Acute coronary syndromes - ST-elevation myocardial infarction (STEMI)
Description
- Complete thrombotic occlusion of an epicardial coronary artery -> transmural ischaemia
- Type 1 MI - plaque rupture/erosion + occlusive thrombus
- Time is muscle - necrosis starts ~20-30 min, largely complete by 6-12 h
- Wavefront spreads subendocardium -> epicardium
| Leads | Territory | Artery |
|---|---|---|
| II, III, aVF | Inferior | RCA (or LCx) |
| V1-V4 | Anteroseptal | LAD |
| I, aVL, V5-V6 | Lateral | LCx / diagonal |
| V1-V3 ST depression + tall R | Posterior | LCx / RCA |
| V4R ST elevation | RV | Proximal RCA |
Epidemiology
- Coronary disease remains a leading single cause of death in Australia
- STEMI as a share of ACS falling; NSTEMI rising with high-sensitivity troponin
- M>F, and ~10 yrs earlier in men
- Women - more atypical presentation, longer delays, worse outcomes
- Aboriginal and Torres Strait Islander Australians: IHD at younger age, higher mortality
Aetiopathogenesis
Mechanism
- Vulnerable plaque - thin fibrous cap, large lipid core, inflammation
- -> rupture or erosion
- -> platelet adhesion, activation, aggregation
- -> occlusive fibrin-rich thrombus
- -> transmural ischaemia -> necrosis
Non-atherosclerotic causes
- SCAD - young women, peripartum, fibromuscular dysplasia
- Coronary embolism - AF, endocarditis, prosthetic valve
- Vasospasm - cocaine, methamphetamine, Prinzmetal
- Arteritis, in-stent thrombosis, dissection extending to the ostium
Risk factors
- Modifiable - smoking, HTN, dyslipidaemia, diabetes, obesity, inactivity
- Non-modifiable - age, male sex, family history, CKD, chronic inflammatory disease
Diagnosis
ECG makes the diagnosis
- Ischaemic symptoms >20 min + new ST elevation in >=2 contiguous leads
| Leads | Threshold |
|---|---|
| V2-V3, men <40 | >=2.5 mm |
| V2-V3, men >=40 | >=2.0 mm |
| V2-V3, women | >=1.5 mm |
| All other leads | >=1.0 mm |
- New LBBB in the right clinical context
- V4R in every inferior STEMI; posterior leads if V1-V3 depression with tall R
LBBB or paced rhythm - Sgarbossa
- Concordant STE >=1 mm (5 points)
- ST depression >=1 mm in V1-V3 (3 points)
- Discordant STE >=5 mm (2 points)
- Score >=3 is ~98% specific for MI
Adjuncts
- Troponin - *do not wait for it; a normal troponin never delays reperfusion*
- Bedside echo if diagnosis uncertain or shock - RWMA, mechanical complication
Mimics - do not thrombolyse
- Pericarditis, early repolarisation, LVH, Brugada, LV aneurysm, Takotsubo, hyperkalaemia
Management
Immediate
- ECG within 10 min of first medical contact
- Aspirin 300 mg chewed
- O2 only if SpO2 <93% - routine O2 increases infarct size (AVOID)
- GTN for pain (contraindicated in RV infarct, severe AS, recent PDE5i), IV morphine if needed
Reperfusion - the whole decision
- Primary PCI if first-contact-to-device <=120 min
- Target <=90 min if already at a PCI-capable hospital
- Preferred regardless of time in cardiogenic shock, or if lysis contraindicated
- Fibrinolysis if PCI not achievable within 120 min
- Give within 30 min of arrival - tenecteplase, weight-adjusted
- Contraindicated: prior ICH, ischaemic stroke <6 months, active bleeding, recent major surgery/trauma, BP >=180/110
- Then transfer everyone for angiography at 3-24 h (pharmaco-invasive)
- Rescue PCI now if <50% ST resolution at 60-90 min, or instability
Antithrombotic
- DAPT: aspirin + ticagrelor or prasugrel after primary PCI
- Clopidogrel if fibrinolysis given, high bleeding risk, or on an anticoagulant
- Prasugrel contraindicated after stroke/TIA
- Parenteral anticoagulation peri-procedure - heparin or enoxaparin
Multivessel disease
- Stable: complete revascularisation, index procedure or within 1 month (COMPLETE)
- Cardiogenic shock: culprit lesion only (CULPRIT-SHOCK)
Complication-specific
- RV infarct: fluid load; avoid nitrates, diuretics, morphine - preload-dependent
- Cardiogenic shock: early revascularisation; IABP not routine (IABP-SHOCK II)
- Inferior MI bradycardia/AV block - atropine, temporary pacing; usually transient
Secondary prevention - start before discharge
- Aspirin indefinitely + P2Y12 for 12 months
- High-intensity statin +/- ezetimibe to target
- Beta blocker and ACEi/ARB - especially if EF reduced; MRA if EF <=40%
- Cardiac rehabilitation - mortality benefit, chronically under-referred
- Smoking cessation, BP, glycaemia, weight, exercise
- Reassess EF at 6-12 weeks for ICD candidacy
Associations
- The risk factor cluster - smoking, HTN, dyslipidaemia, diabetes, obesity
- SCAD - young women, peripartum, fibromuscular dysplasia
- Cocaine and methamphetamine use
- Chronic inflammatory disease - RA, SLE, psoriasis, HIV
- CKD
- Familial hypercholesterolaemia
- Depression post-MI - common, worsens adherence and outcomes
Natural history & complications
Early complications
- Arrhythmia - VF peaks in the first 4 h; AF; AV block
- Cardiogenic shock, acute pulmonary oedema
- Mechanical, days 3-7 - papillary muscle rupture (acute MR), VSD, free wall rupture
- New murmur + sudden deterioration = echo now
- Pericarditis, LV thrombus
Late
- HF from adverse remodelling
- LV aneurysm - persistent ST elevation
- Dressler's syndrome - weeks later
- Recurrent ischaemia, ventricular arrhythmia, SCD
Prognosis
- In-hospital mortality now low with timely reperfusion; substantially higher with shock
- Driven by infarct size, EF, time to reperfusion, age, renal function
- Women and Aboriginal and Torres Strait Islander Australians have worse outcomes
🔒
6 more sections, plus exam facts
Premium unlocks every note across every specialty, and the full exam fact library behind it.
Get premium access