Serial angioscopic evidence of incomplete neointimal coverage after sirolimus-eluting stent implantation

Background - The time course of neointimal formation after stent implantation has not been studied extensively by angioscopy in the drug-eluting stent era. Methods and Results - Serial angioscopic findings at first follow-up (3.6 +/- 1.1 months), second follow-up (10.5 +/- 1.6 months), and third follow-up (21.2 +/- 2.2 months) after stent implantation were compared between sirolimus-eluting stents (SES, n=17) and bare-metal stents (BMS, n=11). Neointimal coverage, thrombus, and presence of yellow plaques underneath the stents were assessed. Neointimal coverage was graded as follows: grade 0, stent struts were fully visible; grade 1, struts bulged into the lumen, although they were covered; grade 2, struts were embedded by the neointima but were seen translucently; or grade 3, struts were fully embedded and invisible. Neointimal coverage was remarkably different between SES and BMS at each follow-up point. Neointimal coverage grade was 1.1 +/- 0.5 in SES versus 2.9 +/- 0.3 in BMS at the first follow-up (P < 0.0001), 1.1 +/- 0.5 in SES versus 3.0 +/- 0.0 in BMS (P < 0.0001) at the second follow-up, and 1.3 +/- 0.5 in SES versus 3.0 +/- 0.0 in BMS at the third follow-up (P=0.0009). No significant serial changes in coverage grade were noted in the BMS group, whereas coverage grade slightly but significantly increased at the third follow-up in the SES group (P < 0.05). Thrombi were detected in 4 SES: a red thrombus was seen from the first to the third follow-up in 2; another was detected only at the third follow-up; and the fourth was seen at the first follow-up but disappeared at the second follow-up, associated with a new white thrombus despite dual antiplatelet therapy. Yellow plaques had disappeared by the time of the second follow-up in BMS. In contrast, yellow plaques were exposed in 71% of SES at the first follow-up and remained exposed until the third follow-up. Neointimal coverage grades correlated with thrombi (P=0.002) and with yellow plaques (P < 0.0001). Conclusions - Serial angioscopic findings up to 2 years after SES implantation were markedly different from those after BMS. Neointimal coverage was completed by 3 to 6 months in BMS. In contrast, SES demonstrated the presence of thrombi and yellow plaques even as much as 2 years after implantation.