Beyond STEMI criteria: The electrocardiographic "South African Flag Sign" revealing an isolated proximal ramus intermedius occlusion.

The South African Flag Sign (SAFS) is an emerging ECG marker of acute coronary occlusion and a potential STEMI-equivalent, though not yet included in guidelines. It features ST elevation in I-aVL and V2 with reciprocal depression in III (and often in additional inferior leads) usually associated with first diagonal branch (D1) occlusion. We report a 66-year-old man with chest pain and SAFS, found to have an isolated sub-occlusive proximal ramus intermedius lesion successfully treated with primary PCI. This case shows that SAFS reflects an occlusion myocardial infarction and serves as a marker of the ischaemic territory rather than a specific culprit vessel, being generated by arteries other than D1 when they share a similar course and perfusion territory. Greater awareness may prevent misclassification and expedite reperfusion therapy.