Objectives: To assess the efficacy of flecainide in the intrauterine treatment of fetal supraventricular tachycardia (SVT) with 1 : 1 atrioventricular conduction.
Design: Twenty fetuses (21-35 weeks of gestation) with SVT ranging between 215 and 280 bpm were analyzed retrospectively. Fetuses received flecainide and digoxin as either first, second or third line therapy. Intracardiac blood flow, venous Doppler waveforms and cardiotocograms were evaluated before and after drug induced conversion to sinus rhythm.
Results: After initiation of combined flecainide and digoxin therapy, the median time interval until final conversion to sinus rhythm was 5 days (range, 0-14 days). The majority of fetuses (n = 15; 75%) converted to sinus rhythm within 7 days of treatment, whereas the remaining five (25%) showed initial reduction of the heart rate to 160-215 bpm over several days, with restoration of a triphasic venous blood flow pattern before late conversion within 7-14 days after initiation of flecainide treatment. One of these fetuses showed a decrease in fetal heart rate to 160-190 bpm without conversion to sinus rhythm but with resolution of hydrops. All fetuses survived.
Conclusions: Flecainide is safe and highly effective in the intrauterine treatment of hydropic fetuses with supraventricular tachycardia. Conversion into sinus rhythm can be expected 72 h after initiation of therapy but may take up to 14 days. Therefore therapy should be continued beyond 72 h, especially when an initial decrease of fetal heart rate is observed which may represent an early therapeutic response.