ST-elevation myocardial infarction (STEMI)

Overview

STEMI = complete, persistent coronary occlusion causing transmural (full-thickness) myocardial necrosis. Irreversible cell death begins within 20-40 minutes; ~half of salvageable myocardium is lost in the first hour.

Presentation

•Central chest pain - severe, crushing/heavy ('elephant on chest'), radiating to left arm, jaw, neck, or back

•Diaphoresis - cold, clammy sweat (sympathetic activation)

•Nausea/vomiting - especially inferior STEMI (vagal stimulation)

•Dyspnoea - reduced cardiac output/early pulmonary oedema

•Atypical - epigastric pain, fatigue, silent MI; common in elderly, diabetic, and female patients

⚠️
Inferior STEMI (RCA occlusion): classically causes nausea/vomiting and bradycardia/heart block (RCA supplies SA and AV nodes). Always perform right-sided leads (V3R, V4R) - RV involvement contraindicates nitrates.

Investigations

🥇 First-line

•12-lead ECG - within 10 minutes of arrival; drives immediate management. Do NOT wait for troponin before activating the cath lab

•Troponin (high-sensitivity) - rises 3-6 hours after onset; take on arrival and repeat at 3-6 hours

•CXR - pulmonary oedema, exclude aortic dissection/pneumothorax; do not delay reperfusion

•U&E/eGFR - essential before contrast for angiography; FBC, glucose/HbA1c, lipid profile

🏆 Gold standard

•coronary angiography (+/- PCI) - defines culprit lesion and allows immediate intervention

Differential Diagnosis

•Aortic dissection - tearing pain radiating to back, unequal BPs, widened mediastinum; must exclude before thrombolysis (absolutely contraindicated)

•Pericarditis - saddle-shaped ST elevation in multiple non-contiguous leads, PR depression, pleuritic/positional pain, young patients

•PE - pleuritic pain, dyspnoea, S1Q3T3 on ECG, raised D-dimer

•Takotsubo cardiomyopathy - post-stress, postmenopausal women, apical ballooning on echo, unobstructed coronaries

•Benign early repolarisation - young men, J-point notching, no evolutionary ECG changes, no symptoms; diagnosis of exclusion

Management

Step 1 · Immediate pharmacological treatment
1Aspirin 300mg oral - always, unless contraindicated
2Ticagrelor 180mg oral (or prasugrel 60mg) - P2Y12 inhibitor for dual antiplatelet therapy
3Unfractionated heparin IV - anticoagulation before/during PCI
4Morphine - for pain; note may delay oral antiplatelet absorption
5Oxygen - only if SpO2 <94%; routine high-flow oxygen is harmful
6Nitrates - avoid if RV infarction, hypotension, or recent PDE5 inhibitor use
↓
Step 2 · Reperfusion strategy
1Primary PCI is the preferred reperfusion strategy - door-to-balloon time target <90 minutes
2If primary PCI not available within 120 minutes of first medical contact, give fibrinolysis (e.g. tenecteplase)
↓
Step 3 · Secondary prevention (on discharge)
1Aspirin lifelong + ticagrelor or clopidogrel for 12 months (dual antiplatelet)
2Beta-blocker (e.g. bisoprolol) - reduces mortality and arrhythmia risk
3ACE inhibitor (e.g. ramipril) - especially if reduced LVEF, heart failure, or diabetes
4Atorvastatin 80mg - high-intensity statin regardless of baseline cholesterol
5Cardiac rehabilitation

🧠
MONA mnemonic: Morphine (pain relief, but delays antiplatelet absorption), Oxygen (only if SpO2 <94%), Nitrates (avoid in RV infarction/hypotension), Aspirin (always). Apply critically, not reflexively.

Complications

STEMI complications by timing
ComplicationTimingKey feature
VF/VTHours (early)Most common cause of pre-hospital death
Cardiogenic shockEarlySBP <90 mmHg + hypoperfusion; large anterior STEMI; high mortality
Heart blockEarlyEspecially inferior STEMI (RCA supplies SA/AV nodes)
Free wall ruptureDays 2-7Sudden collapse, tamponade physiology; usually fatal
VSDDays 2-7New harsh pansystolic murmur at left sternal edge; urgent surgical repair
Acute MRDays 2-7Papillary muscle rupture; new systolic murmur, acute pulmonary oedema; urgent surgery
Dressler syndrome2-10 weeksAutoimmune pericarditis; pleuritic pain, fever, rub; treat with NSAIDs + colchicine
LV aneurysmWeeks-monthsPersistent ST elevation; risk of thrombus (anticoagulate) and arrhythmias

Complication	Timing	Key feature
VF/VT	Hours (early)	Most common cause of pre-hospital death
Cardiogenic shock	Early	SBP <90 mmHg + hypoperfusion; large anterior STEMI; high mortality
Heart block	Early	Especially inferior STEMI (RCA supplies SA/AV nodes)
Free wall rupture	Days 2-7	Sudden collapse, tamponade physiology; usually fatal
VSD	Days 2-7	New harsh pansystolic murmur at left sternal edge; urgent surgical repair
Acute MR	Days 2-7	Papillary muscle rupture; new systolic murmur, acute pulmonary oedema; urgent surgery
Dressler syndrome	2-10 weeks	Autoimmune pericarditis; pleuritic pain, fever, rub; treat with NSAIDs + colchicine
LV aneurysm	Weeks-months	Persistent ST elevation; risk of thrombus (anticoagulate) and arrhythmias

Prognosis

•In-hospital mortality ~5-7% with primary PCI (down from 10-15% pre-PCI era)

•Killip classification - Class I (no HF) <5% mortality; Class IV (cardiogenic shock) >80% mortality

•Poor prognostic features - anterior > inferior infarct, delayed reperfusion, reduced LVEF, older age, diabetes, renal impairment

•Echo pre-discharge to assess LVEF - if LVEF <35%, consider ICD after 40 days

ECG Interpretation

•STEMI criteria - ST elevation in ≥2 contiguous leads: >2mm in chest leads or >1mm in limb leads

•New LBBB with ischaemic symptoms = STEMI equivalent; treat with same urgency

•Posterior STEMI - ST depression in V1-V3 (mirror image); confirm with posterior leads V7-V9 (ST elevation >0.5mm diagnostic); suspect with dominant R waves + ST depression in V1-V2

Coronary territory - culprit vessel and ECG leads
WallCulprit vesselECG leads
AnteriorLADV1-V4
LateralLCxI, aVL, V5-V6
InferiorRCAII, III, aVF
PosteriorRCA/LCxV7-V9 (ST depression V1-V3)

Wall	Culprit vessel	ECG leads
Anterior	LAD	V1-V4
Lateral	LCx	I, aVL, V5-V6
Inferior	RCA	II, III, aVF
Posterior	RCA/LCx	V7-V9 (ST depression V1-V3)