Key Facts

STEMI is the most severe manifestation of acute coronary syndrome, caused by complete occlusion of a coronary artery by thrombus superimposed on a ruptured or eroded atherosclerotic plaque. This leads to transmural myocardial infarction requiring emergency reperfusion therapy.

Epidemiology

• ~30,000 STEMI admissions per year in England
• Male:female ratio ~3:1
• Peak incidence: men 55-64, women 65-74
• In-hospital mortality: ~7% (improved from >20% in pre-PCI era)
• UK has established PPCI networks providing 24/7 access in most regions

Aetiology

• Atherosclerotic plaque rupture/erosion with complete thrombotic occlusion (>95%)
• Rare: coronary spasm, spontaneous coronary artery dissection (SCAD), coronary embolism, coronary vasculitis

Pathophysiology

• Complete coronary occlusion causes transmural ischaemia
• Myocardial necrosis begins within 20-40 minutes and progresses as a wavefront from endocardium to epicardium
• Irreversible damage complete by ~6 hours without reperfusion
• Area of necrosis depends on: vessel occluded, collateral circulation, duration of occlusion, myocardial oxygen demand
• LAD occlusion → anterior wall (largest territory, worst prognosis)
• RCA occlusion → inferior wall (may include RV infarction)
• LCx occlusion → lateral/posterior wall

Typical Presentation

• Severe, prolonged (>20 minutes) central crushing chest pain
• Not relieved by rest or GTN
• Associated with sweating, nausea, vomiting, dyspnoea
• Sense of impending doom
• Pain radiation to left arm, jaw, neck

Territory-Specific Features

• Anterior STEMI (LAD): chest pain, anterior ST elevation (V1-V6), risk of cardiogenic shock
• Inferior STEMI (RCA): inferior ST elevation (II, III, aVF), may have bradycardia, nausea, RV involvement
• Lateral STEMI (LCx): lateral ST elevation (I, aVL, V5-V6)
• RV infarction: hypotension, elevated JVP, clear lung fields (give fluids, avoid nitrates)

Complications

• Early (0-48h): VF, VT, heart block, cardiogenic shock
• Subacute (days-weeks): papillary muscle rupture (acute MR), VSD, free wall rupture/tamponade, mural thrombus
• Late (weeks-months): Dressler syndrome, LV aneurysm, heart failure, recurrent ischaemia

Red Flags

• Cardiogenic shock (hypotension, oliguria, cold peripheries)
• New pansystolic murmur (VSD or acute MR)
• Pericardial friction rub with haemodynamic compromise (free wall rupture)
• Persistent VT/VF

Bedside

• 12-lead ECG: within 10 minutes of arrival
  • ST elevation ≥2mm in V1-V6 or ≥1mm in limb leads
  • Hyperacute T waves (earliest sign)
  • Reciprocal ST depression
  • New LBBB with appropriate clinical context
  • Posterior MI: ST depression V1-V3, ST elevation in V7-V9 (posterior leads)
• Continuous cardiac monitoring
• Pulse oximetry

Bloods

• High-sensitivity troponin: elevated (but do NOT wait for result before activating PPCI)
• FBC, U&Es, glucose, lipids: baseline
• Coagulation screen: before anticoagulation
• Group and save: in case of emergency surgery

Imaging

• Echocardiography: regional wall motion abnormalities, LV function, mechanical complications
• Coronary angiography: diagnostic and therapeutic (PPCI)
• Chest X-ray: pulmonary oedema (do not delay reperfusion)

Special Tests

• Cardiac MRI: viability assessment, infarct size, complications (if stable post-PCI)
• LV angiography: during cardiac catheterisation

Non-pharmacological

• Call 999: pre-hospital ECG and PPCI pathway activation
• Continuous monitoring in CCU/ICU
• Oxygen only if SpO₂ <94%

Pharmacological

Pre-PCI loading:

• Aspirin 300mg (chewed)
• Prasugrel 60mg loading (preferred for STEMI going to PPCI; or ticagrelor 180mg)
• Unfractionated heparin (70-100 IU/kg bolus) during PCI
• Morphine 2-5mg IV + metoclopramide 10mg IV for pain/nausea
• Sublingual GTN if SBP >90 mmHg (avoid in RV infarction)

Thrombolysis (if PPCI not available within 120 min):

• Tenecteplase IV bolus (weight-adjusted: 30-50mg)
• Alteplase 15mg bolus then infusion (alternative)
• Plus enoxaparin or UFH
• Rescue PCI if ST elevation persists 60-90 min after thrombolysis

Post-MI medications:

• DAPT: aspirin 75mg OD + ticagrelor 90mg BD (or prasugrel 10mg OD) for 12 months
• Atorvastatin 80mg OD
• ACE inhibitor: ramipril 1.25-10mg OD (start within 24 hours if stable)
• Beta-blocker: bisoprolol 1.25-10mg OD (titrate up)
• Eplerenone 25-50mg OD: if EF ≤40% and HF or diabetes (EPHESUS trial)
• Aldosterone antagonist added if signs of HF (EPHESUS trial)

Landmark trials:

• ISIS-2: aspirin + streptokinase reduced mortality
• GUSTO-I: tPA superior to streptokinase
• DANAMI-2: PPCI superior to thrombolysis
• EPHESUS: eplerenone post-MI with LV dysfunction reduced mortality

Surgical/Interventional

• Primary PCI: drug-eluting stent placement (standard of care)
• CABG: if PCI not feasible, failed PCI, or multivessel disease
• Mechanical circulatory support: IABP or Impella for cardiogenic shock
• ICD: if EF ≤35% at 40 days post-MI despite optimal medical therapy

Referral Criteria

• All STEMI: immediate PPCI pathway activation
• Post-STEMI: cardiac rehabilitation referral
• EF ≤35%: consider ICD referral at 40 days

• 30-day mortality: ~8-10% overall, <5% with timely PPCI
• 1-year mortality: ~12-15%
• Anterior STEMI: highest mortality (~12%), largest infarct size
• Inferior STEMI: better prognosis (~5% mortality) unless complicated by RV involvement
• Cardiogenic shock: mortality ~40-50% despite intervention
• Post-MI heart failure: significant impact on long-term survival
• Modern PPCI era: 5-year survival ~85-90%
• Late cardiac rupture risk: ~1-2% in first week post-MI

ECG Territory Localisation

Reperfusion Targets