Very Late Pathological Responses to Cobalt–Chromium Everolimus‐Eluting, Stainless Steel Sirolimus‐Eluting, and Cobalt–Chromium Bare Metal Stents in Humans

BACKGROUND The "very late" clinical outcomes for durable polymer drug-eluting stents and bare metal stents (BMSs) have been shown to be dissimilar in clinical studies. Conceptually, the long-term vascular compatibility of BMSs is still regarded to be superior to drug-eluting stents; however, no pathologic study to date has specifically addressed this issue. We evaluated the very late (≥1 year) pathologic responses to durable polymer drug-eluting stents (cobalt-chromium [CoCr] everolimus-eluting stents [EESs] and stainless steel sirolimus-eluting stents [SS-SESs]) versus BMSs (CoCr-BMSs). METHODS AND RESULTS From the CVPath stent registry, we studied a total of 119 lesions (40 CoCr-EESs, 44 SS-SESs, 35 CoCr-BMSs) from 92 autopsy cases with a duration ranging from 1 to 5 years. Sections of stented coronary segments were pathologically analyzed. Inflammation score and the percentage of struts with giant cells were lowest in CoCr-EESs (median inflammation score: 0.6; median percentage of struts with giant cells: 3.8%) followed by CoCr-BMSs (median inflammation score: 1.3 [P<0.01]; median percentage of struts with giant cells: 8.9% [P=0.02]) and SS-SESs (median inflammation score: 1.7 [P<0.01]; median percentage of struts with giant cells: 15.3% [P<0.01]). Polymer delamination was observed exclusively in SS-SESs and was associated with increased inflammatory and giant cell reactions. The prevalence of neoatherosclerosis with CoCr-EESs (50%) was significantly less than with SS-SESs (77%, P=0.02) but significantly greater than with CoCr-BMSs (20%, P<0.01). CONCLUSIONS CoCr-EESs, SS-SESs, and BMSs each demonstrated distinct vascular responses. CoCr-EESs demonstrated the least inflammation, near-equivalent healing to BMSs, and lower neointimal formation. These results challenge the belief that BMSs have superior biocompatibility compared with some polymeric coated drug-eluting stents and may have implications for future stent design.