Middle-aged patient presenting with chest pain. Describe the ECG.


Describe and interpret this ECG


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).

Signs of occlusion proximal to S1

Signs of basal septal involvement:

  • New RBBB — occurs due to septal infarction
  • ST elevation in V1 > 2.5 mm
  • ST elevation in aVR 
  • ST depression in V5
Signs of occlusion proximal to D1

Signs of high lateral involvement:

  • ST elevation in aVL
  • Inferior reciprocal ST depression > 1 mm 

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


TOP 100 ECG Series

Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Adult/Paediatric Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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