Acute Coronary Syndrome

Acute coronary syndrome (ACS) is the umbrella term for clinical presentations caused by sudden reduction of blood flow to the myocardium, almost always from acute coronary thrombosis on a disrupted atherosclerotic plaque. It encompasses unstable angina and acute myocardial infarction (with and without ST-segment elevation) and represents the acute, unstable end of the coronary artery disease spectrum.

Definition

Acute coronary syndrome is a group of conditions — unstable angina, non-ST-elevation myocardial infarction, and ST-elevation myocardial infarction — produced by acute myocardial ischemia, typically resulting from thrombus formation on a ruptured or eroded coronary atherosclerotic plaque.

Scope

This topic covers the concept, pathophysiology, and classification of acute coronary syndrome as a clinical entity, including how it relates to plaque disruption and to the spectrum from unstable angina to ST-elevation myocardial infarction. It is a reference description and does not provide diagnostic thresholds or treatment instructions for individuals.

Core questions

• What unifies unstable angina and the two types of myocardial infarction under one syndrome?
• How does plaque disruption convert stable coronary disease into an acute event?
• How are ST-elevation and non-ST-elevation presentations distinguished conceptually?
• Where does acute coronary syndrome sit on the spectrum of coronary artery disease?

Key concepts

• Plaque rupture and erosion
• Coronary thrombosis
• Unstable angina
• Non-ST-elevation myocardial infarction (NSTEMI)
• ST-elevation myocardial infarction (STEMI)
• Cardiac troponin as a marker of myocardial injury
• Supply-demand ischemia

Mechanisms

Acute coronary syndrome usually begins when a vulnerable atherosclerotic plaque ruptures or erodes, exposing thrombogenic material and triggering platelet aggregation and thrombus formation in the coronary lumen (Hansson, 2005). A non-occlusive or transient thrombus typically produces unstable angina or non-ST-elevation myocardial infarction, whereas complete, persistent occlusion characteristically produces ST-elevation myocardial infarction; the distinction between unstable angina and infarction rests on whether myocardial injury, detected by rising cardiac troponin, has occurred (Thygesen, 2018; Byrne, 2023).

Clinical relevance

Acute coronary syndrome is a leading cause of acute hospitalization and cardiovascular death, and recognizing it as a continuum of plaque-driven ischemia frames why rapid restoration of coronary flow and risk stratification are central themes in cardiology (Byrne, 2023). This entry describes the syndrome for educational reference and is not a basis for individual diagnosis or treatment.

Epidemiology

Acute coronary syndromes account for a large share of emergency cardiac presentations and of ischemic-heart-disease mortality worldwide; incidence rises with age and cardiovascular risk-factor burden, with broader epidemiology covered in the parent area.

Evidence & guidelines

The 2023 European Society of Cardiology guidelines consolidate the contemporary definition, classification, and evidence-based management of acute coronary syndromes into a single framework, and the Fourth Universal Definition of Myocardial Infarction provides the standardized criteria for distinguishing infarction within the syndrome (Byrne, 2023; Thygesen, 2018).

History

The grouping of unstable angina and myocardial infarction under a single 'acute coronary syndrome' concept reflects the recognition that they share a common pathophysiology of plaque disruption and thrombosis. Successive universal definitions of myocardial infarction (Thygesen, 2018) and ESC guidelines (Byrne, 2023) have refined the classification, notably by unifying the management of the spectrum and centring it on cardiac troponin.

Debates

Defining myocardial injury thresholds with high-sensitivity troponin

More sensitive troponin assays detect smaller amounts of myocardial injury, sharpening early diagnosis but also raising questions about how to interpret minor elevations and distinguish type 1 (plaque-driven) from type 2 (supply-demand) myocardial infarction.

Key figures

• Robert A. Byrne
• Kristian Thygesen
• Göran K. Hansson

Seminal works

• thygesen-2018
• byrne-2023

Frequently asked questions

What is the difference between acute coronary syndrome and a heart attack?

Acute coronary syndrome is the broader category that includes unstable angina and both types of myocardial infarction. A 'heart attack' usually means myocardial infarction specifically, which is one part of the acute coronary syndrome spectrum where actual myocardial injury occurs.

What separates unstable angina from a myocardial infarction within ACS?

Both arise from acute myocardial ischemia, but myocardial infarction involves detectable myocardial injury, marked by a rise in cardiac troponin, whereas unstable angina is ischemia without that biomarker evidence of cell death.