Study of Vascular Healing With the Combo Stent Versus the Everolimus Eluting Stent in ACS Patients by Means of OCT

BACKGROUND The implantation of bare-metal stents (BMS) has significantly reduced clinical and angiographic restenosis compared to balloon angioplasty alone after PCI due to eliminating elastic recoil and reducing arterial remodeling. However, in-stent restenosis still occurred frequently after BMS implantation in 20% to 40% of patients due to neointimal proliferation. The development, clinical validation and widespread use of drug-eluting stents (DES) have revolutionized the treatment of patients with coronary artery disease. Large-scale, prospective, multicenter double-blind randomized trials have provided strong evidence that drug-eluting stents significantly reduce angiographic restenosis and enhance event-free survival compared with BMS after implantation in native coronary arteries (3-6).However, despite an improved efficacy in the prevention of restenosis and target vessel failure safety concerns have been raised for DES, focusing on a small but clinically important increase in stent thrombosis occurring greater than one year after the index procedure.

In patients receiving drug-eluting stents, the acute coronary syndrome has been identified as one of the major risk factors of stent thrombosis (10). Therefore, concerns about the long-term outcome and safety after drug-eluting stent implantation due to late stent thrombosis and late stent malapposition have been raised.

Stent thrombosis, in particular late stent thrombosis, has been related to an impaired stent healing, most of all to a reduced endothelial repair, i.e. reduced stent strut coverage, after implantation of drug-eluting stents. This has resulted in the recommendation of a prolonged 12-month double antiplatelet therapy with aspirin and clopidogrel after drug-eluting stent implantation, however, how long double antiplatelet therapy is needed is unknown at present. These observations have resulted in an intense search for alternative strategies to promote stent healing and endothelial repair, rather than to inhibit the endothelialisation of the stent, that is common to the substances used to prevent neointima formation.

Notably, endothelial repair can be substantially stimulated by CD34+ endothelial progenitor cells. The Combo stent is therefore covered with a CD34+ antibody to attract endothelial progenitor cells to promote endothelial and stent healing, and on the abluminal side releases sirolimus to prevent neointima formation and restenosis. Several preclinical studies in the porcine coronary artery model have shown, that endothelialisation and stent healing are accelerated in the Combo stent. The present study has therefore been designed to compare stent healing of the Combo stent with the everolimus-eluting stent by optical coherence tomography analysis (optical frequency domain imaging; OFDI), a high resolution intracoronary imaging technique allowing accurate evaluation of stent coverage and healing, in patients with an acute coronary syndrome. Previous studies have indicated, that coronary stent healing after DES implantation is particularly impaired in patients with ACS, and therefore this patient population is in a particular need of improved "pro-healing" stent concepts with a high efficacy.

RATIONALE An important limitation of stents eluting only growth-inhibiting substances is, that also the desirable endothelial cell growth over the stent struts is prevented, that is thought to represent a major cause of "late-stent-thrombosis". The rationale for the design of the "combo-stent" is therefore to combine a growth inhibiting substance with abluminal release with an endothelial progenitor cell attracting design to promote endothelial repair. In the pre-clinical studies, the "Combo Stent" demonstrated significantly lower neointimal hyperplasia, while also showing improved endothelial coverage relative to other commercially available DES. There was also a noticeably lower presence of inflammation and foreign body reaction.

OCT- Examination of Vessel Healing Optical coherence tomography (OCT) is a novel intravascular imaging modality based on infrared light emission that has a 10-20 fold higher resolution (10-20 µM) as compared to current intravascular ultrasound systems, and allows a detailed examination of stent healing. Strut coverage, strut apposition and neointima can be quantified at a micron-scale level with a resolution 10-20 times higher than conventional intravascular ultrasound. The quantification of stent healing by intravascular OCT analysis has recently been validated against histology, demonstrating an excellent accuracy of the OCT examination. Moreover, the safety and feasibility of OCT examination in a multicenter study has been demonstrated. Newer modalities of OCT image acquisition, as used in this study, have been reported to further simplify the technique and reduce procedural time.