South African Flag Sign in Acute Myocardial Infarction: A Case Report and Literature Review Highlighting the Superiority of the Occlusion Myocardial Infarction (OMI)/Non-Occlusion Myocardial Infarction (NOMI) Paradigm

The South African flag sign (SAFS) is a recently described electrocardiographic (ECG) pattern characterized by ST-segment elevation in leads I, aVL, and V2, with reciprocal ST-segment depression in lead III. It represents a subtle but specific marker of acute occlusion of the first diagonal (D1) branch of the left anterior descending (LAD) artery and is considered a ST-elevation myocardial infarction (STEMI)-equivalent pattern within the occlusion myocardial infarction (OMI) paradigm. We report the case of a 69-year-old male who presented with chest pain and fatigue. Initial ECG demonstrated normal sinus rhythm with deep Q waves in leads I and aVL, minimal ST-segment depression in the inferior leads, and subtle ST-segment elevation in leads I, aVL, and V2 - findings retrospectively consistent with the SAFS. Cardiac biomarkers were markedly elevated, and echocardiography revealed anterolateral wall hypokinesis with preserved left ventricular systolic function. Coronary angiography identified a 100% thrombotic occlusion of the D1 artery and a 90% complex stenotic lesion extending from the proximal to mid-LAD. Percutaneous coronary intervention (PCI) with drug-eluting stent placement was successfully performed in both lesions, restoring flow. The patient was discharged on dual antiplatelet therapy and high-intensity statin. This case highlights the importance of detailed ECG interpretation for early recognition of STEMI-equivalent patterns such as the SAFS, a subtle but reliable indicator of acute diagonal artery occlusion, and underscores the clinical relevance of the OMI/non-occlusion myocardial infarction (NOMI) paradigm, which more accurately identifies acute vessel occlusion than the traditional STEMI/non-ST-elevation myocardial infarction (NSTEMI) framework.