Stability of an artificially seeded endothelial cell layer on aortic bioprostheses in a heterotopic sheep model

Abstract

Introduction: The stability of an endothelial cell (EC) layer established on stentless aortic bioprostheses was evaluated under in-vivo conditions in a sheep model. Methods: EC and fibroblasts were harvested from the external jugular vein of seven sheep. After fluorescence labelling (PKH-26), the cells were seeded onto pretreated (citric acid) stentless aortic valves (Freestyle, Medtronic). Three unseeded prostheses served as controls. The valves were implanted into the descending aorta. Using an aorto-left atrial shunt, systolic/diastolic movements of the leaflets were achieved and documented by direct intraoperative sonography. Postoperatively, the animals received no anticoagulative therapy. After three months, the chests were reopened and the valves were explanted. Specimen for immunohistochemical staining and scanning electron microscopy (SEM) were taken prior to implantation and after explantation. Results: All animals survived surgery. One animal of the study group died on the first postoperative day. A still confluent EC layer of labelled cells covered the the surface of this valve. The other valves were explanted after three months. Control group: Neointimal covering of the first 0.5cm of the prostheses. Structural degeneration with evident leaflet retraction and thrombus formation was found in all sinuses. No EC layer was seen on the cusps. Study group: Degeneration was similar. In contrast, leaflets and sinuses were covered with EC as was proven with immunohistochemical stainings and by SEM. No thrombus was found in the sinuses of these valves. The EC layer established on stentless biological valves remained stable and seemed to suppress thrombus formation thus increasing biocompatibility.