Surgical closure of large ASDs combined with arrhythmia surgery for AT or fibrillation can be safely performed, with 6.5% occurrence of AF reported during 2 years of follow-up.478 IIa B-NR Intravenous ibutilide or procainamide can be effective for acute treatment in ACHD patients and atrial flutter who are See Online Data Supplement 20. A small observational study reported that intravenous ibutilide was successful in conversion of 71% of acute episodes of atrial flutter in ACHD patients; torsades de pointes or nonsustained VT was reported in 2.7% of episodes.468 Pretreatment with magnesium may reduce the incidence of postibutilide ventricular arrhythmias. Small studies support the use of intravenous procainamide as adjunctive therapy for acute therapy of atrial flutter because it improves efficacy of pacing conversion of atrial flutter.466,467 IIa B-NR Atrial pacing can be effective for acute treatment in ACHD patients and SVT who are hemodynamically stable and anticoagulated as per current guidelines for antithrombotic therapy in patients with AF.466,469 472 See Online Data Supplement 20. Small observational studies support the efficacy of atrial pacing to successfully terminate 54% to 82% of acute episodes of AT or atrial Atrial pacing is an effective alternative, particularly when concerns about the use of antiarrhythmic medications or significant sinus node dysfunction exist. IIa B-NR Elective synchronized cardioversion can be useful for acute termination of AT or atrial flutter in ACHD patients when acute pharmacological therapy is ineffective or contraindicated.460 See Online Data Supplement 20. ACHD patients are at increased risk of congestive heart failure and/or atrial thrombus formation with prolonged episodes of AT or atrial flutter. Pharmacological conversion in patients with complex anatomy, ventricular dysfunction, or prolonged QTc intervals may result in significant proarrhythmia or acute hemodynamic deterioration. 