Conversion to a total cavopulmonary connec- tion Fontan combined with a modified right atrial Maze procedure may be considered in patients with symptomatic refractory recurrent intra-atrial In the pres- ence of documented AF, a left atrial Cox Maze procedure may also be indicated.S4.4.2-16,S4.4.2-62 Some patients may not be appropriate surgical candidates for reasons of elevated PA or Fontan pressures, elevated ventricular end-diastolic pres- sures, or renal or hepatic dysfunction, and the de- cision to perform Fontan revision surgery is rarely straightforward. 14. Pulmonary vasoactive medications, specifically endothelin receptor antagonists and PDE-5 inhibitors, are of increasing interest as a means of reducing pulmonary vascular resistance and improving cardiac output. In limited studies, use of PDE-5 inhibitors appears favorable for Fontan patients with improvement noted in pulmonary blood flow and exercise capacity.S4.4.2-21,S4.4.2-63 Use of endothelin antagonists has been investigated in a randomized trial.S4.4.2-19 After 14 weeks of ran- domization in 69 subjects successfully completing the study, there was a modest but significant in- crease in peak oxygen consumption and exercise duration in those taking bosentan compared with those on placebo. 15. Although anticoagulation is prudent in those with prior arrhythmia or known thromboem- bolic events, routine use of anticoagulation with vitamin K antagonist cannot as yet be strongly recommended. An RCT in Fontan children/ado- lescents did not show benefit,S4.4.2-64 although adults later after Fontan may be more at risk. 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. 