Heart | Fetal Arrhythmia
The normal fetal heart has a regular rhythm ranging from 120 -160 beats per minute (bpm). If a fetus’ heart beats at an irregular or abnormally fast or slow rate, serious complications can result.
Essential Information
Overview
Fetal tachyarrhythmias such as fetal supraventricular tachycardia (SVT) or fetal atrial flutter (AF) are heart rhythms where the baby’s heart beats too fast. Without proper treatment, these can result in heart failure and/or fetal hydrops (the accumulation of fluid in multiple cavities within the fetus).
In fetal bradycardias or bradyarrhythmias, the heart beats too slowly. An example of this is “congenital heart block”, which may occur when mothers have certain antibodies in their blood that cross the placenta and interfere with the normal functioning of the electrical conduction system in the heart.
If an abnormal heart rate or rhythm is suspected, the diagnosis should be confirmed with a targeted heart ultrasound – a fetal echocardiogram. Left untreated, these arrhythmias could result in a fetus passing away inside the womb. Ongoing close surveillance in a specialized center is be warranted to ensure that, even if the heart rate returns to normal, the fetus continues to thrive.
Fetal Therapy
If there is a tachyarrhythmia (fast heart rate), mothers can be treated with medications that can cross the placenta to reach the fetal heart. These medications are usually effective at converting the heart beat back to a normal rate and rhythm, and can dramatically improve the outcome both before and after birth. Mothers who are being treated with these medications must be followed closely for side effects, and their fetuses should be monitored closely to ensure that they remain healthy.
If there is a bradyarrhythmia (slow heart rate), sometimes mothers may be treated with medication (steroids or Intravenous immunoglobulin (IVIG)) to decrease damage to the developing fetal heart.
Mothers with either tachy- or bradyarrhythmias may require special management at delivery. Their pregnancies are followed jointly though the fetal medicine unit at Mount Sinai and the fetal cardiac clinic at SickKids and are delivered at Mount Sinai hospital.
Referral Information
Please refer your patient as soon as the diagnosis of a fetal arrhythmia is suspected. Mothers with a significant fetal tachyarrhythmia may be admitted to the antenatal ward at Mount Sinai for monitoring at the start of treatment (typically for less than one week). Regular fetal echocardiographic follow-up will be organized. Local patients will be delivered at Mount Sinai to facilitate postnatal assessment at SickKids hospital.