Optical Coherence TomOgraphy Assessment of the Drug-Eluting Stent

Overview

BACKGROUND Treatment of coronary atherosclerotic disease has been significantly advanced by interventional cardiology, and the advent of coronary arterial stents. In comparison to angioplasty alone, stents have reduced the incidence of angiographic as well as clinical restenosis, the recurrence of angina, the need for coronary arterial bypass graft (CABG) surgery, repeat revascularization and the occurrence of major adverse cardiac events (MACE).However the long-term success of this therapy has been limited by the occurrence of in-stent restenosis. Despite the effectiveness of intracoronary stents in maintaining a larger luminal diameter, as compared to angioplasty alone, in-stent restenosis occurs within 6 to 9 months after stent placement in 15% to 35% of patients. While stents can reduce restenosis by blocking vascular recoil and remodeling, mechanical intervention alone has been incapable of treating this biological problem of neointimal hyperplasia, particularly in the subset of patients with diabetes, long lesions or small vessel disease.Drug-eluting stents (DES) were developed as a viable method for focused delivery of anti-restenosis compounds to target lesions for the reduction of restenosis. Of the DES available and with the results of up to six (6) years clinical follow-up, the sirolimus-eluting stent (SES) has become the current gold standard for stent implantation. With the advent of using DES to treat complex lesions such as longer lesions requiring the use of multiple stents and the use in bifurcation lesions, the risk of stent thrombosis has increase.Late stent thrombosis has also been reported following DES implantation.Long term treatment with dual anti-platelet therapy following stent implantation has become the solution used to counteract the risk of stent thrombosis, this solution does not come without it's own risks and is an expensive therapy. Another specific problem of DES is delayed endothelization, and this may be and attributing factor in prolonging the period of thrombotic risk as shown by pathological findings at autopsy following SES implantation. These examinations have shown that even after 16 months, neointimal healing is still incomplete with approximately 20% of stent struts being found uncovered. Questions have arose that the problems of late thrombosis and delayed endothelization of stent struts with DES could be the result of the permanent polymer that is used as the bonding agent for the anti-restenosis compounds to the stents.Intravascular Ultrasound (IVUS) along with angiography has been the techniques used to gain data on DES to this point. Angiography is a 2 dimensional tool that gives a view of the vessel and IVUS gives a more 3 dimensional view of the vessel. IVUS does have its limitations, as stent struts are reflectors of sonic waves, shadowing around and behind the struts occurs. IVUS is also limited in detecting malapposition of the struts to the vessel wall especially if the area between the vessel wall and the strut in very small. RATIONALE Optical Coherence Tomography (OCT) is an optical analogue of IVUS that uses an infrared light source and measures the backscatter of the light. With this technique a higher level of resolution compared with IVUS has been reported.OCT has been reported as being able to visualize and detect atherosclerotic plaques and assess more accurately strut malapposition and the presence or thickness of neointimal hyperplasia as compared to IVUS. With the question of delayed endothelization due to the permanent polymer being a probable risk for late stent thrombosis, it is felt that OCT post stent implantation may give a more accurate assessment of stent strut endothelial coverage. This study is designed to compare the intimal hyperplasia following implantation of the Excel DES with a biodegradable polymer vs. the Cypher DES with a permanent polymer using OCT.