A prospective study of platelet metabolism in rheumatic heart disease. Effect of prosthetic heart valve.

The metabolic activity of platelets in patients with advanced rheumatic heart disease (RHD) was estimated by measurement of heat production in a microcalorimeter. Twenty-nine patients were randomly selected and prospectively followed before and after valve replacement with Björk-Shiley prosthesis. Before the operation a significantly (P less than 0.02) elevated platelet heat production was found compared with normal subjects, 63 +/- 5 fW/cell and 59 +/- 4 fW/cell, respectively, probably due to the presence of a younger and metabolically more active platelet population. Platelet count before the operation was significantly lower than normal (P less than 0.001). Platelet heat production did not correlate with either type of valvular disease, the presence of valvular calcification or atrial fibrillation. After valve replacement the platelet heat production significantly decreased (P less than 0.001) to 58 +/- 5 fW/cell and the platelet count normalized. The highest incidence of thromboembolic manifestations was in the immediate postoperative period. The greatest reductions in platelet heat production. 19% and 27% were observed in two patients with thromboembolic events, as compared with an average of 4% for the rest of the operated patients without complications. The possible relationship between changes in platelet heat production and thromboembolism in patients with RHD is discussed.