Activate or Wait – 002

58-year-old male with left scapular pain and nausea. T2DM, 130kg.

We are 20 minutes from your tertiary centre.

Would you activate your cath lab/STEMI protocol?

ECG interpretation

High lateral STEMI

  • ST elevation and hyperacute T waves in lead I, aVL, V2
  • Reciprocal ST depression in II, III, aVF, V3-5
  • Occasional ventricular ectopics

This characteristic pattern of ST segment changes resembles the South Africa flag and is usually caused by occlusion of the first diagonal branch of the LAD (LAD-D1).

South Africa Flag sign:

High lateral STEMI South African Flag sign

There is no lead that directly reflects the “high lateral region” usually supplied by the LAD-D1 vessel. Infarction of this territory therefore often causes subtle ST segment changes that fail to meet STEMI criteria. Lead III is directly reciprocal to this region, and thus ST depression and T-wave inversion in lead III is often more pronounced than any ST elevation seen elsewhere (see both ECGs).

Left circumflex artery occlusion can also cause this ECG pattern, but usually produces associated ST elevation in leads V5-6.


Key finding:

LAD-D1 occlusion


  • Left Main Coronary Artery – Irregular
  • Left Anterior Descending Coronary Artery – 70% proximal stenosis, LAD-D1 complete occlusion
  • Left Circumflex Coronary Artery – Irregular
  • Right Coronary Artery – Dominant, irregular


  1. PCI to LAD-D1 and LAD
Clinical Pearls
  • The South Africa Flag Sign should be in every critical care practitioner’s knowledge base as a “STEMI-equivalent”, regardless of the magnitude of ST-segment changes seen. The apparent non-contiguous nature of ST elevation means this pattern can be overlooked even by experienced Emergency Physicians
  • Lead III is directly reciprocal to the high lateral region and thus may manifest the most pronounced ECG changes seen in high lateral OMI


Further reading

Online resources


EKG Interpretation

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

MBBS (Hons), BMSci (Hons). Cardiology Registrar at Royal Perth Hospital in Perth, Australia. Graduate of The University of Western Australia in 2016 with Honours and completed Basic Physician Training with the RACP in 2021. Passion lie in cardiac imaging and electrophysiology.

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