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. Atrial tachyarrhythmias occur in up to 60% of adults with Fontan palliation and are associated These arrhythmias may be difficult to manage, are usually poorly tolerated, and cause serious hemodynamic compromise often with dire consequences.S4.4.2-1 Therefore, they should be addressed promptly, including urgent consultation with ACHD provid- ers who can help guide immediate management strategies, even if remotely. Consideration for anti- thrombotic therapy in Fontan patients should take into account the high prevalence of thrombus for- mation and potentially catastrophic impact of pul- monary or systemic thromboembolus. Standard Recommendations for Fontan Palliation of Single Ventricle Physiology (Continued) COR LOE Recommendations CLINICAL STATEMENTS AND GUIDELINES decision-making strategies about rhythm versus rate control or thromboembolic prophylaxis de- rived from and recommended for patients with acquired heart disease and AF do not apply to patients with Fontan physiology, for whom rhythm control and anticoagulation are of greater impor- tance than would be concluded from application of the standard algorithms. Sinus node dysfunction may predispose Fontan patients to atrial tachyarrhythmias, the most common being macro-reentrant circuits or intra-atrial reentrant tachycardia.S4.4.2-13,S4.4.2-47 Nearly 90% of Fontan patients who die from HF have coexisting atrial tachyarrhythmias.S4.4.2-48 Fontan patients are at increased risk of complica- tions from antiarrhythmic therapy, such as tors- ades de pointes with dofetilideS4.4.2-49 and amio- Such agents should be used cautiously and in consultation with ACHD cardiologists and electrophysiology specialists with expertise in ACHD. 2. 