ECG Case 014

Evidence of inferolateral STEMI:

• ST elevation in the inferior leads (II, III, aVF)
• ST elevation in the lateral leads (I, V5, V6)

Evidence of concurrent 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.

Look for evidence of posterior involvement in any patient with an inferior or lateral 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. However, poor transmission of current through aerated lung means ST elevation in posterior leads is not always evident, and normal posterior leads do not exclude posterior infarction.