Acute Ramus Intermedius Occlusion Presenting as the South African Flag Sign on Electrocardiogram.

Occlusion of the ramus intermedius (RI) artery is an uncommon but clinically significant cause of acute coronary syndrome, often mimicking other coronary occlusions and complicating diagnosis. We report the case of a 65-year-old man presenting with progressive typical angina chest pain whose electrocardiogram (ECG) showed the "South African flag sign", a pattern typically attributed to the first diagonal branch (D1) or left circumflex artery (LCx) occlusion. Coronary angiography, however, revealed a total occlusion with grade V thrombus of the proximal RI rather than D1 or LCx, and the patient underwent successful primary percutaneous coronary intervention (PCI) of the RI and left anterior descending artery. This case underlines that occlusive myocardial infarction (OMI) patterns such as the "South African flag sign" are not exclusive to D1 or LCx involvement but may also result from RI occlusion, emphasizing the need for clinicians to recognize atypical OMI electrocardiographic patterns for accurate diagnosis and timely reperfusion therapy. In addition, the ST-segment elevation in V5-V6 can serve as a clue to differentiate RI occlusion from D1, since the RI is located more laterally compared to D1 and its occlusion would result in ST-segment elevation in the lateral leads such as V5-V6.