACS carries a significant burden of complications. In a nationwide study of 1.56 million survivors, cardiovascular mortality reached 9.37% at four years, with non-cardiovascular causes accounting for a growing proportion of deaths over time[^c8]. Cardiogenic shock occurs in approximately 10% of acute MI patients with 40 to 50% early mortality. Long-term secondary prevention through lifestyle modification, cardiac rehabilitation, and pharmacotherapy—including statins, antiplatelet agents, and neurohormonal antagonists—is essential for reducing recurrent events and improving survival.