Occlusion of the circumflex or a dominant right coronary artery can infarct the posterior wall without ST elevation on the standard 12-lead ECG. The reciprocal sign is horizontal ST depression in V1 to V3, often with tall R waves and upright T waves.
When you see it in a patient with ischaemic symptoms, record posterior leads V7 to V9: ST elevation of 0.5 mm or more there confirms posterior infarction. Treat it as an occlusion and discuss immediate reperfusion with cardiology.
- Look for horizontal ST depression in V1–V3 in any patient with chest pain
- Record V7–V9 when you see it; 0.5 mm elevation confirms posterior infarction
- Repeat the ECG every 15–30 minutes if symptoms continue and the first is non-diagnostic
- Escalate for immediate angiography when posterior occlusion is suspected
Why it matters
It is one of the commonest coronary occlusions that a STEMI-only rule misses.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for emergency & critical care, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free