Development of an Orthotopic Pulmonary Valve Replacement Porcine Model for Mechanical Heart Valve Thrombosis

Objective Animal models are indispensable for the development of valve prostheses like we currently know them. Recent developments have questioned the validity of sheep as the model of choice for the evaluation of mechanical heart valves. The pig has been raised as a better alternative due to a more comparable coagulation system. We therefore compared the thrombogenicity of the sheep compared to the pig in a model of pulmonary valve replacement. Methods Pigs (n = 12) and sheep (n = 5) underwent pulmonary valve replacement with a mechanical valve in orthotopic position. No antithrombotic medication of any kind was given. Follow-up period was 5 months or until established valve thrombosis. Valve performance was assessed by monthly cardiac ultrasounds combined with post-mortem macro- and microscopical analysis of the valve and downstream organs. Results In the pig cohort, valve thrombosis was established after less than a month in all but one animal. Post-mortem valve examination showed terminal valve thrombosis with immobilized hinges. In the sheep cohort, all animals completed the follow-up period of 5 months. At post-mortem examination, all valves were free from any thrombi or deposits with both leaflets mobile. Conclusion The sheep model appears not thrombogenic enough to elicit mechanical valve thrombosis in the highly thrombogenic pulmonary position. Contrarily, the porcine model elicits massive thrombosis at a fast rate in an identical position. These findings confirm that we should shift to the pig as a standard for (mechanical valve) thrombosis research.