A Case of a High Lateral Acute Myocardial Infarction Caused by Occlusion of a First Diagonal Branch With Subtle Electrocardiogram Changes and Negative Cardiac Biomarkers at Presentation.

A 61-year-old man presented to our hospital with chest pain that had begun 50 minutes earlier. On arrival, an electrocardiogram (ECG) showed no obvious ST-T change, and troponin T was negative. The next morning, 11 hours after having chest pain, a re-examined ECG showed no obvious ST-T changes compared to the initial ECG, except for T wave inversion in lead aVL, and troponin T became positive. At that time, acute myocardial infarction (AMI) was highly suspected, and an emergent coronary angiogram was performed. Occlusion of the first diagonal branch was revealed, and successful percutaneous coronary angioplasty was performed. The later clinical course was uneventful. We realized that it is important to compare an initial ECG with serial or prior ECGs to be aware of subtle ECG changes and to repeat cardiac biomarker measurements a few hours later, in order not to miss or delay the diagnosis of AMI, when it has not been ruled out.