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

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