Acute coronary syndrome is one of the highest-yield emergencies in UK exams, testing ECG interpretation, time-critical reperfusion decisions and secondary prevention in a single scenario. This guide covers the essentials to the current NICE standard (NG185). Follow current guidance and local protocols in practice; this reflects NICE guidance as of mid-2026.
The spectrum
ACS spans three diagnoses on a continuum: ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI) and unstable angina. The ECG and troponin separate them: ST elevation (or a new left bundle branch block) defines STEMI; a troponin rise without ST elevation indicates NSTEMI; ischaemic symptoms with a normal troponin suggest unstable angina. The underlying event in most ACS is rupture or erosion of an atherosclerotic plaque with thrombus formation; the classic risk factors — smoking, hypertension, diabetes, hyperlipidaemia, a family history and increasing age — are the same ones examiners expect you to elicit and to modify in secondary prevention.
Recognising STEMI on the ECG
Examiners expect confident ECG reading: ST elevation of at least 2 mm in two contiguous chest leads or 1 mm in two limb leads; a new left bundle branch block with chest pain treated as a STEMI; and the posterior MI trap — ST depression in V1 to V3 with tall R waves, where posterior leads (V7 to V9) reveal the elevation. Presentation is usually central, crushing chest pain radiating to the arm or jaw with sweating and nausea, but examiners reward awareness of atypical presentations — older people, those with diabetes and women may present with breathlessness, fatigue or epigastric discomfort rather than classic pain, and a silent infarction is easily missed. A normal initial troponin does not exclude evolving infarction, so serial sampling is used.
Initial management of any ACS
Give aspirin 300 mg, relieve pain (nitrates, and intravenous morphine with an antiemetic if severe), and give oxygen only if the patient is hypoxic — routine oxygen is no longer recommended, a common update point, since hyperoxia may be harmful and oxygen should be targeted to a saturation goal only in hypoxic patients. The pathway then diverges by type.
STEMI: reperfusion
STEMI is about reperfusion speed. Offer primary PCI if the patient presents within 12 hours of symptom onset and PCI can be delivered within 120 minutes of the time fibrinolysis could otherwise have been given; if not, give fibrinolysis. For primary PCI, NICE recommends prasugrel with aspirin in those not already taking an oral anticoagulant (weighing bleeding risk in those aged 75 and over), and clopidogrel with aspirin in those already anticoagulated. Complete revascularisation is offered for multivessel disease without cardiogenic shock, and drug-eluting stents are used. Knowing the territory from the ECG is a common requirement: inferior leads (II, III and aVF) point to the right coronary artery, anterior leads (V1 to V4) to the left anterior descending, and lateral leads (I, aVL, V5 and V6) to the circumflex.
NSTEMI and unstable angina: risk-stratify
Here the key tool is the GRACE score, which estimates six-month mortality and guides how aggressively to investigate. The risk assessment combines history, examination, ECG and bloods (troponin, creatinine, glucose, haemoglobin). Higher-risk patients — for example, a six-month mortality above 3% — are offered coronary angiography, with follow-on PCI if indicated, within 72 hours. Antiplatelet therapy is prasugrel or ticagrelor with aspirin where there is no separate anticoagulation indication — with prasugrel given only once the coronary anatomy is known and PCI intended — and clopidogrel with aspirin where anticoagulation is already indicated. Antithrombin cover is usually fondaparinux, unless immediate angiography is planned or bleeding risk is high.
Secondary prevention
After any MI, examiners expect the package: dual antiplatelet therapy (typically up to 12 months), a high-intensity statin (such as atorvastatin 80 mg), an ACE inhibitor (titrated, with renal monitoring), and a beta-blocker. Add an aldosterone antagonist where there is heart failure with a left ventricular ejection fraction of 40% or below. Assess left ventricular function in everyone after a STEMI, and refer to cardiac rehabilitation. Examiners also test the complications of MI, which include arrhythmias, heart failure and cardiogenic shock, mechanical complications such as papillary muscle or ventricular septal rupture, pericarditis, and the later Dressler's syndrome. Right ventricular infarction can accompany an inferior STEMI and is sensitive to nitrate-induced hypotension, so nitrates are used cautiously in that setting.
High-yield exam points and traps
- A new left bundle branch block with chest pain is a STEMI — treat it as such.
- Posterior MI: ST depression in V1 to V3 with tall R waves; look at V7 to V9.
- Oxygen only if hypoxic — not routine.
- GRACE guides NSTEMI: it predicts six-month mortality and the timing of angiography.
- Prasugrel in NSTEMI only once the anatomy is defined and PCI is intended.
- Secondary prevention is a high-intensity statin, dual antiplatelets, an ACE inhibitor and a beta-blocker — with an aldosterone antagonist if the ejection fraction is 40% or below.
A few common questions
What is the time target for primary PCI in STEMI? Within 120 minutes of when fibrinolysis could have been given, in a patient presenting within 12 hours of symptom onset; otherwise give fibrinolysis.
Which score risk-stratifies NSTEMI? The GRACE score, which estimates six-month mortality and guides the timing of angiography.
Is a new left bundle branch block significant? Yes — a new left bundle branch block with chest pain is managed as a STEMI.
What is the secondary prevention after an MI? Dual antiplatelet therapy, a high-intensity statin, an ACE inhibitor and a beta-blocker, plus an aldosterone antagonist if the ejection fraction is 40% or below.
How do you localise an MI on the ECG? Inferior changes (II, III, aVF) suggest the right coronary artery, anterior changes (V1 to V4) the left anterior descending, and lateral changes (I, aVL, V5 and V6) the circumflex.
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