Septal Myocarditis Mimicking Proximal Left Anterior Descending Artery Occlusion.

BACKGROUND: Acute myocarditis is a recognized ST-segment elevation myocardial infarction mimic; however, focal septal myocarditis presenting with a proximal left anterior descending artery infarction phenotype is uncommon. CASE SUMMARY: A previously well 21-year-old woman presented with acute chest pain, marked high-sensitivity troponin elevation, anteroseptal ST-segment elevation, accelerated junctional rhythm, and bifascicular block. Coronary angiography demonstrated nonobstructive coronary arteries. Cardiac magnetic resonance (CMR) showed focal septal edema with nonischemic late gadolinium enhancement consistent with acute myocarditis, accompanied by transient biventricular systolic dysfunction, confirming acute myocarditis. She recovered with guideline-directed medical therapy. DISCUSSION: Focal septal myocarditis should be considered after exclusion of obstructive coronary disease in patients with a convincing ST-segment elevation myocardial infarction phenotype. Early CMR is pivotal for establishing the diagnosis and guiding management. TAKE-HOME MESSAGES: Focal septal myocarditis may closely mimic proximal left anterior descending artery occlusion. Cardiac magnetic resonance is essential for diagnosis after normal coronary angiography.