Abnormalities in blood coagulation, fibrinolysis, and platelet activation in adult patients after the Fontan procedure

Background: Thrombosis occurs in up to 30% of patients with various forms of congenital single ventricle after the Fontan procedure. We investigated hemostatic abnormalities in adult Fontan patients. Methods: Forty-eight Fontan patients between ages 18 and 40 years, including 10 (21%) patients with previous thromboembolism 5 to 15 years after surgery, and 35 control subjects matched for age and sex were studied. Coagulation factors and inhibitors, together with markers of fibrinolysis, platelets, and endothelial activation, were determined in peripheral venous blood plasma. Results: Compared with control subjects, Fontan patients showed lower, although mostly within normal ranges, values of all coagulation factors, as well as reduced free protein S, in association with higher antithrombin and free tissue factor pathway inhibitor levels. Thrombin generation, reflected by prothrombin fragment 1.2, and platelet activation markers were increased in Fontan patients. The plasma clot lysis time was prolonged in Fontan patients, which was associated with an increased activity of thrombin-activatable fibrinolysis inhibitor. Fontan patients with previous thromboembolism had lower oxygen saturation, coagulation factors V and VIII, and free protein S, and increased vonWillebrand factor, soluble CD40 ligand, and P-selectin. Other laboratory or clinical parameters were not associated with prior thrombotic episodes. Conclusions: Adult Fontan patients are characterized by enhanced platelet activation and endothelial injury, heightened thrombin formation, and impaired fibrinolysis. Patients showed reduced free protein S levels, increased platelet activation, and endothelial damage after thromboembolic events observed late after Fontan surgery. Our findings indicate novel prothrombotic mechanisms in adult Fontan patients, which might help to optimize thromboprophylaxis.