However, a secondary analysis of that RCT as an found the risk of throm- boembolism was lower in those patients on war- farin who consistently achieved minimum target international normalized ratio levels, as well as in those on acetylsalicylic acid compared with patients who often failed to meet target interna- tional normalized ratio level. Rates of thrombosis were considerably higher in patients on warfarin who did not consistently achieve target inter- national normalized ratio. A study of modes of CLINICAL STATEMENTS AND GUIDELINES death in atriopulmonary Fontan patients dem- onstrated lower rates of death in patients on some antiplatelet agent or anticoagulation compared with those on none.S4.4.2-1 Direct oral anticoagulants are unstudied and thus cannot be recommended at the present time. There are con- cerns about liver function vulnerability in Fontan patients, which theoretically may increase the risk of complications with some of those agents. 16. There are occasions where surgery or catheter intervention may be alternatives to transplanta- tion for a failing Fontan after weighing risks and benefits of the intended procedure (ie, alle- viation of atrioventricular valve regurgitation, sys- temic or pulmonary venous pathway obstruction). Reoperation for atrioventricular valve regurgita- tion may be high-risk, particularly when systemic ventricular function is impaired. Although valve repair is preferred and operative risk is usually lower, it is not always possible. Risk of valve re- placement in this setting is high. 4.4.3. 