Transplacental Flecainide and/or Digoxin for Fetal Tachyarrhythmias: Therapeutic Efficacy and Clinical Experience

To assess the efficacy and safety of transplacental flecainide and/or digoxin for fetal tachyarrhythmias when sotalol is unavailable.

We evaluated transplacental flecainide, digoxin, or combination therapy in a retrospective and prospective cohort across two Thai tertiary centers. Outcomes were classified as complete cardioversion, partial response (rate control), or treatment failure.

Of 24 eligible pregnancies, 14 (58.3%) had supraventricular tachycardia (SVT), 8 (33.3%) had atrial flutter (AFL), and 2 (8.3%) had ventricular tachycardia (VT). Overall, clinical responses occurred in 91.7% (22/24) of fetuses. Flecainide monotherapy achieved 100% (9/9) complete cardioversion in SVT, compared with 50% (1/2) for digoxin. SVT combination therapy (n = 3) yielded 1 complete and 1 partial response. Among 7 flecainide-treated AFL cases, 5 (71.4%) achieved rate control and 2 (28.6%) achieved cardioversion; one digoxin-treated case fully converted. Flecainide resolved 1 of 2 VT cases (50%). Response rates were unaffected by hydrops, gestational age, or cardiac defects (p = 0.087-1.000). Maternal adverse events were mild and required no treatment discontinuation.

Transplacental flecainide demonstrates high efficacy in SVT and effective rate control with preserved cardiac function in AFL. Its favorable safety profile makes it a practical alternative for first-line therapy where sotalol is unavailable and flecainide monitoring is infeasible.