ComparisiOn of Neointimal coVerage betwEen zotaRolimus Eluting Stent and Everolimus Eluting Stent Using Optical Coherence Tomography at 3 Months

Recent autopsy study showed the most important histological and morphometric predictors of stent thrombosis were endothelial coverage and the ratio of uncovered to total strut after drug eluting stent (DES) implantation. Although there have been some controversies, incomplete stent apposition might be possible cause of very late stent thrombosis after DES implantation. Therefore, theoretically dual antiplatelet therapy should be continued to prevent the stent thrombosis until complete reendothelialization. But, detection of endothelial coverage over stent is not possible with available intravascular devices in clinical practice. Among currently available intravascular devices, intravascular optical coherence tomography (OCT) could give a more clear identification for a thin layer of neointimal hyperplasia (NIH) and malapposition with high-resolution (10 -20 μm) compared to intravascular ultrasound (100-150 μm). Previous OCT studies showed the significant different pattern of neointimal coverage between baremetal stent (BMS) and DES. In our experience, there were also some differences in neointimal coverage among the DESs, especially in zotarolimus eluting stent (ZES). ZES have been known to be associated with significantly more neointimal coverage than SES at 8 months intravascular untrasound (IVUS). This finding might be related with strut thickness and drug elution property. In our data, 99.7 % of stent struts were covered with neointima in ZES, but 93.2 % in sirolimus eluting stent (SES) at 9 month follow-up OCT. This difference was more distinct in patients with acute myocardial infarction (99.3 % in ZES vs.79.9 % in SES).

Both everolimus eluting stent (EES) was recently introduced and ZES resolute also will be available in the near future in Korea. Previous phosphorylcholine polymer was replaced with new, proprietary polymer which can provide extended elution kinetics in ZES resolute. Therefore, efficacy to suppress the neointimal growth might be improved but, safety for neointimal coverage needs to be evaluated in human coronary artery. Both new DESs are cobalt chrominum stent with thin stent strut and reported similar efficacy for suppressing the neointima growth. Also, endothelial coverage over stent strut occurred earlier compared to previous DESs (SES or PES) in animal experiments. But, there has been no data for neointimal coverage and malapposition of ZES resolute and EES using OCT in human coronary artery.

Recent paper according to Kubo et al reported that serial OCT examinations demonstrated markedly different vascular response up to 9 months after SES implantation between unstable angina and stable angina patients. These findings implied that initial native vessel status, which covered with stent, might be important and related with neoinitmal coverage and malapposition. But, there is little data evaluated the relationship between initial lesion status and neointimal coverage or late malapposition with OCT.

Therefore, this study will 1) evaluate the neointimal coverage and malapposition at 3 month after ZES resolute and EES implantation and 2) compare them between ZES resolute and EES at 3 months after stent implantation.

2. STUDY OBJECTIVE This study is an prospective open labeled randomized study to compare the neointimal coverage of ZES resolute (Endeavor® resolute) and EES (Xience®) in 3 month after stent implantation by OCT.