A 67-year-old male was admitted because of acute myocardial infarction (AMI). An emergent coronary angiography showed a total occlusion in the left anterior descending artery, and a stent was deployed. Moderate lesion stenosis was found in the right coronary artery (RCA). Fractional flow reserve indicated 0.96, and percutaneous coronary intervention was not performed. Six months later, the patient visited an emergency room due to AMI. Angiograms showed a patency of the previous stent and progressed stenosis with filling delay of the RCA. Protruding red thrombi and plaque disruption of thin-cap fibroatheroma (TCFA) were identified by optical coherence tomography. Mild to moderate lesions are physiologically benign but morphologically malignant in cases of TCFA.
<Learning objective: Severe stenosis is a malignant index of plaque vulnerability on the basis of physiological and morphological evaluation. However, mild to moderate lesions are physiologically benign but morphologically malignant in cases of thin-cap fibroatheroma. Although fractional flow reserve can estimate the extent of severe stenosis, one of the elements of vulnerable plaques, it cannot always predict future events related to morphologically vulnerable plaques>