Management of supraventricular tachycardia diagnosed at 12 w
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Supraventricular tachycardia (SVT) is the most common type of fetal tachycardia. Left untreated, SVT can lead to hydrops and in utero demise. In most cases, diagnosis is made after the first trimester. The literature is scarce concerning the appropriate management of SVT diagnosed during the first trimester.

A 30-year-old woman, G3P2, presented at 12 weeks for her first trimester ultrasound which revealed a severe tachycardia (292 bpm). Nuchal translucency and fetal anatomy were normal. There were no signs of hydrops. Her first trimester work up was normal and cell free DNA testing indicated a low risk for Trisomy 21. The patient was transferred in emergency, fetal echocardiography at 12 weeks confirmed the diagnosis of SVT. Flecainide 100mg three times daily was initiated and normal fetal heart rhythm was restored 48h later. Serial biweekly follow up ultrasounds continued to show normal rhythm. At 20 weeks, a small muscular ventricular septal defect (VSD) was diagnosed. Because of worsening maternal side effects, flecainide was tapered. There was no recurrence of abnormal fetal heart rhythm. At 39 weeks, she delivered a baby girl weighing 3,790g and with an Apgar score of 9-9-9. Postnatal echocardiography confirmed the VSD and diagnosed a type 2 atrial septal defect. Electrocardiogram was normal.

This is one of the first cases of fetal SVT diagnosed and treated during the first trimester. Although the exact etiology remains speculative, treatment with flecainide was effective and lead to a good outcomes. Measurement of fetal heart rate during the first trimester is essential for early diagnosis of SVT without hydrops.

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