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cyanotic heart disease, single or systemic right ventricles, or Ebstein anomaly, is essential to decision making during SVT treatment. In certain conditions, the presence of cyanosis or severe ventricular dysfunction requires consideration of highrisk cardioversion with resuscitation measures at hand; usually, this decision is made at centers with specialized expertise. Management of ACHD patients should be undertaken only in collaboration with a cardiologist who has specialized training or experience in managing such patients. RCTs assessing antiarrhythmic medication efficacy are lacking. Beta-blocking medications offer the advantages of outpatient medication initiation and may provide protection from tachycardia-mediated hypotension or ischemia. Risks of proarrhythmia are increased with the use of sotalol, ibutilide, dofetilide, and particularly flecainide and require in-hospital initiation. Flecainide is associated with increased risk of SCD419 and is reserved for patients without ventricular dysfunction who do not respond to other therapy. 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 physiological 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 reentrant 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 strategy targeting this region is often used. Highest success rates are achieved in patients with atrial septal defects, approaching 90% to 100%, although subsequent AF has been reported in 11% to 30% of patients within 3 years.330,449,458 Because of the need for sophisticated knowledge of anatomy, advanced mapping capability, cardiac anesthesia with careful periprocedural 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 assessment. Intervention for residual hemodynamic/structural defects may need to be planned as part of chronic arrhythmia management. Patients with Ebstein anomaly or repaired tetralogy of Fallot may have significant pulmonary regurgitation, 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 Acute Treatment: Recommendations

Recommendations for Acute Treatment of SVT in ACHD Patients COR LOE Recommendations

I C-LD 1.  Acute antithrombotic therapy is recommended in ACHD patients who have AT or atrial flutter to align with recommended antithrombotic therapy for patients with AF.365

See Online Data Supplements 16 and 17. The risk of stroke associated with AF is well established, and several RCTs have demonstrated the efficacy of anticoagulation for stroke prevention in patients with additional risk factors.366 Anticoagulation has also been shown to prevent stroke when administered during the weeks immediately before and after cardioversion.31,367 Whether atrial flutter carries a risk of stroke similar to that in patients with AF has been debated in the past but is now supported by limited evidence from mechanistic, observational, and prospective studies that include patients primarily with atrial flutter.365–369 Several reports have suggested that the risk of stroke in patients with atrial flutter is mitigated by anticoagulation. Meta-analysis of 13 studies of patients undergoing cardioversion of atrial flutter reported short-term stroke risks ranging from 0% to 7%, and the thromboembolism rate in patients with sustained flutter in 4 studies averaged 3% annually.365 Other studies have reported similar risk and effectiveness of anticoagulation.369 ACHD patients with nonfibrillatory atrial tachyarrhythmias appear to be at high risk, as well.367,459 Therefore, on the basis of available data, recommendations for antithrombotic therapy for ACHD patients who also have AT or atrial flutter are similar to those for patients with AF.10

I B-NR 2.  Synchronized cardioversion is recommended for acute treatment in ACHD patients and SVT who are hemodynamically unstable.75,460

See Online Data Supplement 20. A small observational study demonstrated safety and efficacy of synchronized cardioversion in ACHD patients, with sinus rhythm achieved in 94% of patients.460 Guideline-directed medical therapy supports this treatment approach, stressing that electrical cardioversion is the safest and most effective way of treating SVT associated with hemodynamic instability and should be considered early in the management of such patients.75 Modification of electrode pad placement may be necessary, by using an anterior-posterior configuration in patients with marked atrial enlargement or positioning strategically according to the individual arrhythmia and anatomic substrate, including consideration of the possibility of dextrocardia.

I C-LD 3.  Intravenous diltiazem or esmolol (with extra caution used for either agent, observing for the development of hypotension) is recommended for acute treatment in ACHD patients and SVT who are hemodynamically stable.461,462

See Online Data Supplement 21. Very limited data exist on the use of calcium channel–blocking or beta-blocking medications for rate control or termination of AT or atrial flutter specifically associated with ACHD. Rate control of AT or atrial flutter with rapid AV conduction may be useful to improve hemodynamic status while planning conversion strategies. Patients with congenital heart disease, particularly single-ventricle physiology or systemic right ventricles, may not tolerate ventricular rates >120 bpm for many hours.29 Either drug may be associated with the development of hypotension in up to 20% of patients.462 Because of the high incidence of ventricular dysfunction in this population, particular attention should be given to monitoring the patient for development of hypotension, which would necessitate prompt dose adjustments or change of treatment strategy.

I B-NR 4.  Intravenous adenosine is recommended for acute treatment in ACHD patients and SVT.207,463–465

See Online Data Supplement 20. Observational studies support the use of adenosine to terminate AVNRT, SVT using an accessory pathway, and some forms of focal AT. These mechanisms account for <25% of SVT in adults with repaired congenital disease.207,463 Intravenous adenosine is unlikely to terminate atrial reentry tachycardia or atrial flutter, which represents >70% of SVT episodes in this population, but it may be diagnostic by producing transient AV block, which would make the atrial activity visible.464,465

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