Histopathology of Clinical Coronary Restenosis in Drug-Eluting Versus Bare Metal Stents

To characterize in-stent restenosis after the implantation of sirolimus-eluting stents (SES), paclitaxel-eluting stents (PES), tacrolimus-eluting stents (TES), and zotarolimus-eluting stents (ZES), 25 patients treated with drug-eluting stents (DES; 9 PES, 10 SES, 4 TES, and 2 ZES) and 19 with bare-metal stents (BMS) underwent directional coronary atherectomy for in-stent restenosis 4 to 36 months after implantation. Restenosis after DES implantation was more frequently focal and associated with smaller specimens compared to that after BMS implantation. Light and confocal microscopy were used. Histologic features were similar in DES and BMS. In-stent restenotic lesions were composed mainly of neointima containing proteoglycan-rich smooth muscle cells and fibrolipidic regions. Small inflammatory infiltrates were observed, mostly in patients with unstable angina; CD18- and/or CD3⁺ cells were detected in patients with BMS and DES. Different smooth muscle cell phenotypes were observed: synthetic was more frequent with BMS and PES, intermediate with ZES, contractile or intermediate with SES, and contractile with TES. The mean proliferation index was low and comparable among stent types; cyclins B1 and D1 were expressed in all DES. In conclusion, intra-DES and intra-BMS restenotic tissue was composed mainly of smooth muscle cells with different phenotypes, proliferating at a low rate. The different smooth muscle cell phenotypes within the stent types might suggest different mechanisms of restenosis.