Mitral disc valve implantation in the dog: early and late valve thrombosis and its prevention.

Valve thrombosis and its prevention was studied in 33 Labrador retriever dogs who received Hall-Haster mitral disc valves during extracorporeal circulation with extreme hemodilution. Three antithrombotic regimes were used. (1) 12 dogs received 1 g heparin preoperatively, and Warfarin tablets from the first postoperative day. Anticoagulation was controlled with thrombotest (TT), aiming at 20-25% of normal coagulation activity. (2) 9 dogs received 10 mg of heparin intravenously hourly for 10 h, and intravenous injections of Warfarin daily, aiming at TT values of 15-20%. (3) The last 12 dogs had continuous heparin infusion for 24 h, and Warfarin injections before as well as after the operation in doses sufficient to reduce the TT to 10-15% of normal. Stable anticoagulation was very difficult to maintain. Only 15 dogs survived the first postoperative day, 7 were alive after 4 weeks. 7 early and 5 late deaths were due to valve thrombosis. All three antithrombotic regimes were equally ineffective in preventing thrombosis, and more intensive antithrombotic prophylaxis is needed to make the canine model suitable for experimental open-heart surgery.