Differential Surface Thrombogenicity of Heparin Coated Bovine Pericardium: Implication in Bioprosthetic Valve Fabrication

Abstract

Sub-acute valve thrombosis limits the full potential of bovine pericardial valves. In this study, the effect of heparin coating and the influence of rough versus smooth pericardial surface on thrombogenicity was evaluated by in vitro methods. This was followed by mitral implantation of bioprosthetic valves with different inflow surfaces in sheep. The presence of conjugated heparin was demonstrated through O-toluidine blue staining and micro Raman spectroscopy. Heparin was estimated by a colorimetric assay for depletion of O-toluidine blue stain following exposure to heparin modified tissue. Functionality of surface bound heparin was demonstrated by platelet adhesion and protein adsorption studies. Difference in surface thrombogenicity of heparin coated rough and smooth surface was evaluated by modified whole blood kinetic clotting time method. Bioprosthetic valves with either rough or smooth surface of heparin coated pericardium forming the inflow surface were implanted in the mitral position of sheep and observed for device thrombosis upto 6 months. Heparin coating rendered the pericardial surface hydrophilic. Adsorbed protein on heparin coated pericardium was less compared to non-coated one. SEM images for platelet adhesion showed absence of platelets on heparin-coated tissue. Surface thrombogenicity evaluation showed difference in thromboresistance for heparin coated and uncoated pericardial surfaces and between heparin coated rough/smooth surfaces. Sheep implanted with valve having heparin coated rough surface
as valve inflow thrombosed in 53 days. In comparison, the valve having heparin coated smooth surface of pericardium forming the valve inflow surface completed the observation period of 6 and 12 months without any valve thrombosis.