PROGRESS IN THE DEVELOPMENT OF A TRILEAFLET MECHANICAL HEART VALVE (MHV)
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Progress continues in the development of a trileaflet MHV (Triflo Medical, Inc., Costa Mesa, CA) that does not necessitate anticoagulation therapy. Three versions have been studied in calves: a prototype with delrin leaflets, a similar model, the T1 with pyrolytic carbon leaflets and reduced swing angle from 60 to 50 and the final version, the T2. The T2 was redesigned using flow visualization and computational fluid dynamic (CFD) analysis, in an effort to optimize the valve's hemodynamic characteristics, minimize thrombogenicity and duplicate physiologic valve closing characteristics. All versions have undergone extensive in vitro testing at the Helmholtz Institute, Aachen, Germany. A brief review of design changes and in vitro testing is presented along with the results of ongoing in vivo studies testing versions T1 and T2. In a recently completed study, 14 calves (80 to 100kgs) each received a 29mm T1 valve in the mitral position. Five experiments were ended early because of surgical complications. The intended study duration was 3 months, but 1 experiment was continued for 502 days to investigate the feasibility of in vivo leaflet wear testing. In an ongoing study involving the same calf model, seven model T2 MHVs are being tested in experiments designed to last 5 to 6 months. Four of these experiments have been completed, 1 of which was terminated at 104 days because of infection. The other 3 are ongoing. In all full-term studies, valve performance was excellent, as evidenced by satisfactory intraoperative echocardiography findings, normal weight gain, activity and good health. In each case, I.V. heparin therapy (100mg/day) was discontinued after 10 days. Hematologically, the full-term calves remained within normal limits. At the end of the experiments, left heart catherization showed a mean transvalvular pressure gradient of 10.522.21 mmHg and insignificant valvular regurgitation at heart rates from 50 to 190 bpm and cardiac outputs from 4 to 20 L/min. Gross examination of explanted valves showed no thrombus deposits. Histopathologic examination of major organs showed no evidence of thromboembolic events. Both the T1 and T2 valves performed well without long-term anticoagulation in the calf MVR model.
