Maternal administration of antiarrhythmic agents has been shown to be effective through transplacental delivery. Flecainide, sotalol, and digoxin, alone or in com- bination, have demonstrated arrhythmia termination rates of 60% to 90%, depending on whether hydrops is pres- In cases refractory to the aforementioned drugs, maternal oral loading for 2 to 7 days with amiodarone may Treatment of fetal SVT has provided safety data for treatment of arrhythmias in women during pregnancy, as addressed in Section 9.3. Figure 18. Acute treatment of atrial flutter. Colors correspond to Class of Recommendation in Table 1; drugs listed alphabetically. *Anticoagulation as per guideline is mandatory. For rhythms that break or recur spontaneously, synchronized cardioversion or rapid atrial pacing is not appropriate. IV indicates intravenous. Figure 19. Ongoing management of atrial flutter. Colors cor- respond to Class of Recommendation in Table 1; drugs listed alphabetically. *After assuring adequate anticoagulation or excluding left atrial thrombus by transesophageal echocardiog- raphy before conversion. Should be combined with AV nodal blocking agents to reduce risk of 1:1 conduction during atrial flutter. AV indicates atrioventricular; SHD, structural heart disease (including ischemic heart disease). Page et al 2015 ACC/AHA/HRS SVT Guideline e549 9.2. Patients With Adult Congenital Heart Disease See Figure 22 for the algorithm for acute treatment of non pre-excited SVT in adult congenital heart disease (ACHD) patients; and Figure 23 for the algorithm for ongoing manage- ment of non pre-excited SVT in ACHD patients. 9.2.1. Clinical Features SVT is observed in 10% to 20% of ACHD patients, and is asso- ciated with a significantly increased risk of heart failure, stroke, The most common mechanism of SVT inACHD patientsismacroreentrantAT(alsocalledflutter),whichaccounts for at least 75% of SVT and frequently involves the CTI. 