PassFinals
Cardiovascular

ST-Elevation Myocardial Infarction (STEMI)

ST-elevation myocardial infarction (STEMI) is acute coronary occlusion, usually thrombus on a disrupted plaque, whose injury current appears as persistent regional ST elevation in a compatible ischaemic presentation.

In a nutshell

ST-elevation myocardial infarction (STEMI) is acute coronary occlusion shown by persistent regional ST elevation, and it is diagnosed on the ECG without waiting for troponin. Give aspirin 300 mg chewed, then reperfuse: primary percutaneous coronary intervention (PCI) if it can be delivered within 120 minutes of when fibrinolysis could have been given, otherwise fibrinolysis.

Classic presentation

Crushing central chest pain for an hour with sweating, nausea and vomiting, and ST elevation in leads II, III and aVF.

Key points

  • Confirming infarction needs a rise and/or fall in troponin with one value above the 99th-percentile upper reference limit, plus evidence of acute ischaemia.
  • Left ventricular hypertrophy, pericarditis, Brugada pattern and early repolarisation also displace the ST segment, so the tracing alone never makes the diagnosis.
  • ST elevation identifies who benefits from immediate reperfusion. It does not prove the artery is completely occluded or that necrosis is already full thickness.
  • Inferior changes in II, III and aVF usually mean the right coronary artery, anterior changes the left anterior descending, lateral changes the circumflex.
  • Reciprocal ST depression helps separate STEMI from pericarditis and early repolarisation, but it is not required for the diagnosis.
  • Presumed new left bundle branch block with a compatible presentation is managed on the STEMI pathway. Do not let the hunt for an old tracing delay treatment.
  • Anyone ineligible for any reperfusion therapy is still offered medical management.

First-line investigation

A 12-lead ECG within 10 minutes of first medical contact. Add right-sided leads V3R and V4R for inferior changes, and posterior leads V7 to V9 for ST depression in V1 to V3.

Management

The first ten minutes

  • ABCDE (airway, breathing, circulation, disability, exposure), IV access, rhythm and saturation monitoring, defibrillator to hand, and a 12-lead ECG within 10 minutes of first medical contact.5,2
  • Aspirin 300 mg orally, chewed or dispersed. Oxygen only if saturation is below 94%: target 94% to 98%, or 88% to 92% at risk of hypercapnic respiratory failure.3,6,1
  • Glyceryl trinitrate (GTN) sublingual, 1 tablet (500 or 600 micrograms) or 1 to 2 sprays of 400 micrograms, repeat at 5 minutes, maximum 3 doses.1,7
  • Severe pain: morphine 5 to 10 mg by slow IV injection at 1 to 2 mg/minute, or 2.5 to 5 mg if frail or elderly.8
  • Activate the STEMI network on the ECG alone. Do not wait for troponin, and examine for aortic dissection before any fibrinolytic.3,1

Reperfusion: primary PCI and its two clocks

  • Within 12 hours of symptom onset: primary PCI if it can be delivered within 120 minutes of when fibrinolysis could have been given. Otherwise fibrinolysis.3
  • Primary PCI: prasugrel 60 mg then 10 mg once daily with aspirin, or 5 mg once daily if under 60 kg or aged 75 and over.3,9
  • Already on an oral anticoagulant: clopidogrel 300 mg then 75 mg once daily with aspirin instead of prasugrel.3,10
  • Radial access: unfractionated heparin with a bailout glycoprotein IIb/IIIa inhibitor. Femoral: consider bivalirudin. Prefer radial, offer a drug-eluting stent, and give no lytic before the laboratory.3
  • Multivessel disease without shock: complete revascularisation, considering it during the index admission. With cardiogenic shock: consider culprit-vessel-only PCI at the index procedure.3

Fibrinolysis when PCI cannot be delivered in time

  • Tenecteplase IV over 10 seconds, within 6 hours of symptom onset. Dose 30 mg under 60 kg, rising 5 mg per 10 kg band to 50 mg at 90 kg and above.3,11
  • Alteplase alternative, accelerated myocardial infarction regimen: 15 mg IV bolus, then 0.75 mg/kg over 30 minutes, then 0.5 mg/kg over 60 minutes, maximum 100 mg.12
  • Give an antithrombin at the same time: enoxaparin 30 mg IV, then 1 mg/kg subcutaneously every 12 hours, maximum 100 mg per dose, for up to 8 days.3,13
  • Aged 75 and over: no IV bolus, and enoxaparin 750 micrograms/kg subcutaneously every 12 hours, maximum 75 mg per dose. Fondaparinux 2.5 mg IV then 2.5 mg subcutaneously daily is an alternative.13,14
  • Clopidogrel is the licensed second antiplatelet for medically treated STEMI eligible for lysis: 300 mg then 75 mg daily with aspirin for at least 4 weeks, no load over 75.15,6
  • Repeat the ECG 60 to 90 minutes after the lytic. Residual ST elevation means immediate angiography with follow-on PCI; never repeat the fibrinolytic.3

ECG patterns that hide an occlusion

  • New J-point elevation of 1 mm in two contiguous leads, except V2 to V3: 2.5 mm in men under 40, 2 mm from 40, 1.5 mm in women.2
  • Left bundle branch block (LBBB), right bundle branch block (RBBB) and ventricular pacing mask ST elevation. Concordant ST elevation of 1 mm in any lead suggests ischaemia.2
  • ST depression of 0.5 mm in V1 to V3 with an upright terminal T wave: record V7 to V9, where 0.5 mm of elevation confirms posterior occlusion.2
  • Inferior STEMI: record V3R and V4R. ST elevation of 0.5 mm there means right-ventricular infarction, which is preload dependent, so nitrates can drop the blood pressure.2

Failed reperfusion, shock and arrest

  • Recurrent ischaemia after lysis: immediate specialist cardiology advice and angiography with follow-on PCI if indicated. After successful lysis in a stable patient, consider angiography this admission.3
  • Cardiogenic shock within 12 hours: offer angiography with follow-on primary PCI. Beyond 12 hours with shock, consider angiography with a view to revascularisation.3
  • Cardiac arrest: start cardiopulmonary resuscitation under Resuscitation Council UK guidelines while expediting coronary reperfusion.5
  • Sudden hypotension, a new murmur, pulmonary congestion or a raised JVP: emergency echocardiography for a mechanical complication, with immediate cardiology and critical-care review.3

Before discharge

  • Assess left ventricular function in everyone who has had a STEMI, and nurse in a monitored bed with continued rhythm, blood-pressure and saturation monitoring after reperfusion.3,1
  • Aspirin 75 mg once daily indefinitely, with dual antiplatelet therapy for up to 12 months. Atorvastatin 80 mg once daily, started without delay.3,6,19,4
  • Ramipril 2.5 mg once daily once stable, titrated towards 10 mg once daily at 12 to 24 hour intervals in hospital. Continue indefinitely.3,17
  • Bisoprolol once stable. With reduced left ventricular ejection fraction (LVEF): 1.25 mg once daily titrated stepwise to 10 mg, indefinitely; otherwise consider stopping at 12 months.3,18
  • Heart failure with reduced LVEF: add an aldosterone antagonist licensed post-MI within 3 to 14 days, after the angiotensin-converting enzyme (ACE) inhibitor. Halve or stop it for hyperkalaemia.3
  • Target LDL cholesterol 2.0 mmol/litre or less, or non-HDL cholesterol 2.6 mmol/litre or less, with a full lipid profile on admission and at 2 to 3 months.4,19
  • Cardiac rehabilitation begins before discharge, with the first session within 10 days. Adjust doses for renal or hepatic impairment and check interactions in the BNF.3

Exam traps

  • The 120 minutes is not measured from arrival or from first medical contact. It runs from the moment fibrinolysis could otherwise have been given.
  • Tenecteplase is licensed within 6 hours of symptom onset, but the NICE fibrinolysis window is 12 hours. The licence and the guideline answer different questions.
  • Alteplase is dosed differently for myocardial infarction, pulmonary embolism and stroke. STEMI uses the accelerated myocardial infarction regimen; using another is the classic error.
  • The NICE ticagrelor recommendation is for STEMI not treated with PCI, a later branch. It is not the antiplatelet given at the moment of fibrinolysis.
  • Posterior infarction is an occluded artery and earns primary PCI. Do not call ST depression in V1 to V3 a non-ST-elevation myocardial infarction without posterior leads.
  • In right-ventricular infarction the circulation is preload dependent, so glyceryl trinitrate and other preload reducers can cause severe hypotension.
  • Enoxaparin after lysis has no IV loading bolus from age 75, and the subcutaneous dose is lower.
  • Prasugrel drops to 5 mg once daily under 60 kg or from 75 years, and clopidogrel loses its loading dose from 76 years.
  • Do not use level of consciousness after cardiac arrest caused by suspected STEMI to decide eligibility for angiography.
  • Suspected aortic dissection contraindicates fibrinolysis, so examine for it before the lytic, not after.
  • NICE NG185 contains no oxygen recommendation at all. The saturation targets come from CG95, and routine oxygen is not given.

Illustrations

Acute STEMI on 12-lead ECGTwelve-lead ECG showing regional ST-segment elevation with reciprocal ST depression. In a compatible acute ischaemic presentation this pattern supports a working diagnosis of STEMI and immediate reperfusion assessment, but the tracing must be interpreted in its clinical context.Displaced, Wikimedia Commons · Public domain

Key sources

  1. NICE, Recent-onset chest pain of suspected cardiac origin: assessment and diagnosis, full guideline text published by NICE on NCBI Bookshelf (CG95)Published 24 Mar 2010 | Updated 30 Nov 2016
  2. Thygesen K and others, Fourth Universal Definition of Myocardial Infarction (2018), Table 2 and sections 27, 28 and 32 (doi:10.1161/CIR.0000000000000617)Published 25 Aug 2018
  3. NICE, Acute coronary syndromes (NG185)Published 18 Nov 2020
  4. NICE, Cardiovascular disease: risk assessment and reduction, including lipid modification (NG238)Published 14 Dec 2023
  5. Resuscitation Council UK, The ABCDE approachPublished 1 Oct 2015 | Updated 1 Jul 2024
  6. BNF, Aspirin (BNF drug monograph)
  7. BNF, Glyceryl trinitrate (BNF drug monograph)
  8. BNF, Morphine (BNF drug monograph)
  9. BNF, Prasugrel (BNF drug monograph)
  10. BNF, Clopidogrel (BNF drug monograph)
  11. BNF, Tenecteplase (BNF drug monograph)
  12. BNF, Alteplase (BNF drug monograph)
  13. BNF, Enoxaparin sodium (BNF drug monograph)
  14. BNF, Fondaparinux sodium (BNF drug monograph)
  15. Clopidogrel 75 mg film-coated tablets, Summary of Product Characteristics, section 4.2 Posology (emc product 10634)Published 12 Dec 2023 | Updated 8 Jan 2024
  16. BNF, Ticagrelor (BNF drug monograph)
  17. BNF, Ramipril (BNF drug monograph)
  18. BNF, Bisoprolol fumarate (BNF drug monograph)
  19. BNF, Atorvastatin (BNF drug monograph)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.