Acute Coronary Syndrome

Acute coronary syndrome (ACS) is an umbrella term for the clinical conditions caused by acute myocardial ischaemia, spanning unstable angina, non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI). The shared substrate is sudden reduction in coronary blood flow, usually from disruption of an atherosclerotic plaque, and the syndrome is classified using the electrocardiogram and cardiac troponin.

Definition

Acute coronary syndrome denotes a group of conditions resulting from acute myocardial ischaemia, conventionally divided by the presenting electrocardiogram and biomarker findings into ST-elevation myocardial infarction, non-ST-elevation myocardial infarction, and unstable angina.

Scope

This topic defines the ACS spectrum, the pathophysiology linking its subtypes, and the diagnostic criteria and risk-stratification frameworks used in the emergency setting. It situates ACS within emergency medicine as a diagnostic and prognostic problem and treats management at the level of concepts and evidence rather than specific drug regimens.

Core questions

• What pathophysiology unifies the acute coronary syndrome spectrum?
• How are STEMI, NSTEMI, and unstable angina distinguished at presentation?
• Which criteria define myocardial infarction within acute coronary syndrome?
• How is short-term risk estimated in patients with acute coronary syndrome?

Key concepts

• Atherosclerotic plaque rupture and erosion
• Coronary thrombosis and supply-demand mismatch
• ST-elevation versus non-ST-elevation presentations
• Unstable angina, NSTEMI, and STEMI
• Universal definition of myocardial infarction
• GRACE and TIMI risk scores

Mechanisms

Acute coronary syndromes most often begin with rupture or erosion of a lipid-rich atherosclerotic plaque, exposing thrombogenic material and triggering platelet aggregation and thrombus formation. A persistently occluding thrombus that interrupts transmural perfusion typically produces ST-segment elevation and ongoing necrosis (STEMI), while a non-occluding or transiently occluding thrombus produces non-ST-elevation syndromes; when myocyte necrosis occurs and troponin rises, the diagnosis is NSTEMI, and when ischaemia occurs without detectable necrosis, the presentation is termed unstable angina (Thygesen et al., 2018; Byrne et al., 2023).

Clinical relevance

Recognising acute coronary syndrome and classifying its subtype guides the urgency of evaluation and the broad direction of care, since STEMI implies a need for prompt reperfusion while non-ST-elevation syndromes are stratified by risk. The diagnostic and prognostic frameworks summarised here describe how the evidence base is applied; they are educational and do not constitute individualised treatment recommendations.

Epidemiology

Acute coronary syndrome is a major cause of hospitalisation and mortality from ischaemic heart disease worldwide. Within the spectrum, non-ST-elevation presentations have become proportionally more common with the adoption of sensitive troponin assays, reflecting greater detection of myocardial injury (Roffi et al., 2015).

Evidence & guidelines

The 2023 ESC acute coronary syndromes guideline (Byrne et al., 2023) consolidated previously separate STEMI and NSTE-ACS recommendations into a single framework, building on the 2015 ESC NSTE-ACS guideline (Roffi et al., 2015). The Fourth Universal Definition of Myocardial Infarction (Thygesen et al., 2018) provides the diagnostic criteria, and validated tools such as the GRACE (Fox et al., 2006) and TIMI (Antman et al., 2000) scores support risk stratification.

History

The concept of acute coronary syndrome emerged as it became clear that unstable angina, NSTEMI, and STEMI share the common mechanism of plaque disruption and thrombosis. The shift from creatine kinase to troponin-based diagnosis, codified in successive universal definitions of myocardial infarction (Thygesen et al., 2018), refined how the subtypes are distinguished, and risk scores derived from large registries (Fox et al., 2006; Antman et al., 2000) brought structured prognostication into routine practice.

Seminal works

• thygesen-2018
• byrne-2023
• fox-2006
• antman-2000

Frequently asked questions

What are the three categories of acute coronary syndrome?

Acute coronary syndrome is conventionally divided into unstable angina, non-ST-elevation myocardial infarction (NSTEMI), and ST-elevation myocardial infarction (STEMI), distinguished by the electrocardiogram and cardiac troponin.

How is unstable angina distinguished from NSTEMI?

Both lack persistent ST-segment elevation, but NSTEMI involves detectable myocyte necrosis with a rise in cardiac troponin, whereas unstable angina is ischaemia without a troponin rise meeting the infarction threshold.