Asian Journal of Cardiology Research

Background: Determining the infarct-related artery (IRA) in inferior ST-elevation myocardial infarction (STEMI) is generally guided by electrocardiographic (ECG) and angiographic characteristics. Diagnostic uncertainty increases when both the right coronary artery (RCA) and left circumflex artery (LCx) are diseased or occluded, particularly in the presence of chronic total occlusion or heavy calcification.

Case Presentations: We describe two patients presenting with infero-basal STEMI and severe multivessel coronary artery disease. In the first case, dual occlusion of the RCA and LCx            occurred in a patient with prior in-stent LCx revascularisation. ECG and echocardiography yielded discordant territorial patterns, whereas angiography revealed diffuse calcification. Selective guidewire probing demonstrated that the RCA lesion was chronic, whereas the in-stent LCx occlusion was acute and thrombotic, restoring TIMI 3 flow. In the second case, an apparently thrombotic RCA occlusion with full collateralization co-existed with a severe proximal LCx stenosis. Progressive wire escalation confirmed chronic RCA occlusion and acute LCx occlusion, both successfully revascularized.

Discussion and Conclusion: These cases illustrate the limitations of isolated ECG or angiographic interpretation for culprit lesion identification in complex inferior STEMI. Contemporary evidence confirms that the RCA is the most frequent culprit artery, although LCx occlusion remains under-recognised. We integrate two complementary diagnostic strategies: an ECG-based algorithm derived from Fiol et al., and an angiography-guided algorithm incorporating selective wire probing when diagnostic ambiguity persists. Accurate IRA identification in infero-basal STEMI with dual occlusions requires a structured multimodal diagnostic approach.