RESUMEN
Fetal tachycardia is mostly benign, but sometimes results in serious consequences such as fetal hydrops and fetal death. To decrease cardiovascular burden, fetuses could be treated with transplacental administration of antiarrhythmic drugs such as digoxin, amiodarone. Although amiodarone has been proven to be effective against fetal tachycardia, it is also known to cause transient neonatal thyroid dysfunction and neurodevelopmental delay in some patients. Nonetheless, there has been only few postnatal follow-up studies with the patients who were diagnosed and treated for fetal tachycardia although majority of postnatal arrhythmias occurred within the first 48 hours of life in a recent report. We report a newborn with transient thyroid dysfunction and late-onset supraventricular tachycardia at 1 month age, who had fetal tachycardia treated with amiodarone at the 25th week of pregnancy.