Background: Monitoring for fetal supraventricular arrhythmia (SVA) recurrence is essential after pharmacologic conversion to sinus rhythm. Recently, home fetal heart rate and rhythm monitoring (FHRM) by mothers has been reported to successfully detect fetal arrhythmias in anti-Ro/SSA positive pregnancies but FHRM has not been described in fetal SVA.
Objective: To determine: 1. If daily FHRM by mothers detects fetal SVA recurrence; 2. If the dose of antiarrhythmics used to convert SVA can be reduced or the medication changed to maintain sinus rhythm until birth.
Methods: Single center retrospective case series of fetuses with SVA (atrial flutter (AF) and/or supraventricular tachycardia (SVT)) treated with digoxin, flecainide, sotalol, or combination. After sustained sinus rhythm for 1 week or hydrops resolution, maintenance SVA therapy was changed or dose reduced until recurrence or delivery. If mothers detected fetal tachycardia during daily monitoring, an audio text was sent to the physician who increased dosage. Median and range of gestational age (GA) at diagnosis and at conversion, medication change, delivery, and postnatal rhythm were reviewed.
Results: Between 2007 and 2019, 24 fetuses (3 with hydrops and 1 twin) presenting at 29.8 (16.0-35.6) weeks were treated for SVT (n=17) or AF (n=5) or both (n=2). Conversion to sinus rhythm with flecainide (n=4), digoxin (n=4), sotalol (n=3), or combination (n=13) occurred 1.4 (0.0 - 2.9) weeks after diagnosis. Maintenance dose was reduced in all at 1.4 (0.3 - 3.4) weeks after conversion. SVA recurrence during dose reduction was detected by FHRM in 5 fetuses (20.8%). There were no false positives. After recurrence, ambulatory treatment using FHRM restored sinus rhythm 2-4 weeks later in all 5 fetuses. Doses at delivery were 25-100% less than conversion doses. Infants were delivered at 38.9 (34.3-39.6) weeks. SVA recurred in 5 (20.8%) neonates after delivery.
Conclusion: Daily home fetal heart rate and rhythm monitoring by mothers successfully detected SVA recurrence and sinus rhythm restoration. The medication and dose used to convert SVA can be successfully changed or reduced in utero after pharmacologic conversion to sinus rhythm.