Acute coronary syndromes

Overview

ACS spans unstable angina (UA), NSTEMI, and STEMI - all caused by acute reduction in coronary flow from plaque rupture and thrombosis. The ECG and troponin distinguish them and drive divergent management.

Classification

ACS classification
FeatureUANSTEMISTEMI
ECGNormal or ST depression / T-wave changesNormal or ST depression / T-wave changesST elevation ≥1 mm (≥2 mm precordial) in ≥2 contiguous leads, or new LBBB
TroponinNo riseRise (+/- fall)Rise (+/- fall)
Myocardial necrosisAbsentPresentPresent (transmural)
Reperfusion urgencyRisk-stratify; early invasive or conservativeRisk-stratify (GRACE score); angiography within 72 h if high-riskImmediate primary PCI within 120 min

Feature	UA	NSTEMI	STEMI
ECG	Normal or ST depression / T-wave changes	Normal or ST depression / T-wave changes	ST elevation ≥1 mm (≥2 mm precordial) in ≥2 contiguous leads, or new LBBB
Troponin	No rise	Rise (+/- fall)	Rise (+/- fall)
Myocardial necrosis	Absent	Present	Present (transmural)
Reperfusion urgency	Risk-stratify; early invasive or conservative	Risk-stratify (GRACE score); angiography within 72 h if high-risk	Immediate primary PCI within 120 min

Presentation

•Central crushing/pressure chest pain - radiating to left arm, jaw, or neck

•Diaphoresis, nausea/vomiting (especially inferior MI - vagal activation), dyspnoea, palpitations

•Atypical presentations - women (fatigue, nausea, back/jaw pain), diabetics (silent MI - autonomic neuropathy), elderly (confusion, breathlessness)

🚨
Red flag signs of haemodynamic compromise: hypotension (systolic <90 mmHg), new S3/pulmonary oedema (acute LV failure), new pansystolic murmur (papillary muscle rupture or VSD), raised JVP + clear lungs + hypotension (right ventricular infarction).

Investigations

🥇 First-line

•12-lead ECG - within 10 minutes of arrival; identifies STEMI vs NSTEMI/UA

•High-sensitivity troponin (hsTn) - at presentation and 1-2 h (or 3 h with standard assay); rise and/or fall pattern confirms myocardial injury

•FBC, U&E, glucose, lipid profile, renal function; chest X-ray (pulmonary oedema, widened mediastinum); continuous cardiac monitoring

🏆 Gold standard

•Coronary angiography - defines anatomy, identifies culprit lesion, enables PCI in same procedure

🥈 Second-line

•Echocardiogram - LV function, wall motion abnormalities, mechanical complications

•GRACE score for NSTEMI/UA risk stratification - score predicting >3% 6-month mortality = high-risk → angiography within 72 hours

🎯
ECG territory localisation: anterior (V1-V4) = LAD; inferior (II, III, aVF) = RCA; lateral (I, aVL, V5-V6) = LCx. Posterior MI = ST depression + tall R waves in V1-V3 (mirror image) - commonly missed.

Differential diagnosis

•Aortic dissection - tearing pain radiating to back, pulse differential, widened mediastinum; thrombolytics absolutely contraindicated

•Acute pericarditis - sharp pleuritic pain relieved leaning forward, saddle-shaped ST elevation with PR depression, pericardial rub

•Pulmonary embolism - pleuritic pain, dyspnoea, sinus tachycardia, S1Q3T3, elevated D-dimer

•Takotsubo cardiomyopathy - emotional trigger, post-menopausal women, apical ballooning on echo, mimics anterior STEMI

⚠️
Before thrombolytics for suspected STEMI, always consider aortic dissection - RCA ostium occlusion by dissection can produce inferior ST elevation. Tearing back pain or widened mediastinum on CXR → urgent CT aortogram; thrombolytics are contraindicated.

Management

•All ACS - immediate: aspirin 300 mg orally + P2Y12 inhibitor (ticagrelor 180 mg or clopidogrel); IV morphine for pain; sublingual GTN if BP adequate; oxygen only if SpO2 <94%

•STEMI - primary PCI within 120 minutes of first medical contact (door-to-balloon time); if PCI not available within 120 min → thrombolysis

•NSTEMI/UA high-risk (GRACE >3%) - early invasive angiography within 72 hours

•Secondary prevention on discharge: dual antiplatelet therapy + high-intensity statin + ACE inhibitor + beta-blocker ('SAAB' regimen)

•Cardiac rehabilitation referral for all patients; annual influenza vaccination; driving restriction - at least 1 week after successful PCI for STEMI (group 1 licence)

Complications

•VF (early, <24 h) - leading cause of prehospital death; requires immediate defibrillation

•Cardiogenic shock (early) - >40% LV loss; mortality >50%; consider mechanical circulatory support

•Papillary muscle rupture (2-7 days) - acute severe mitral regurgitation; loud pansystolic murmur + haemodynamic collapse; surgical emergency

•Ventricular septal defect (2-7 days) - new harsh pansystolic murmur + haemodynamic deterioration; urgent repair

•LV free wall rupture (3-5 days) - cardiac tamponade; more common after thrombolysis than primary PCI

•LV aneurysm (weeks-months) - persistent ST elevation post-MI; risk of mural thrombus and systemic embolism

•Dressler syndrome (2-10 weeks) - autoimmune pericarditis; pleuritic pain, fever, pericardial rub, raised inflammatory markers; treat with NSAIDs + colchicine

💡
Complete heart block is a recognised complication of inferior MI (RCA occlusion affecting the AV node) - monitor closely and have temporary pacing available.