In-vitro localization of initial flow-induced thrombus formation in bileaflet mechanical heart valves

A major concern with mechanical heart valve prostheses is still the need for lifelong anticoagulation to prevent valve thrombosis and thrombembolism. Knowledge of the localization of initial thrombus formation on the prosthesis may help to improve valve design. Since observation of early clot deposition in vivo is difficult, the aim of this study was a detailed assessment of the initial stages of thrombus formation at bileaflet mechanical heart valves by means of an in-vitro clotting model. Four different bileaflet mechanical heart valves (St. Jude Medical, CarboMedics, ATS and On-X) were investigated in a mock circulation in aortic position using enzyme-activated milk resembling blood clotting potential. Initial development of clot formation on the valves was documented photographically and frequency of occurrence was analyzed for both location and valve type. For the bileaflet valves, clot depositions could be found in a distinct pattern similar in all types. In initial stages, clots developed downstream of the leaflets near the orifice ring, 61.5+/-5.8% of which were hinge associated, but 38.5+/-5.8% were located isolated laterally and medially remote of the hinge region, providing new information on thrombus formation potentially useful for improvement of valve design.