ACUTE CORONARY SYNDROME

✓ Medically ReviewedDISEASEID: MDBT0154🚨 TRIAGE: EMERGENCYICD-10: I24.9

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Definition

CLINICAL DEFINITION

Acute Coronary Syndrome (ACS) is a clinical umbrella term encompassing a spectrum of conditions resulting from a sudden reduction or blockage of blood flow to the heart muscle. It comprises ST-segment elevation myocardial infarction (STEMI), non-ST-segment elevation myocardial infarction (NSTEMI), and unstable angina (UA), differentiated by electrocardiographic changes and the presence or absence of myocardial necrosis biomarkers.

IN PLAIN ENGLISH

A sudden, severe reduction in blood flow to the heart muscle that can cause a heart attack or severe chest pain. It requires immediate medical attention to prevent permanent heart damage.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Acute Coronary Syndrome is NOT synonymous solely with a completed myocardial infarction (heart attack); it also includes unstable angina where myocardial necrosis has not yet occurred. It is also NOT chronic stable angina, which is predictable chest pain on exertion that resolves with rest.

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Word Breakdown

acute

=sharp, sudden, or severe (Latin 'acutus')

coron

=crown (Latin 'corona'), referring to the arteries encircling the heart

syndrome

=concurrence of symptoms (Greek 'syndrome')

Literal Meaning: A sudden concurrence of symptoms related to the crown-like heart arteries

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Abbreviations

ACS=Acute Coronary Syndrome — umbrella term for STEMI, NSTEMI, and unstable angina

STEMI=ST-Elevation Myocardial Infarction — complete epicardial coronary occlusion

NSTEMI=Non-ST-Elevation Myocardial Infarction — myocardial necrosis without persistent ST elevation

UA=Unstable Angina — myocardial ischaemia at rest or accelerating, without necrosis biomarkers

PCI=Percutaneous Coronary Intervention — primary reperfusion strategy for STEMI

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Synonyms & Variants

Acute Ischaemic Heart Syndrome›Acute Myocardial Infarction Spectrum›

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Category-Specific Context

As a Disease category, ACS represents a dynamic pathophysiological spectrum of acute myocardial ischaemia rather than a single static diagnosis. It is classified clinically and electrocardiographically into STEMI, NSTEMI, and unstable angina, which dictate divergent immediate management pathways regarding reperfusion therapies.

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Clinical Context & Usage

CLINICAL SETTINGS

Emergency DepartmentCardiac Care UnitCatheterisation LaboratoryIntensive Care UnitGeneral Medicine Ward

USAGE & DOCUMENTATION NOTES

In clinical documentation, ACS is frequently used as an initial working diagnosis before troponin results and ECG evolution clarify the specific subtype (STEMI, NSTEMI, or UA). Clinicians often document 'Rule out ACS' or 'ACS protocol initiated' in the emergency setting. Risk stratification tools like the GRACE or TIMI scores are routinely recorded in the assessment section to guide the urgency of invasive versus conservative management.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

ACS typically arises from the rupture or erosion of an atherosclerotic plaque in a coronary artery, exposing thrombogenic material to the bloodstream. This triggers platelet activation, aggregation, and the coagulation cascade, leading to the formation of an intracoronary thrombus. In STEMI, the thrombus causes complete and persistent occlusion of the epicardial coronary artery, resulting in transmural ischaemia and rapid myocardial necrosis. In NSTEMI, the occlusion is partial or intermittent, or collateral circulation is present, leading to subendocardial ischaemia and necrosis that is detectable by cardiac biomarkers but lacks persistent ST-segment elevation. In unstable angina, the thrombus reduces blood flow sufficiently to cause ischaemic symptoms at rest or with minimal exertion, but the ischaemia is not severe or prolonged enough to cause detectable myocyte necrosis and biomarker release.

PRIMARY CAUSES

Atherosclerotic plaque rupture

Exposure of the necrotic lipid core and tissue factor to the bloodstream triggers acute thrombosis and vessel occlusion.

Atherosclerotic plaque erosion

Loss of endothelial integrity without cap rupture exposes subendothelial matrix, promoting platelet adhesion and non-occlusive or occlusive thrombosis.

Coronary artery spasm (Prinzmetal's angina)

Severe focal or diffuse smooth muscle contraction causes transient, profound reduction in coronary blood flow, occasionally leading to thrombosis or infarction.

Spontaneous Coronary Artery Dissection (SCAD)

An intimal tear or intramural haematoma creates a false lumen that compresses the true lumen, obstructing coronary blood flow, predominantly in younger women.

Coronary embolism

Thrombi from the left atrium (e.g., atrial fibrillation) or paradoxical emboli lodge in the coronary circulation, causing abrupt occlusion.

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Drug-Induced Causes

💊 Cocaine and amphetamines ↗

Mechanism: Potent sympathetic stimulation causes severe coronary vasospasm, increased myocardial oxygen demand, and enhanced platelet aggregation, precipitating thrombosis.

→ Discontinue use; administer benzodiazepines, nitrates, and calcium channel blockers. Avoid non-selective beta-blockers due to unopposed alpha-adrenergic vasoconstriction.

💊 Capecitabine and 5-Fluorouracil (chemotherapy) ↗

Mechanism: Direct endothelial toxicity and smooth muscle contraction can induce severe coronary vasospasm leading to ischaemia or infarction.

→ Immediately withhold the offending chemotherapeutic agent; administer nitrates and calcium channel blockers. Cardiology consultation is required.

💊 Triptans (e.g., sumatriptan) ↗

Mechanism: Serotonin 1B/1D receptor agonism can cause coronary artery vasoconstriction, which may precipitate ischaemia in susceptible individuals.

→ Discontinue triptan. Contraindicated in patients with established ischaemic heart disease or ACS history.

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Epidemiology

Prevalence:ACS is a leading cause of morbidity and mortality globally. In high-income countries, the incidence is approximately 1 to 2 per 1,000 person-years, with NSTEMI now accounting for over 70% of all ACS presentations due to the increased sensitivity of contemporary troponin assays and an ageing population.

Age Group:Predominantly affects older adults (men >45 years, women >55 years), with incidence rising sharply with age. However, premature ACS can occur in younger adults with familial hypercholesterolaemia, substance abuse (e.g., cocaine), or conditions like SCAD.

Sex Predilection:Male

Geographic Distribution:Highest age-standardised incidence and mortality rates are observed in Eastern Europe, Central Asia, and parts of the Middle East, largely driven by high rates of smoking, hypertension, and dyslipidaemia. Incidence has been declining in many high-income Western countries due to improved primary prevention and acute management, though absolute numbers remain high due to ageing populations.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 EMERGENCY

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Atypical presentations in women, the elderly, and diabetic patients — these groups may present without classic chest pain, exhibiting only dyspnoea, fatigue, or nausea, leading to delayed diagnosis and increased mortality; maintain a low threshold for ECG and troponin testing.
Right ventricular infarction in inferior STEMI — characterised by hypotension, clear lungs, and elevated jugular venous pressure; requires avoidance of nitrates and diuretics, and aggressive fluid resuscitation to maintain preload.

URGENT EVALUATION TRIGGERS

New or presumed new ST-segment elevation ≥1 mm in two contiguous leads (or ≥2 mm in V1-V3 in men, ≥1.5 mm in women) — triggers immediate activation of the primary PCI pathway.
Dynamic ST-T wave changes or new left bundle branch block (LBBB) with ongoing ischaemic symptoms — requires urgent cardiology review and continuous monitoring.
Haemodynamic instability (hypotension, cardiogenic shock) or life-threatening arrhythmias (ventricular tachycardia/fibrillation) accompanying chest pain — mandates immediate resuscitation and emergency intervention.

Contraindications & Precautions

CONTRAINDICATIONS

Fibrinolytic therapy is absolutely contraindicated in NSTEMI and unstable angina
as it increases bleeding risk without improving outcomes and may promote further thrombosis.
Fibrinolytic therapy is contraindicated in STEMI if there is a history of haemorrhagic stroke
active internal bleeding
suspected aortic dissection
or recent major surgery/trauma.
Non-selective beta-blockers are contraindicated in the acute phase if the patient exhibits signs of acute heart failure
low cardiac output state
or high-degree atrioventricular block.

SPECIAL PRECAUTIONS

Avoid intramuscular injections in patients receiving anticoagulants or antiplatelets to prevent large haematomas.
Use caution with nitrates in patients with right ventricular infarction (often associated with inferior STEMI) or those who have recently used phosphodiesterase-5 inhibitors (e.g.
sildenafil)
due to the risk of profound hypotension.
Monitor renal function closely when prescribing low-molecular-weight heparins or specific P2Y12 inhibitors
adjusting doses as necessary.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Cardiogenic shock — severe pump failure leading to systemic hypoperfusion
most commonly associated with large anterior STEMI.
Ventricular arrhythmias (e.g.
ventricular fibrillation) — caused by acute ischaemia altering myocardial electrophysiology
a leading cause of pre-hospital sudden cardiac death.
Mechanical complications (e.g.
papillary muscle rupture
ventricular septal defect
free wall rupture) — typically occur 3–14 days post-MI due to necrotic tissue tearing.
Acute heart failure and pulmonary oedema — resulting from ischaemic diastolic or systolic dysfunction.
Pericarditis (epistenocardiac or Dressler's syndrome) — inflammation of the pericardium overlying the infarcted myocardium or as an autoimmune response weeks later.

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Acute Aortic Syndrome

Shares the 'acute' and 'syndrome' nomenclature and presents with severe chest pain; however, it involves the aorta (dissection, intramural haematoma) and requires entirely different, often opposing, management (e.g., avoiding anticoagulation).

Stable Angina

Both involve myocardial ischaemia, but stable angina is predictable, exertion-related, and relieved by rest, lacking the acute plaque rupture and thrombosis characteristic of ACS.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Acute Aortic Dissection

Key Distinguishing Feature: Tearing chest pain radiating to the back, pulse deficits, widened mediastinum on chest X-ray, and confirmed by CT aortography or transoesophageal echocardiography.

Pulmonary Embolism

Key Distinguishing Feature: Pleuritic chest pain, dyspnoea, tachycardia, right heart strain on ECG (S1Q3T3), and confirmed by CT pulmonary angiography or elevated D-dimer with high clinical probability.

Acute Pericarditis

Key Distinguishing Feature: Pleuritic chest pain relieved by sitting forward, diffuse concave ST-segment elevation with PR depression on ECG, and a pericardial friction rub.

Gastro-oesophageal Reflux Disease (GORD) / Oesophageal Spasm

Key Distinguishing Feature: Burning retrosternal pain related to meals or posture, normal ECG and troponin, and symptom relief with antacids or proton pump inhibitors.

Pneumothorax

Key Distinguishing Feature: Sudden unilateral pleuritic chest pain with dyspnoea, decreased breath sounds, and hyperresonance on the affected side, confirmed by chest X-ray.

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Clinical Pearls

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A normal initial high-sensitivity troponin and non-diagnostic ECG do not definitively rule out ACS if the symptom onset was very recent (e.g., <1–2 hours). Serial troponin testing at 0 and 1 (or 2) hours using validated accelerated algorithms is required for safe discharge.

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The presence of a new left bundle branch block (LBBB) or right bundle branch block (RBBB) can obscure ST-segment analysis. Use the Sgarbossa criteria (or modified Smith criteria) to identify concurrent STEMI in the presence of LBBB or ventricular paced rhythms.

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In patients with suspected ACS who have a history of recent cocaine use, benzodiazepines are the first-line therapy to reduce sympathetic drive, heart rate, and blood pressure. Non-selective beta-blockers should be avoided acutely due to the theoretical risk of unopposed alpha-adrenergic coronary vasoconstriction.

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Pre-treatment with P2Y12 inhibitors (like ticagrelor or prasugrel) before coronary anatomy is known in NSTEMI patients is no longer universally recommended by recent guidelines (e.g., ESC 2020) due to increased bleeding risk without clear ischaemic benefit; the decision should often be deferred until after angiography, unless a significant delay to angiography is anticipated.

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Example Usage & SOAP

CLINICAL SENTENCE

"The 62-year-old male presented to the Emergency Department with crushing central chest pain radiating to the left arm, and a 12-lead ECG revealed ST-elevation in leads II, III, and aVF, prompting immediate activation of the primary PCI pathway for acute STEMI."

IN A SOAP NOTE

S: 58-year-old female with a history of hypertension and type 2 diabetes presents with 45 minutes of severe, pressure-like substernal chest pain associated with diaphoresis and nausea. O: BP 145/85 mmHg, HR 92 bpm, RR 18, SpO2 98% on room air. Diaphoretic and anxious. Chest clear to auscultation. ECG shows 1.5 mm ST-depression in V3-V6 with T-wave inversions. High-sensitivity troponin I is elevated at 145 ng/L (upper reference limit 16 ng/L). A: Non-ST-Elevation Myocardial Infarction (NSTEMI). GRACE score indicates high risk. P: Administered aspirin 300 mg, ticagrelor 180 mg, and fondaparinux. Started intravenous glyceryl trinitrate for ongoing pain. Urgent cardiology referral for inpatient coronary angiography within 24 hours.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for acute chest pain with suspected ACS: (1) Acute Aortic Dissection — consider if pain is tearing and radiates to the back, check for pulse deficits and widened mediastinum; (2) Pulmonary Embolism — consider if pleuritic pain, tachycardia, and hypoxia are prominent, assess Wells score and D-dimer/CTPA; (3) Acute Pericarditis — consider if pain is pleuritic, positional, and ECG shows diffuse PR depression and concave ST elevation; (4) Gastrointestinal causes (e.g., oesophageal spasm, perforated ulcer) — consider if pain relates to meals or is associated with peritonitis.

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Classifications & Scoring

GRADING SYSTEM

Killip Classification

Grades the severity of heart failure in patients with acute myocardial infarction based on clinical examination. Class I: no heart failure; Class II: rales, S3, elevated JVP; Class III: acute pulmonary oedema; Class IV: cardiogenic shock.

SCORING TOOL

GRACE Score

Predicts in-hospital and 6-month mortality in patients with ACS using age, heart rate, systolic BP, creatinine, Killip class, cardiac arrest, ST deviation, and elevated cardiac enzymes. Guides the urgency of invasive management.

SCORING TOOL

TIMI Risk Score (UA/NSTEMI)

Estimates the 14-day risk of death, new/recurrent MI, or severe recurrent ischaemia requiring urgent revascularisation using 7 variables including age, risk factors, known CAD, aspirin use, recent severe angina, ST changes, and positive markers.

SCORING TOOL

HEART Score

Used in the emergency department to stratify the risk of major adverse cardiac events (MACE) within 6 weeks for patients with undifferentiated chest pain, based on History, ECG, Age, Risk factors, and Troponin.

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Prognosis

SHORT-TERM OUTCOME

In-hospital mortality for STEMI is approximately 5–10% with modern primary PCI, heavily dependent on time-to-reperfusion and the presence of cardiogenic shock. NSTEMI carries a lower immediate in-hospital mortality (2–5%) but a high rate of recurrent ischaemic events.

LONG-TERM PROGNOSIS

Long-term prognosis depends on left ventricular ejection fraction (LVEF), the extent of myocardial scar, and adherence to secondary prevention. Post-MI patients face a significantly elevated risk of recurrent cardiovascular events, heart failure, and sudden cardiac death over the subsequent 1–5 years.

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References & Coding

ICD-10 DIAGNOSTIC CODE

I24.9

LITERATURE CITATIONS & GUIDELINES

[1]Collet JP et al. 2020 ESC Guidelines for the management of acute coronary syndromes in patients presenting without persistent ST-segment elevation. Eur Heart J. 2021;42(14):1289-1367.

[2]Ibanez B et al. 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation. Eur Heart J. 2018;39(2):119-177.

[3]Thygesen K et al. Fourth Universal Definition of Myocardial Infarction (2018). J Am Coll Cardiol. 2018;72(18):2231-2264.

[4]Amsterdam EA et al. 2014 AHA/ACC Guideline for the Management of Patients with Non-ST-Elevation Acute Coronary Syndromes. J Am Coll Cardiol. 2014;64(24):e139-e228.

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.

ACUTE CORONARY SYNDROME

Definition

Word Breakdown

Abbreviations

Synonyms & Variants

Category-Specific Context

Clinical Context & Usage

Primary Causes & Pathophysiology

Drug-Induced Causes

Epidemiology

Red Flags & Triage ★

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

URGENT EVALUATION TRIGGERS

Contraindications & Precautions

CONTRAINDICATIONS

SPECIAL PRECAUTIONS

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Confused With (LASA & DDx) ★

Clinical Pearls

Example Usage & SOAP

Classifications & Scoring

Killip Classification

GRACE Score

TIMI Risk Score (UA/NSTEMI)

HEART Score

Prognosis

SHORT-TERM OUTCOME

LONG-TERM PROGNOSIS

Related Terms

References & Coding