Acute Left Main Coronary Artery Occlusion with South African Flag Sign on Electrocardiogram: A Case Report

Background: The South African flag sign(SAFS) in electrocardiogram(ECG) indicates that the patient may have acute high lateral wall myocardial infarction typically linked to first diagonal branch occlusion, which has not been reported in Left Main Coronary Artery(LMCA) occlusion. Case Presentation: A 69-year-old female with primary hypertension presenting with chest pain for 1.5 hours. Initial ECG findings indicated SAFS, suggesting a high lateral myocardial infarction initially believed to involve the first diagonal branch. However, emergent coronary angiography revealed an unexpected complete occlusion of the LMCA with no collateral flow (thrombolysis in myocardial infarction [TIMI] flow grade 0). The patient underwent successful percutaneous coronary intervention, which restored optimal blood flow (TIMI grade III). The patient was managed with a comprehensive medication regimen, leading to an uneventful recovery and discharge without complications. Follow-up assessments at one and six months showed no adverse cardiac events or symptoms. Conclusions: This case underscores the need for heightened clinical vigilance when interpreting ECG with SAFS, as it may indicate more severe coronary artery pathology. The report also suggests a reevaluation of the diagnostic utility of SAFS in identifying the site and severity of coronary artery occlusions.