South African Flag Sign in Left Anterior Descending Artery Occlusion Revealing Multivessel Coronary Artery Disease

Early recognition of subtle or atypical electrocardiographic patterns of acute coronary occlusion remains a major challenge in contemporary practice. The "South African flag sign" (SAFS) is characterised by concomitant ST-segment elevation in leads I-aVL and in the non-contiguous lead V2, together with reciprocal ST-segment depression in lead III and often in the remaining inferior leads, resulting in a distinctive spatial distribution of injury currents in the 4x3 electrocardiogram format, reminiscent of the South African national flag. It represents a marker of mid-anterior/anterolateral transmural ischaemia due to acute occlusion of the first diagonal (D1) branch of the left anterior descending (LAD) coronary artery. However, this pattern is not currently incorporated into international guidelines and remains underrecognised in clinical practice. We report the case of an elderly woman presenting with acute coronary syndrome (ACS) and transient ST-segment elevation, in whom the electrocardiogram revealed the SAFS. Urgent coronary angiography demonstrated a subocclusive proximal LAD bifurcation lesion extending to D1, as well as a critical mid-segment stenosis of the right coronary artery, an additional finding not previously described in patients presenting with this electrocardiographic sign. In addition, an intermediate branch free of critical disease and a well-developed second diagonal branch were identified, the latter showing flow limitation secondary to the proximal LAD bifurcation stenosis. Both critical lesions were treated with percutaneous coronary intervention and stent implantation. Despite reperfusion, the patient developed moderate left ventricular dysfunction. Her subsequent clinical course was uneventful, and she was discharged 10 days later. This case underscores the diagnostic and clinical relevance of SAFS in the setting of ACS, including its persistence despite the absence of conventional ST-elevation myocardial infarction (STEMI) criteria, and highlights the need for increased awareness of this electrocardiographic manifestation.