Further experience in the use of ancrod (Arvin) to prevent thrombosis on prosthetic heart valves.

Intravenous administration of ancrod produces hypofibrinogenaemia, which may be prolonged by further doses. Hypofibrinogenaemia, maintained for a week, was used to prevent thrombosis on prosthetic heart valves in the calf. Thirteen calves were used in the study. Three of these were used to determine dose schedules and to test antibody formation. The calf was found to have hyperactive fibrinogenesis, and doses higher than previously reported were required to maintain prolonged hypofibrinogenaemia. Antibodies were detected in the calves treated for prolonged periods and the phenomenon was probably related to the massive dosage required. In 10 calves, the tricuspid valve was replaced with a polypropylene valve, using cardiopulmonary bypass. Two of these calves, used as controls and not treated with ancrod, showed massive thrombus formation on the valves. The remaining eight calves were treated with ancrod on different dose schedules. In four calves consistent low fibrinogen levels were not achieved. In the other four, treated by a continuous infusion of ancrod, 8-10 units/kg of body weight per day supplemented further by twice daily intravenous injections of 8·0 units/kg, it was possible to maintain sufficiently low fibrinogen levels and to prevent thrombus formation on the valves. In man, hypofibrinogenaemia is more easily maintained and antibody formation is less likely with the small dosage needed.