Thrombosis of the Björk-Shiley prosthesis: illustrative cases and review of the literature.

Thrombosis of the Björk-Shiley prosthetic cardiac valve may occur in any valve position and regardless of anticoagulant status. Four illustrative cases are presented to demonstrate management problems. Review of cases reported in the literature suggests the minimal incidence of thrombosis of Björk-Shiley prostheses is about 2% in the aortic position and about 4% in the mitral position. Prevention of this complication appears to require continuous systemic anticoagulation with warfarin; even temporary interruption or alteration of anticoagulant regimen may be detrimental. Although changes in anticoagulation may rarely precipitate sudden thrombosis, in most cases a period averaging 10 months is required for pannus of organized thrombus to build up enough to cause acute thrombosis and malfunction of the valve. Operation to remove thrombus or replace the prosthesis is usually required for left-sided cardiac prostheses, but thrombosed valves in the tricuspid position may be successfully treated with fibrinolytic medical therapy.