Prolonged Resolution of Intrauterine Fetal Tachyarrhythmia Treatment

Fetal tachyarrhythmia is a rare condition associated with a high risk of fetoplacental circulatory failure, fetal hydrops, and intrauterine fetal death. This report, present a case of fetal tachyarrhythmia that was successfully managed with a multidisciplinary approach in a tertiary hospital, but with prolonged prenatal resolution. A 36-year-old multigravida was diagnosed with fetal tachyarrhythmia at 30 weeks of gestational age. No secondary cause of fetal tachyarrhythmia was identified. A basic ultrasound examination revealed a normal heart structure without hydrops or polyhydramnios. The fetal heart rate was consistently at 230 bpm during the examination. M-mode echocardiography presented the 1:1 atrioventricular contraction with short intervals, confirming the diagnosis of sustained supraventricular tachycardia. Transplacental treatment was initiated using digoxin at a dose of 0.5 mg, followed by 0.25 mg intravenously every 8 hours. On the fifth day, the arrhythmia was not improved, thus oral combination therapy commenced with digoxin at a dose of 0.25 mg every 12 hours, along with propranolol at a dose of 40-20-20 mg, and this treatment was continued for the subsequent 5 weeks. Fetal heart rate, movement, and treatment toxicity were monitored daily, while fetal well-being was assessed on a weekly basis. Prenatal resolution was achieved 6 weeks after the treatment initiation. Digoxin levels reached a therapeutic concentration (1.75 ng/mL) without any signs of intoxication. A cesarean section was performed at 38/39 weeks of gestational age. The postnatal evaluation did not reveal any recurrence of tachyarrhythmia or neurodevelopmental disorders. Evaluation of atrioventricular contractions using M-mode echocardiography proved to be a straightforward method. In this case of sustained supraventricular tachycardia, the absence of fetal hydrops was likely attributed to ventricular contractions remaining below 230 beats per minute. The use of combination therapy demonstrated superiority over monotherapy in achieving prenatal resolution. Transplacental anti-arrhythmic combination therapy can be considered for cases of refractory tachyarrhythmia. Further large-scale population studies are necessary to determine appropriate therapeutic doses and adjust available drug options to achieve faster prenatal resolution of fetal tachyarrhythmias.