Identifying Inferior ST-Segment Elevation Myocardial Infarction in the Presence of Left Bundle Branch Block

BACKGROUND: Diagnosing acute ST-segment elevation myocardial infarction (STEMI) in patients with left bundle branch block (LBBB) is challenging because baseline repolarization abnormalities can mask ischemic changes, delaying recognition and worsening outcomes. CASE SUMMARY: An 81-year-old woman with hypertension, type 2 diabetes mellitus, and chronic kidney disease presented with acute chest discomfort and dyspnea. Electrocardiography demonstrated a preexisting LBBB with new inferior ST-segment elevation. Emergent coronary angiography performed revealed an occluded mid-right coronary artery. She underwent successful percutaneous coronary intervention with drug-eluting stent placement. DISCUSSION: Inferior STEMI with LBBB is uncommon but remains high risk. The traditional STEMI/non-STEMI paradigm misses many occlusive infarctions, prompting adoption of the Occlusion MI framework. Although the original Sgarbossa criteria are specific but insensitive, modified Sgarbossa criteria using proportional ST deviation improve sensitivity with preserved specificity. TAKE-HOME MESSAGE: In patients with LBBB, accurate identification of acute coronary occlusion requires integration of modified Sgarbossa criteria with clinical judgment, rather than relying on LBBB alone.