Flecainide and Digoxin combo Significantly Improves Fetal Tachycardia Treatment Outcomes: Study

A new study published in the journal of Heart Rhythm showed that digoxin monotherapy was effective in only 32% of fetal tachycardia cases, while the addition of flecainide increased the response rate to 93%. Though side effects were more common with combination therapy, they were manageable through dose adjustments. Maternal digoxin levels remained stable throughout pregnancy

When fetal sustained fetal supraventricular tachycardia (SVT) occurs without hydrops, digoxin monotherapy is often started. If hydrops develops or digoxin monotherapy is unable to achieve conversion, flecainide is added. Transplacental antiarrhythmic treatment is necessary for persistent fetal tachycardia. The relationship between dosage, concentration, and effect, as well as the safety of the mother, fetus, and baby, is poorly understood. This study assessed maternal and umbilical cord concentrations, side effects, and the association between the maternal dosage of digoxin and flecainide treatment for fetal tachycardia.

A total of 28 pregnant women who were first treated with digoxin monotherapy for fetal tachycardia between June 2007 and January 2023 were included in this retrospective case series. The relationship between maternal medication exposure, effect, and side effects was the primary goal.

9 (32%) fetuses had sinus rhythm conversion by oral digoxin monotherapy after a median of 4.5 days (IQR 3-6.5). The total conversion rate was 93% (26/28), with 18 fetuses requiring extra oral flecainide (300 mg daily). Regardless of gestational age, maternal digoxin concentrations were identical for responders and non-responders with equal initial digoxin dosages (p=0.504). Doses were lowered due to side effects, mostly nausea, but the treatment was still successful.

Throughout pregnancy, maternal digoxin levels were consistent, and there was minimal variation across patients. Exposure to flecainide differed across and between subjects. Both the monotherapy (n=3) and combination (n=9) treatment groups had comparable median fetus/mother digoxin ratios (0.51 (IQR 0.28-0.76) vs. 0.45 (IQR 0.39-0.64), p=0.864). The median flecainide ratio between the mother and fetus was 0.82 (IQR 0.69-1.29).

Overall, important new information on the pharmacological therapy of fetal tachycardia has been added by the current study, which involved a bigger patient cohort. Digoxin and flecainide together are more effective than digoxin alone, but they also cause greater adverse effects, according to one study.

Source:

Smeets, R. M. A., van Beynum, I. M., van Kesteren, C., Cornette, J. M. J., van der Zande, J. A., Roos-Hesselink, J. W., Beex-Oosterhuis, M. M., & Flint, R. B. (2025). The maternal exposure of digoxin and flecainide in relation to the safety and effectiveness in the treatment of non hydropic fetal tachycardia. Heart Rhythm: The Official Journal of the Heart Rhythm Society. https://doi.org/10.1016/j.hrthm.2025.05.039