Hyperdominant Left Circumflex Artery Challenging Conventional Paradigms and Current Guideline Recommendations: A Comprehensive Literature Review and Case Series

Despite its rarity in the general population, left dominant coronary circulation with a hyperdominant left circumflex artery (LCx) has been associated with a more severe risk for ischemic and coronary artery disease. The concealment of an isolated posterior myocardial infarction (IPMI) on a standard 12-lead ECG among these patients with distinctive coronary anatomy can be concerning, especially when clinicians become trapped within conventional guideline-based diagnostic criteria, a circumstance that may ultimately be linked to a poorer prognosis. We present two cases that posed unique diagnostic challenges in this specific anatomical context. Case 1: A 63-year-old man presented to the emergency department (ED) with typical anginal chest pain and severe fatigue. Although the patient was initially diagnosed with non-ST-elevation myocardial infarction (NSTEMI), eventually a catastrophic occlusion of the left posterior descending artery (PDA) in the setting of a hyperdominant LCx was seen during coronary angiography (CAG). Case 2: A 69-year-old man arrived at the ED with typical angina, described as pressure-like. Although the serial 12-lead ECGs were completely normal, given the clinical context, the patient underwent an immediate invasive strategy in < 2 h. CAG revealed complete occlusion of the ostio-proximal segment of the left PDA. In both cases, hyperdominant LCx anatomy created a diagnostic blind spot within the conventional STEMI/NSTEMI paradigm, because the infarct territory was insufficiently captured by standard ECG criteria and failed to trigger guideline-based use of posterior leads or adjunctive imaging, thereby obscuring the diagnosis of IPMI. These cases warn clinicians about the diagnostic complexity of IPMI in a hyperdominant LCx setting. In such cases, ECG findings can be ambiguous or even completely absent, and the clinical presentation may not meet current unclear guideline-based indications for adjunctive diagnostic assessment, leading to delayed recognition of high-risk ischemia, particularly IPMI.