Sinus node dysfunction may contribute to the development of atrial arrhythmias and may become exacerbated with antiarrhythmic medications. Atrial antibradycardia pacing to maintain a consistent physi- ological heart rate may decrease the frequency of tachycardia episodes and may improve functional capacity.364,370,371 Atrial antitachycardia pacing to terminate atrial reentry tachycardia is an effective approach when feasible.364,370,371 Overall acute success rates of catheter ablation procedures for SVT in ACHD patients range from 70% to 85%, with recurrences in 20% to 60% of patients within 2 years.452 457 Catheter ablation is challenged by limitations of venous access to the heart, hypertrophied atrial tissue, multiple atrial reen- trant circuits, and atrial baffles partitioning the coronary sinus and CTI to the pulmonary venous atrium. Because the CTI is involved in >60% of atrial reentry circuits, an initial strat- egy targeting this region is often used. Highest success rates are achieved in patients with atrial septal defects, approach- ing 90% to 100%, although subsequent AF has been reported Because of the need for sophisticated knowledge of anatomy, advanced mapping capability, cardiac anesthesia with careful peripro- cedural monitoring, and repeat ablations, such patients should be referred to centers with extensive experience in complex congenital heart disease ablations. The development of atrial arrhythmias in ACHD patients is often an indicator of progressive hemodynamic changes, which require in-depth functional and hemodynamic assess- ment. Intervention for residual hemodynamic/structural defects may need to be planned as part of chronic arrhyth- mia management. Patients with Ebstein anomaly or repaired tetralogy of Fallot may have significant pulmonary regurgita- tion, tricuspid regurgitation, or both, which might benefit from reoperation. In some settings, integration of operative ablation techniques with hemodynamic repair may be optimal. 9.2.2. 