However, residual hemodynamic and electro- physiological abnormalities are common in adulthood. Adults with repaired TOF face an increased risk of ar- rhythmias, exercise intolerance, HF, and death begin- ning in early adulthood.S4.3.5-1,S4.3.5-18 S4.3.5-20 Surgical re- pair of TOF has evolved over time, with relief of the RVOT obstruction usually involving infundibulotomy, resection of obstructive muscle bundles, and the use of a patch to enlarge the pathway from the right ventricle to the pulmonary arteries. These procedures result in scar tissue and create a dyskinetic and often aneurys- mal area in the RVOT. Residual RVOT stenosis, branch PA stenosis, residual ASD or VSD, TR, RV dilation and dysfunction, aortic dilation, AR, and LV dysfunction are some of the anatomic and functional abnormalities en- countered in patients with repaired TOF. The most com- mon hemodynamic sequela of TOF repair is PR. Cur- rent evidence confirms that adults with repaired TOF are at risk of severe PR, RV dilation and dysfunction, LV dysfunction and electromechanical dyssynchrony, all of which contribute to adverse clinical outcomes late after TOF repair.S4.3.5-1,S4.3.5-20 S4.3.5-24 Despite intense in- terest and numerous publications on pulmonary valve replacement in adults with repaired TOF, optimal tim- ing for this intervention remains uncertain, and most studies have focused on preoperative RV volumes that would result in normalization of postoperative RV In adults with repaired Recommendations for TOF (Continued) COR LOE Recommendations CLINICAL STATEMENTS AND GUIDELINES TOF, prevalence rates for atrial and ventricular arrhyth- mias have been estimated to be 20% and 15%, respec- tively, with steep increases after 45 years of age.S4.3.5-28 The incidence of SCD after surgical repair of TOF is Currently, factors associated with SCD in patients with TOF have largely been identified from observa- tional, predominantly retrospective studies. 