Right coronary artery occlusion
- ST depression in lead I
- ST elevation in lead III greater than in lead II
a. Proximal occlusion
- ST elevation more than 1 mm with positive T wave in lead V₄R
b. Distal occlusion
- ST isoelectric with a positive T wave in lead V₄R
Left circumflex artery occlusion
- ST elevation in lead II greater than lead III
- ST isoelectric or elevated in lead I
- ST isoelectric or depressed with negative T wave in V₄R
a. Extension to posterior wall
- ST depression in precordial leads
b. Extension to lateral wall
- ST elevation in leads I, aVL, V₅, and V₆
Left anterior descending artery occlusion
a. Proximal to first septal branch and first diagonal branch
- ST elevation in leads aVR and aVL
- ST depression in leads II, III, and aVF
- ST elevation in lead V₁ (> 2 mm) and leads V₂ to V₄
- ST isoelectric or depressed in leads V₅ and V₆
- Acquired intra-Hisian or RBBB may occur
b. Distal to first septal branch, proximal to first diagonal branch
- ST elevation in lead I and aVL
- ST depression in lead III (lead II is isoelectric)
- ST elevation in leads V₂ to V₆ but not in lead V₁
c. Distal to first diagonal branch, proximal to first septal branch
- ST depression in lead aVL, highest in lead III
- ST elevation in inferior leads, highest in lead III
- ST elevation in leads V₁ to V₄
d. Distal LAD
- ST depression in aVR
- ST elevation in inferior leads, highest in lead II
- ST elevation in leads V₃ to V₆
Left main coronary artery occlusion
- ST elevation in lead aVR
- ST elevation in lead V₁ (lower than that of lead aVR)
- ST depression in leads II and aVF
- ST depression in the precordial leads to the left of V₂

ECG STEMI / MI Patterns: Acute Anterolateral MI

ST ↑ in I, aVL, V3–V6. Poor R wave progression. T wave inversion. Usually LAD occlusion ± RCA/LCx involvement.

Acute Inferior & Posterior MI

ST ↑ in II, III, aVF. Q waves, T inversion. Posterior MI shows ST ↓ in V1–V2 with tall R in V1. Most often due to RCA occlusion.

Acute Right Ventricular MI

ST ↑ in aVR (± V1). Often accompanies inferior MI. Due to proximal RCA occlusion. Can cause hypotension with nitrates.

Acute Septal MI

ST ↑ in V2–V3. Q waves, T inversion. Due to LAD septal branch occlusion.

Anterior STEMI with Tombstoning

Old Inferior MI

Q waves in II, III, aVF. T inversion/flattening. No acute ST changes.

Old Anterolateral MI

Q waves in I, aVL, V2–6. Loss of R waves in V2–5. T inversion V5–V6.

Acute Inferolateral MI

ST ↑ in I, II, aVL, aVF, V3–6. Pathological Q in aVL.

Acute Inf + True Posterior MI

Inferior ST ↑ (II, III, aVF). Posterior changes: ST ↓ V1–V2, tall R in V1.

⚠️ Emergency note: ST elevation + chest pain = treat as STEMI. Activate reperfusion pathway (PCI or thrombolysis) immediately.

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ECG - STEMI

Site of Coronary Artery Occlusion in STEMI