About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- ACS = spectrum from unstable angina → NSTEMI → STEMI, distinguished by ECG and troponin
- STEMI = ST elevation + positive troponin → emergent PCI (or thrombolysis if PCI not available within 120 min)
- NSTEMI = troponin rise without persistent ST elevation → risk stratify (GRACE score) → angiography within 72 h
- All ACS: dual antiplatelet therapy (aspirin + ticagrelor/prasugrel), fondaparinux, and high-dose statin
- Red flags: ongoing chest pain, haemodynamic instability, acute pulmonary oedema, cardiac arrest
Overview
Acute coronary syndromes encompass a spectrum of presentations caused by sudden reduction in coronary blood flow. The unifying pathology is usually atherosclerotic plaque rupture or erosion with superimposed thrombus formation. Classification depends on ECG findings and troponin dynamics: STEMI shows persistent ST elevation and is a clinical emergency requiring immediate reperfusion; NSTEMI shows troponin rise without persistent ST elevation; unstable angina presents with ischaemic symptoms at rest or crescendo pattern but without troponin rise.
Epidemiology
Coronary heart disease remains the single largest cause of death in the UK. Approximately 100,000 hospital admissions per year are for ACS. STEMI accounts for roughly 30–40% of ACS presentations. Key risk factors include smoking, hypertension, diabetes, hypercholesterolaemia, family history of premature coronary disease, obesity, and chronic kidney disease. Incidence increases sharply with age, and men are affected more often than women before menopause.
Clinical Features
Symptoms
Central crushing chest pain radiating to left arm, neck, or jaw
Pain at rest or crescendo pattern (previously stable angina worsening)
Dyspnoea and sweating (diaphoresis)
Nausea and vomiting
Syncope or presyncope
Atypical presentations: epigastric pain, isolated dyspnoea, or "silent" MI (especially in elderly, diabetic patients, and women)
Signs
Haemodynamic instability: hypotension, tachycardia, or bradycardia
Signs of acute heart failure: raised JVP, bibasal crackles, S3 gallop
Diaphoresis, pallor, distress
New murmur (papillary muscle rupture → acute mitral regurgitation)
May be completely normal on examination
Investigations
First-line
12-lead ECGWithin 10 minutes. Look for ST elevation (≥1 mm in 2+ contiguous leads, ≥2 mm in V1–V3), ST depression, T-wave inversion, new LBBB
High-sensitivity troponinAt presentation and at 3 hours (or 1 hour if using 0/1h hs-cTn algorithm). Rising/falling pattern confirms acute myocardial injury
BloodsFBC, U&Es, glucose, lipid profile, coagulation screen
Second-line
Chest X-rayPulmonary oedema, widened mediastinum (to exclude aortic dissection)
EchocardiogramRegional wall motion abnormalities, LV function assessment, mechanical complications
GRACE scoreRisk stratification for NSTEMI/UA — determines urgency of angiography
Specialist
Coronary angiographyDefinitive anatomical assessment — emergent in STEMI, within 72 h for NSTEMI (within 24 h if high risk)
CT coronary angiogramMay be used in low-risk chest pain to exclude significant CAD
1
Immediate (all ACS)
- Aspirin 300 mg loading dose (chewed)
- GTN sublingual (unless hypotensive or RV infarct)
- Morphine IV for pain unresponsive to GTN (with antiemetic)
- Oxygen only if SpO₂ < 94%
- Continuous cardiac monitoring
2
STEMI pathway
- Primary PCI is the gold standard — door-to-balloon time < 90 min
- If PCI not available within 120 min of first medical contact → thrombolysis (tenecteplase)
- Dual antiplatelet: aspirin + prasugrel (or ticagrelor if prasugrel contraindicated)
- Anticoagulation: unfractionated heparin during PCI
- Consider GP IIb/IIIa inhibitor during PCI if high thrombus burden
3
NSTEMI / Unstable angina pathway
- Fondaparinux 2.5 mg SC OD (or UFH if eGFR <20 or angiography within 24 h)
- Dual antiplatelet: aspirin + ticagrelor (or clopidogrel if high bleeding risk)
- Risk stratify with GRACE score → determines timing of angiography
- High risk (GRACE >140): angiography within 24 h
- Intermediate risk (GRACE 109–140): angiography within 72 h
- Low risk: non-invasive functional testing or conservative management
4
Secondary prevention (all ACS on discharge)
- Dual antiplatelet therapy for 12 months (aspirin indefinitely + ticagrelor/prasugrel/clopidogrel)
- High-dose statin: atorvastatin 80 mg
- ACE inhibitor (or ARB) — especially if LVEF ≤40%, diabetes, or hypertension
- Beta-blocker — especially if LVEF ≤40%
- Cardiac rehabilitation referral
- Lifestyle: smoking cessation, diet, exercise, weight management
Complications
- Arrhythmias: VF/VT (commonest cause of early death), heart block (especially inferior MI), atrial fibrillation
- Heart failure: Acute LV failure, cardiogenic shock (Killip class IV)
- Mechanical: Papillary muscle rupture (acute MR), ventricular septal defect, free wall rupture (cardiac tamponade)
- Pericarditis: Early (within 48 h) or Dressler syndrome (2–10 weeks post-MI, autoimmune)
- Thromboembolism: LV mural thrombus → systemic embolisation
- Recurrence: Re-infarction, in-stent restenosis/thrombosis
UKMLA Exam Tips
- 1A question showing chest pain + ST elevation + positive troponin = STEMI → answer is always primary PCI unless they explicitly say PCI is unavailable (then thrombolysis)
- 2Know the difference between GRACE and TIMI scores — NICE recommends GRACE for risk stratification
- 3Prasugrel is preferred over ticagrelor for STEMI going to PCI; ticagrelor is preferred for NSTEMI
- 4Fondaparinux is first-line anticoagulant for NSTEMI (not enoxaparin) per NICE
- 5If asked about a "new LBBB with chest pain" — treat as STEMI equivalent
- 6Dressler syndrome = pericarditis + fever + raised ESR appearing 2–10 weeks after MI — treat with NSAIDs, not antibiotics
practicetest your knowledge on acute coronary syndromesApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — cardiovascular and beyond.
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