High-dose flecainide is the most effective treatment of fetal supraventricular tachycardia.

Background: Fetal tachyarrhythmia can lead to fetal hydrops due to heart failure. Flecainide is often considered as second-line therapy when digoxin monotherapy fails, which is more likely in hydropic fetuses. Time to conversion to sinus rhythm (SR) is critical in cases presenting with hydrops.
Objective: The aim of this study was to evaluate the efficacy and time to conversion to SR of transplacental treatment, especially flecainide.
Methods: This is a retrospective observational study of 46 fetuses with fetal tachyarrhythmia. Treatment was either flecainide (n = 28, 60.9%), digoxin+flecainide combination (n = 4, 8.7%), or digoxin (n = 10, 21.7%). In 4 fetuses (8.7%), no treatment was necessary.
Results: In our study population, 26 of the 32 fetuses (81.2%) that were treated with flecainide as a first-line therapy (flecainide or digoxin+flecainide) converted to SR. The median time to conversion to SR was 3 days (range 1-7 days) with flecainide monotherapy and 11.5 days (range 3-14 days) with a combination therapy. Seventy-two percent (13/18) of hydropic fetuses and 90% (9/10) of nonhydropic fetuses converted to SR when treated with flecainide monotherapy. There was no statistical difference in rates of conversion to SR in hydropic and nonhydropic fetuses (P = .37) or time to conversion to SR in the 2 groups (P = .9). In the majority of the remaining fetuses, there was a partial response with decreased ventricular heart rates that were well tolerated.
Conclusion: Flecainide is highly effective in achieving SR in hydropic and nonhydropic fetuses with supraventricular tachycardia in a median time of 3 days. In our opinion, flecainide should be considered as first-line therapy in fetal supraventricular tachycardia with and without hydrops.
(Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)