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Posterior STEMI

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Posterior myocardial infarction involves the posterior wall of the left ventricle, usually from occlusion of the right coronary or left circumflex artery. On the standard ECG it appears as mirror-image changes in V1-V3, and true ST elevation is seen only on posterior leads V7-V9.

ECG criteria

  • Horizontal ST depression in V1-V3 (the mirror image of posterior ST elevation).
  • Tall, broad R waves in V1-V2 (R/S ratio above 1), the mirror of posterior Q waves.
  • Upright, prominent T waves in V1-V3 (mirror of T-wave inversion).
  • ST elevation of 0.5 mm or more in posterior leads V7-V9 confirms the diagnosis.
  • Frequently accompanies inferior or lateral STEMI; posterior ST elevation is considered an STEMI equivalent.

Mechanism

Occlusion of the artery supplying the posterior wall, usually the posterior descending branch of the right coronary artery or a posterolateral branch of the circumflex, causes posterior injury. The standard anterior leads face this wall from the opposite side, so they record the reciprocal image of the injury.

Common causes

  • Atherosclerotic plaque rupture with thrombosis in the right coronary or left circumflex artery.
  • Usually extends from an inferior or lateral infarction; isolated posterior infarction is less common.
  • Risk factors: smoking, diabetes, hypertension, dyslipidaemia, family history.

Management principles

Posterior STEMI is managed as an STEMI equivalent with rapid reperfusion within the local STEMI pathway. Recognition depends on suspicion and on recording posterior leads V7-V9; follow local guidelines.

High-level principles for study. Treatment decisions follow local guidelines and the clinical situation.

Pitfalls and mimics

  • ST depression in V1-V3 is easily mistaken for anterior subendocardial ischaemia; the upright T waves and tall R waves point to a posterior infarct, confirmed with V7-V9.
  • Tall R waves in V1 also occur in right bundle branch block, right ventricular hypertrophy and Wolff-Parkinson-White pre-excitation; clinical context and posterior leads distinguish them.
  • Missing the diagnosis delays reperfusion, because no ST elevation appears on the standard 12 leads.

Practise in the ECG trainer — Recognise this pattern on generated tracings.

References

  1. 2023 ESC Guidelines for the management of acute coronary syndromes. European Society of Cardiology (2023) — Tier 2 (guidelines / primary literature)
  2. Fourth Universal Definition of Myocardial Infarction (2018). ESC / ACC / AHA / World Heart Federation (2018) — Tier 2 (guidelines / primary literature)
  3. Wagner GS, Strauss DG. Marriott's Practical Electrocardiography. Wolters Kluwer, 12th edition (2013) — Tier 3 (textbook)

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