ECG Case 034

Main Abnormalities

The ECG changes are partially masked by the presence of a right bundle branch block, but there is clear evidence of anteroseptal STEMI:

• Gross ST elevation in V1-3 (~ 5mm in V2)
• Convex ST elevation in I and aVL
• Reciprocal ST depression and T wave inversion in the inferior leads (II, III, aVF)

Predicting the Site of LAD Occlusion

This ECG demonstrates some markers of a very proximal LAD occlusion, involving the two most proximal branches of the LAD — the first septal branch (S1) and the first diagonal branch (D1).

This patient arrived by ambulance following an out-of-hospital VF arrest and was taken straight to the cath lab where he was found to have a complete ostial occlusion of his LAD.

A Common Pitfall 

This STEMI pattern is occasionally missed, when clinicians erroneously attribute the ST segment changes in V1-3 to RBBB alone.

However, the two patterns are quite different:

• Typical RBBB will have discordant ST depression and TWI in V1-3
• Superimposed septal STEMI will lead to ST elevation, Q wave formation, loss of the initial R wave and inversion of only the terminal portion of the T wave

Typical RBBB

RBBB + STEMI