Challenges of ICD implantation in patients with adult congenital heart disease may include ana- tomic complexity, intracardiac shunts, and limited vascular access to the ventricle. Patients with adult congenital heart disease receiving an ICD have an increased rate of complications of 26% to 45%, as well as inappropriate shocks in 15% to 25% of Limited studies on the use of subcutaneous implantable cardioverter- defibrillator implantation, particularly in patients with single ventricle anatomy,S10.8-41 report improved success by using right in addition to left parasternal lead positioning for screening.S10.8-42 Patients with a single ventricle or a systemic right ventricle may not tolerate defibrillation thresh- old testing, resulting in multiorgan system fail- ure. Patients with complex anatomy, such as older patients with univentricular physiology, or patients with significantly reduced ventricular function, marked hypertrophy, or multiple prior surgeries, may benefit from earlier consideration of heart transplantation before renal or liver dys- function progresses. 5. Patients with repaired TOF who are at an increased risk of sustained VT include those with prior pal- liative systemic to pulmonary shunts, unexplained syncope, frequent PVCs, atrial tachycardia, QRS duration 180 ms, decreased LVEF or diastolic dysfunction, dilated right ventricle, severe pulmo- nary regurgitation or stenosis, or elevated levels of BNP. Patients with TOF physiology and subop- timal hemodynamic status are more likely to have inducible sustained VT,S10.8-18,S10.8-19,S10.8-33,S10.8-35 and inducible sustained VT correlated with an increased risk of SCA in a multicenter cohort Evaluation of hemodynamics for residual abnormalities is important, with catheter or surgical treatment of important lesions prior to consideration of ICD implantation. 6. In a multicenter cohort, inducible sustained VT in patients with TOF was an independent risk factor for subsequent clinical VT or SCDS10.8-19 ; patients in that early study had cardiomegaly and prior palliative shunts. Patients with repaired Figure 16. 