Endothelin antagonists have been studied in a single RCT, which showed improved exercise capacity in 75 subjects randomized to bosen- tan compared with placebo.S4.4.2-19 Two other small non- randomized studies demonstrated minimal response to Corticosteroids, specifically budesonide, may be helpful for Fontan patients with hypoalbuminemia in the setting of protein-losing enteropathy poorly re- sponsive to other therapies. Budesonide seems to have fewer systemic effects than other oral steroids; how- ever, close monitoring for signs of hypercortisolism Octreotide may be con- sidered; it is a therapy with favorable but very limited anecdotal experience reported, with further research A combination of these therapies may be applied in an affected patient, as such strat- egies collectively appear to have produced improved outcome compared with historic controls.S4.4.2-31 Fontan surgery has been associated with prolonga- tion of atrial refractory periods, extensive atrial scar- ring, and intra-atrial conduction delay.S4.4.2-32 S4.4.2-38 Si- nus node dysfunction occurs in up to 45% of adults during long-term follow-up after Fontan surgery and has been associated with a reduction in preload to the single ventricle, increased pulmonary venous pres- sure, reduced cardiac output, plastic bronchitis, and Transvenous atrial pacing may be feasible in most adults with atrio- pulmonary Fontan connections and in some with intra- cardiac lateral tunnels,S4.4.2-44 although the potential for thrombotic complications must be addressed. Ventric- ular pacing may be performed via the coronary sinus in selected patients, but most require an epicardial Management of atrial arrhyth- mias is discussed in the associated recommendations. See Section 3.3 for recommendations on who should perform surgeries, cardiac catheterization and other procedures in these patients; Section 3.4 for rec- ommendations on diagnostic evaluation; and Table 32 for routine testing and follow-up intervals. Recommendation-Specific Supportive Text 1. 