Key Facts

Acute coronary syndromes result from acute myocardial ischaemia, usually due to coronary atherosclerotic plaque rupture with thrombosis. Rapid diagnosis and treatment save lives and preserve myocardium. The UK has well-established primary PCI networks.

Epidemiology

ACS affects approximately 100,000 people per year in England. STEMI accounts for approximately 30% and NSTEMI/UA for 70%. STEMI 30-day mortality has fallen to approximately 7% with primary PCI. NSTEMI 30-day mortality is approximately 5% but 1-year mortality may exceed STEMI due to older age and more comorbidities.

Aetiology

• Plaque rupture/erosion: Most common mechanism — exposes thrombogenic subendothelial matrix
• Risk factors: Smoking, hypertension, diabetes, dyslipidaemia, family history, obesity, age, male sex
• Type 2 MI: Myocardial oxygen supply-demand mismatch (sepsis, anaemia, tachyarrhythmia)
• Other causes: Coronary spasm (Prinzmetal's), coronary dissection (young women, pregnancy), cocaine

Pathophysiology

STEMI: Complete thrombotic occlusion of a coronary artery → transmural ischaemia → myocardial necrosis begins within 20 minutes → irreversible damage progresses over 6-12 hours (wavefront phenomenon). Time is muscle — every 30-minute delay in reperfusion increases mortality.

NSTEMI: Partial/intermittent occlusion or distal embolisation → subendocardial ischaemia → troponin release. Spectrum from unstable plaque with minimal necrosis to extensive subendocardial infarction.

Typical ACS Presentation

• Central chest pain/tightness/heaviness — may radiate to left arm, jaw, back, epigastrium
• Associated with sweating, nausea, dyspnoea, palpitations
• Pain at rest lasting >20 minutes (STEMI); may be crescendo/at rest (unstable angina/NSTEMI)

Atypical Presentations (Common in Elderly, Women, Diabetics)

• Epigastric pain, isolated dyspnoea, syncope, confusion
• Silent MI — particularly in diabetic neuropathy
• Painless troponin elevation — consider type 2 MI

ECG Classification

• STEMI: ≥2mm ST elevation in V1-V3, or ≥1mm in 2 contiguous limb leads; new LBBB
• NSTEMI: ST depression, T-wave inversion, or normal ECG with positive troponin
• Unstable angina: ECG changes without troponin rise

Red Flags

• ST elevation on ECG — activate primary PCI pathway immediately
• Cardiogenic shock (hypotension, pulmonary oedema, poor perfusion) — highest mortality, may need mechanical support
• Acute mitral regurgitation, VSD, or free wall rupture — mechanical complications requiring emergency surgery
• Ventricular arrhythmias (VT/VF) — immediate defibrillation

Bedside

• 12-lead ECG: Within 10 minutes of presentation — repeat at 15-30 min if initial normal and pain continues
• Observations: BP (both arms), HR, SpO2, RR
• Pain assessment: Onset, character, radiation, severity

Bloods

• High-sensitivity troponin (hs-cTnI or hs-cTnT): At presentation and 3 hours (or 0 and 1 hour with validated rapid rule-out protocol)
• FBC: Anaemia (type 2 MI), baseline
• U&Es: Renal function (pre-PCI, drug dosing)
• Glucose/HbA1c: Diabetes screening
• Lipid profile: Within 24 hours (most accurate before acute phase response)
• Coagulation: Pre-anticoagulation

Imaging

• CXR: Pulmonary oedema, mediastinal widening (dissection)
• Echocardiography: Assess LV function, regional wall motion abnormalities, mechanical complications
• Coronary angiography: Primary PCI for STEMI; within 72 hours for NSTEMI (within 24h if high-risk GRACE >140)

Special Tests

• GRACE score: Risk stratification for NSTEMI/UA — guides timing of angiography and intensity of antithrombotic therapy
• CT coronary angiography: For low-intermediate risk chest pain with indeterminate troponin

Non-pharmacological

• Primary PCI for STEMI: Within 120 minutes of first medical contact — activate catheter lab immediately
• Oxygen: Only if SpO2 <94% (DETO2X-AMI trial — routine O2 not beneficial in normoxic patients)
• Cardiac monitoring: Continuous until diagnosis established

Pharmacological

Immediate (all ACS):

• Aspirin 300mg PO (chewed for rapid absorption)
• GTN: Sublingual 400mcg spray (if SBP >90mmHg; avoid in RV infarction)
• Morphine 2-5mg IV: If ongoing pain (with metoclopramide 10mg IV antiemetic) — use cautiously

STEMI — Primary PCI pathway:

• Aspirin 300mg + ticagrelor 180mg (or prasugrel 60mg if ticagrelor contraindicated)
• Unfractionated heparin during PCI (70-100 units/kg IV)
• GP IIb/IIIa inhibitor (abciximab or eptifibatide) — if needed during PCI
• If PCI not available within 120 min: Thrombolysis (alteplase, tenecteplase, or reteplase)

NSTEMI/UA:

• Aspirin 300mg + ticagrelor 180mg loading then 90mg BD (or clopidogrel 300mg loading then 75mg OD)
• Fondaparinux 2.5mg SC OD (or LMWH if proceeding to PCI within 24h)
• Angiography timing guided by GRACE score: >140 = within 24h; 109-140 = within 72h; <109 = conservative or elective

Secondary prevention (all ACS):

• DAPT for 12 months (aspirin 75mg + ticagrelor 90mg BD)
• Statin: Atorvastatin 80mg OD (start immediately)
• ACEi: Ramipril 1.25-10mg OD (start within 24h if LV impairment)
• Beta-blocker: Bisoprolol 1.25-10mg OD
• Cardiac rehabilitation referral

Surgical/Interventional

• Primary PCI: Drug-eluting stent placement
• Thrombolysis: If PCI not available within 120 min — tenecteplase weight-adjusted IV bolus
• CABG: For left main stem or triple-vessel disease (especially with diabetes)
• Mechanical support: IABP or Impella for cardiogenic shock

Referral Criteria

• STEMI — immediate primary PCI referral (call catheter lab directly)
• NSTEMI with GRACE >140 — urgent angiography within 24h
• Cardiogenic shock — urgent cardiology/cardiac surgery
• Post-MI heart failure — cardiology for optimisation and device assessment

• STEMI primary PCI mortality: ~5-7% at 30 days; significantly better than thrombolysis
• NSTEMI mortality: ~5% at 30 days; ~12% at 1 year
• Door-to-balloon time <90 min: Associated with best outcomes
• Risk factors for poor outcome: Age, diabetes, renal failure, heart failure, anterior STEMI, late presentation
• Long-term: 10-year survival post-MI ~70% with optimal secondary prevention
• Cardiac rehabilitation: Reduces mortality by 20-25%

GRACE Score Risk Stratification

ECG Localisation of STEMI

Key ACS Trials