Prenatal ultrasound showing fetal tachycardia (2024)

This information sheet from Great Ormond Street Hospital (GOSH) explains about fetaltachycardia detected during a prenatal ultrasound scan and what this might mean for yourchild. It will support the information discussed with you by your doctor and nurse at yourappointment and it is important to remember that every case is slightly different.Tachycardia is an abnormally fast heart rate. Thenormal fetal heart rate is between 120 and 160beats per minute. Typically, an abnormally fastheart rate is over 200 beats per minute.

The heart is made up of four chambers – two atthe top called atria and two at the bottom calledventricles. The ventricles are the pumping chambersof the heart. It is the top two chambers of theheart (atria) that set the pace of the heart, andnormally the ventricles only respond to electricalimpulses from the atria.

In some fetuses, the atria and ventricles are bothbeating fast but at the same rate (supraventriculartachycardia). In others, the atria beat exceedinglyfast (over 300 beats per minute), much fasterthan the ventricles (atrial flutter). Other rhythmdisturbances may occur but are much rarer.

In most cases we can reduce the fast heart rateby giving medication to the mother, which passesthrough the placenta to the baby.

We perform a simple test on the mother’sheart called an electrocardiogram (ECG) beforeprescribing the medication. Some stickers will beapplied to the chest to check your heart rhythmand that it is safe to give you the medication. Somemedications can take two to three weeks beforethey are effective in reducing a baby’s heart rate.

Usually treatment is given as an outpatient anddoes not need a stay in hospital. However, we willmonitor you and your baby’s heart rate regularlywhen you first start taking it.The aim of treatment is to control the rhythmof the baby’s heart, which in most cases allows anormal birth at term (after 37 weeks). We mayneed to take blood samples from you to check thelevels of the medication in your body to make surethat they are within the correct range.

Occasionally, we may have to try more than onemedication before we are able to reduce thebaby’s tachycardia. The type of treatment selecteddepends on a number of factors including the typeof the tachycardia, how many weeks pregnant youare, and if there are signs of hydrops. We may need to reassess treatment if medicationis not effective in reducing your baby’s heart rate.

Each case may differ slightly and the consultantswill talk to you about management of your baby’sfast heart rate during your appointments at GOSH.There are rare occasions where, despite medication, itmay not be possible to reduce the fast heart rate andit may remain high for the rest of the pregnancy.

In the majority of cases, a normal delivery at yourlocal hospital is possible. During labour, a baby’sheart rate is monitored for signs of stress. If yourbaby’s heart rate is already high, this can make itdifficult for the labour team to monitor your baby’swell-being.

Your obstetric team and the fetal team at GOSHwill discuss the safest mode of delivery for you andyour baby, and this may include the possibility ofearly delivery (before 37 weeks) or a Caesareansection may be advised.

After birth, babies usually do very well eventhough you took medication during pregnancy.After your baby is born, we recommend that theyhave an electrocardiogram (ECG) to check theirheart rhythm. The doctors looking after your babywill then talk to you about whether any furthertreatment or monitoring is needed. The causes ofyour baby’s tachycardia will be investigated andmay require further treatment.

Your baby’s fast heart rate is likely to continueafter birth, but in some cases the tachycardia canslow down to a normal rate by itself. In eithersituation, a period of monitoring will be requiredand in most cases medications are still used tocontrol the fast heart rate.

Your baby will be referred to a paediatriccardiologist who will review your baby, ECGand ECHO results and will help to manage themedications your baby needs. Occasionally morethan one medication is required.

Disclaimer