- ST elevation in the inferior leads (II, III, aVF)
- ST elevation in the lateral leads (I, V5, V6)
Evidence of posterior STEMI
- Horizontal ST depression in V1-4 (maximal in V2-3)
- Dominant R wave in V2 (R/S ratio > 1)
- Upright T wave in V2
This pattern of infero-postero-lateral STEMI is most likely caused by occlusion of a dominant left circumflex artery.
Tips for spotting posterior infarction
Look specifically at lead V2 for the combination of
- Horizontal ST depression.
- Tall, broad R wave (>30ms wide, R/S ratio > 1) — this is a Q-wave equivalent.
- Upright T wave — particularly the terminal portion of the T wave.
One common trick is to turn the ECG over, hold it up to the light and look through it from behind. This inverts lead V2, which then takes on the appearance of a classic STEMI.
Sometimes it can be difficult to determine whether ST depression in V2-3 is due to posterior STEMI or simply subendocardial ischaemia affecting the anteroseptal wall. The diagnosis can be confirmed by recording posterior leads V7-9.
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