Fetal supraventricular tachycardia complicated by hydrops fetalis: a role for direct fetal intramuscular therapy.

Maternally administered digoxin for the treatment of fetal supraventricular tachycardia (SVT) complicated by hydrops fetalis may be ineffective secondary to poor transplacental drug transfer. We present our experience with eight pregnancies treated with transplacental therapy or combined maternal and direct fetal intramuscular therapy. Response to treatment following maternal intravenous administration (MIV) of digoxin or a combination of fetal intramuscular (FIM) digoxin and MIV is described for eight hydropic fetuses during nine successful pharmacologic conversions. The MIV digoxin was administered using standard loading and maintenance protocols. FIM was administered at a dose of 88 micrograms/kg q 12-24 hours, to a maximum of three injections in the fetal buttock. Time to onset of the first two hours of sinus rhythm (TO2 degrees), time to onset > 90% sinus rhythm (TO > 90%), and time to resolution of hydrops fetalis (HF) were noted. The mean heart rate was 257 +/- 36 beats/minute and the mean gestational age was 29 +/- 4.8 weeks. Fetal SVT was due to a reentrant mechanism in all cases. For the three fetuses that underwent successful cardioversion following MIV digoxin (all required additional maternal antiarrhythmic drugs), TO2 degrees was 145 +/- 114 hours, TO > 90% was 176 +/- 55 hours, and HF resolved in 41 +/- 37 days. Initial combined FIM and MIV therapy in four fetuses resulted in a TO2 degrees of 5.5 +/- 4 hours, TO > 90% of 22 +/- 14 hours, and resolution of HF in 25 +/- 21 days. For the two failed cardioversions with transplacental treatment alone (one fetus had recurrent SVT with hydrops after initial successful cardioversion with MIV), TO2 degrees was 203 +/- 180 hours and TO > 90% was 313 +/- 270 hours. Once FIM was begun in these fetuses, TO2 degrees was 17 +/- 7 hours and TO > 90% was 60 +/- 13 hours; HF resolved in 45 days in one fetus, whereas the other fetus never had resolution of hydrops despite 100 days of antiarrhythmic therapy. Direct fetal intramuscular injection of digoxin combined with transplacental therapy appears to shorten the time to initial conversion of SVT and to sustain sinus rhythm in the fetus with SVT complicated by hydrops fetalis.