Chronic thrombus occlusion after bare metal stenting in a patient with acute coronary syndrome visualized by optical coherence tomography.

We present a case of chronic thrombus occlusion visualized by optical coherence tomography (OCT) in a patient following bare metal stent (BMS) implantation. A 74-year-old Japanese man was treated with single BMS implantation for acute coronary syndrome. The second follow-up angiography demonstrated no restenosis at the BMS site in the convalescent phase before discharge. A third coronary angiography at 6 months after BMS implantation showed sub-total occlusion at a site just proximal to the BMS. OCT was performed to evaluate in-stent restenosis. OCT demonstrated an organized thrombus-like image containing a micro-channel in the target lesion. Repeat percutaneous coronary intervention (PCI) was performed with a distal protection device and we were able to aspirate some tissue from the culprit lesion. Pathological examination of this tissue revealed an organized fibrin thrombus with angiogenesis. Phosphotungstic acid hematoxylin staining and CD68 immunological staining were positive in this tissue. Moreover, immunological staining for CD34 was positive in the micro-channel of this tissue, suggesting chronic build up. This case demonstrated that chronic, organized thrombus formation is a possible cause of restenosis after BMS implantation in the convalescent phase, and that OCT is a useful modality to discriminate thrombus formation from regular neo-intimal hyperplasia in in-stent restenosis lesions.