Observational studies reported thyroid disorders in 13% to 36% of ACHD patients receiving amiodarone; risk factors for thyrotoxicosis include female sex, cyanotic heart disease, low body mass index, prior Fontan procedure, or dosages >200 mg daily.511,512 Amiodarone is recommended for short-term use or for patients for whom alternative therapy is not an option for prevention of recurrent AT. III: Harm B-NR 1. Flecainide should not be administered for treatment of SVT in ACHD patients and significant ventricular dysfunction.419 See Online Data Supplement 20. There are no RCTs on the use of flecainide in ACHD patients and ventricular dysfunction. One retrospective study collected data on 579 young patients, 369 of whom received flecainide for the treatment of SVT. Efficacy for the treatment of SVT was 71%. Among 12 patients with cardiac arrest while receiving flecainide for SVT, 8 had congenital heart disease, and 7 of 8 had either mild to moderate ventricular dysfunction or systemic right- or single-ventricle anatomy. The risk associated with flecainide treatment of SVT associated with congenital heart disease appears to be highest among patients with complex heart disease or ventricular dysfunction. Recommendations for Ongoing Management of SVT in ACHD Patients (Continued) COR LOE Recommendations Recommendations for Acute Treatment of SVT in Pregnant Patients COR LOE Recommendations I C-LD 1. Vagal maneuvers are recommended for acute treatment in pregnant patients with SVT.235,516 See Online Data Supplement 20. For acute conversion of SVT, vagal maneuvers, including Valsalva and carotid sinus massage, can be performed quickly and should be the first-line intervention to terminate SVT. These maneuvers should be performed with the patient in the supine position. Vagal maneuvers typically will not be effective if the rhythm does not involve the AV node as a requisite component of a reentrant circuit. 