Table 1.

Differences in Pharmacological Treatment Between the Fetus and Neonate/Infant

	Fetus	Neonate/Infant
Knowledge of treatment of arrhythmias	Limited published experience (<20% of the infant studies), mainly from fetal care centers, within the past 4 decades, even less published for direct fetal therapies	Small to medium case series have been published for most major cardiac drugs used in infants
Pharmacologic assessment	Requires cordocentesis for direct drug measurement; not routine Maternal serum levels and corresponding umbilical cord concentrations can be obtained at delivery Amniotic fluid drug concentration may be higher than maternal serum for some drugs	Serum levels available for digoxin, propranolol, procainamide, flecainide, amiodarone, lidocaine, mexiletine, +/– sotalol Not routinely available for sotalol and beta blockers other than propranolol ECG and heart rate changes used as surrogate to assess drug effect
Electrophysiologic assessment	Maternal home hand‐held Doppler and/or frequent obstetric monitoring critical to detecting SVT recurrence, or bradycardia; if available, fMCG can provide QRS and QTc, HR variability, and STT changes; maternal ECG helpful	Outpatient: Cardiac monitor or Transtelephonic transmitter, Holter monitor, periodic ECGs; transesophageal pacing before discharge may identify fetuses that will never have SVT again and thus do not require treatment or follow‐up
Drug administration	Physiologic changes in later pregnancy (higher cardiac output and volume of distribution), play an important role in transplacental drug delivery; single transplacental drug therapy, followed by combination drug therapy or direct fetal IM or IC therapy No clearly superior first‐line drug for SVT or atrial flutter; currently under study Upward dose adjustment may be needed in the third trimester.	Single drug therapy, followed by dual or combination drug therapy for refractory cases Reduced Compliance with medication administration can be seen if twice‐daily or 4‐times‐daily dosing of drug Drug levels can be used to assess longer‐term compliance; with rapid neonatal/infant growth, drug adjustment every other week is recommended on a mg/kg/day basis. Important to teach neonatal resuscitation to caregivers, and also poison prevention measures for siblings and infant. Maternal postpartum depression can impact medication compliance for infant
Drug withdrawal	Once treatment is initiated, it is usually continued to delivery	Infants after fetal tachycardia should be weaned from treatment at birth unless recent SVT. Most recurrences are within 72 hours. TEP may be useful. If postnatal antiarrhythmics are used, wean off at 6‐12 months of age. Long‐term, if SVT persists, radiofrequency ablation is usually done after 4‐7 years of age
Long‐term prognosis	87% with fetal SVT will wean from drug therapy by 1 year; 13% will still require treatment; higher for those with long‐RP tachycardia	About 90% will wean from therapy; however, late recurrences can be seen in up to one‐third. RF ablation is generally performed over 4‐7 years of age. Younger age risks coronary injury with RF ablation

ECG, electrocardiogram; fMCG, fetal magnetocardiogram; HR, heart rate; IC, intracordal; IM, intramuscular; RF, radiofrequency; SVT, supraventricular tachycardia; TEP, transesophageal pacing.

For references, see text.