Treatment, not delivery, of the late preterm and term fetus with supraventricular arrhythmia

Objective: While in-utero treatment of sustained fetal supraventricular arrhythmia (SVA) is standard practice in the previable and preterm fetus, data are limited on best practice for late preterm (34 + 0 to 36 + 6 weeks), early term (37 + 0 to 38 + 6 weeks) and term (> 39 weeks) fetuses with SVA. We reviewed the delivery and postnatal outcomes of fetuses at ≥ 35 weeks of gestation undergoing treatment rather than immediate delivery.

Methods: This was a retrospective case series of fetuses presenting at ≥ 35 weeks of gestation with sustained SVA and treated transplacentally at six institutions between 2012 and 2022. Data were collected on gestational age at presentation and delivery, SVA diagnosis (short ventriculoatrial (VA) tachycardia, long VA tachycardia or atrial flutter), type of antiarrhythmic medication used, interval between treatment and conversion to sinus rhythm and postnatal SVA recurrence.

Results: Overall, 37 fetuses presented at a median gestational age of 35.7 (range, 35.0-39.7) weeks with short VA tachycardia (n = 20), long VA tachycardia (n = 7) or atrial flutter (n = 10). Four (11%) fetuses were hydropic. In-utero treatment led to restoration of sinus rhythm in 35 (95%) fetuses at a median of 2 (range, 1-17) days; this included three of the four fetuses with hydrops. Antiarrhythmic medications included flecainide (n = 11), digoxin (n = 7), sotalol (n = 11) and dual therapy (n = 8). Neonates were liveborn at 36-41 weeks via spontaneous vaginal delivery (23/37 (62%)) or Cesarean delivery (14/37 (38%)). Cesarean delivery was indicated for fetal SVA in two fetuses, atrial ectopy or sinus bradycardia in three fetuses and obstetric reasons in nine fetuses that were in sinus rhythm at the time of delivery. Twenty-one (57%) cases were treated for recurrent SVA after birth.

Conclusion: In-utero treatment of the near term and term (≥ 35-week) SVA fetus is highly successful even in the presence of hydrops, with the majority of cases delivered vaginally closer to term, thereby avoiding unnecessary Cesarean section. © 2023 International Society of Ultrasound in Obstetrics and Gynecology.