Non-ST-elevation acute coronary syndrome (NSTE-ACS)

Overview

•NSTE-ACS = unstable angina (no myocyte necrosis) + NSTEMI (necrosis confirmed by troponin rise)

•Mechanism: plaque rupture/erosion → partial/intermittent thrombus → subendocardial ischaemia (cf. STEMI: complete occlusion → transmural necrosis)

•ECG cannot distinguish NSTEMI from unstable angina - troponin is the differentiating test

⚠️

A normal ECG does not exclude NSTE-ACS. Serial ECGs are essential if the first is normal.

Presentation

•Chest pain - central/left-sided, pressure/tightness/heaviness, occurring at rest or minimal exertion

•Radiation - jaw, neck, left arm, shoulders, back

•Diaphoresis, dyspnoea, nausea/vomiting, presyncope

•Atypical presentations - women, older patients, and diabetics often present without chest pain; may be dyspnoea, fatigue, epigastric discomfort, or weakness alone

🎯

An atypical presentation does not mean a low-risk patient - maintain a high index of suspicion in women, elderly, and diabetics.

Investigations

🥇 First-line

•12-lead ECG immediately - ST depression, T-wave inversion, new LBBB; repeat serially if first normal

•High-sensitivity troponin I or T - on arrival and repeated at 1-3 hours; rise and/or fall pattern confirms NSTEMI vs unstable angina

•GRACE score - risk stratification using age, HR, SBP, creatinine, Killip class, cardiac arrest, ST deviation, elevated enzymes; predicts 6-month mortality and directly determines angiography timing

•Chest X-ray - pulmonary oedema, widened mediastinum (exclude dissection), cardiomegaly

•Bloods - FBC, U&Es (baseline before ACEi; guide fondaparinux use in renal impairment), LFTs, glucose, HbA1c, fasting lipids

🏆 Gold standard

•Coronary angiography - direct visualisation of coronary anatomy; allows immediate PCI

🥈 Second-line

•Echocardiogram - once stable; LV function, regional wall motion abnormalities, mechanical complications

Management

•Immediate antiplatelet: aspirin 300 mg oral loading - give immediately on suspected ACS

•Second antiplatelet: ticagrelor 180 mg oral loading (preferred); use clopidogrel 300 mg if high bleeding risk or on oral anticoagulation

•Antithrombin: fondaparinux SC - preferred for NSTE-ACS not requiring immediate angiography (favourable bleeding profile); switch to unfractionated heparin (UFH) at time of PCI

•Analgesia/vasodilation: sublingual or IV GTN - relieves ischaemic pain, reverses vasospasm; IV morphine titrated to pain with antiemetic (metoclopramide or ondansetron)

•Oxygen: only if SpO2 <94% (target 94-98%; 88-92% in COPD) - routine high-flow oxygen not indicated and may be harmful in normoxic patients

⚠️

Do not give dual antiplatelet therapy before diagnosis is confirmed.

Complications

•Progression to STEMI - thrombus propagation causing complete occlusion; requires immediate reassessment

•Arrhythmias - VF, VT, complete heart block; reason for continuous monitoring

•Cardiogenic shock - extensive ischaemia causing pump failure; hypotension, pulmonary oedema, poor perfusion

•Mechanical complications - papillary muscle dysfunction (acute MR), VSD, free wall rupture; rare but life-threatening

🚨

New hypotension, worsening pulmonary oedema, new murmur, or loss of consciousness in NSTE-ACS = urgent reassessment for mechanical complications or cardiogenic shock - indication for immediate angiography regardless of GRACE score.

Secondary Prevention

•Aspirin 75 mg once daily indefinitely

•Second antiplatelet (ticagrelor 90 mg twice daily or clopidogrel 75 mg once daily) for 12 months

•Atorvastatin 80 mg once nightly - high-intensity statin for all post-MI patients regardless of baseline cholesterol

•ACE inhibitor (e.g. ramipril) titrated to maximum tolerated dose - reduces adverse cardiac remodelling; especially important with LV dysfunction

•Beta-blocker (e.g. bisoprolol) titrated to maximum tolerated dose - continue for 12 months post-MI; review ongoing use at 12 months

•Aldosterone antagonist (e.g. eplerenone) - indicated if clinical heart failure or LV ejection fraction ≤35% post-MI; monitor renal function and potassium (hyperkalaemia risk with ACEi)