A healthy fetus has a heartbeat of 120 to 160 beats per minute, beating at a regular rhythm. Arrhythmia most often refers to an irregular heartbeat, while dysrhythmia represents all types of abnormal heartbeats: the heartbeat can be too fast (tachycardia) or too slow (bradycardia).
How common is it?
Fetal tachycardia, the most common of the rhythm defects, occurs in approximately one in 200 pregnancies.
How is it diagnosed?
Abnormal heart rhythms are diagnosed through ultrasound or fetal echocardiogram. The heart rate can easily be measured and irregular heartbeats can easily be detected; however, the cause of the abnormal rhythm is not always obvious.
What can happen before birth?
Usually, abnormal heart rhythms have little or no effect on the fetus. In rare cases, they can cause heart failure in utero and at birth.
Bradycardia can be a sign of distress for the fetus. When it occurs earlier in pregnancy, it may be the result of other problems and may lead to heart failure and even fetal death. When it occurs toward the end of gestation, urgent delivery may be necessary.
A very fast heart rate may be caused by abnormal firing of the nerves that are responsible for the heartbeat. If the heart beats too fast, contractions are shallow and not enough blood is pumped with each heartbeat. As a result, the fetus can go into heart failure. The most common form of this condition is called supraventricular tachycardia (SVT), in which the heart rate can be faster than 200 beats per minute.
What can be done before birth?
If the fetus does not appear to suffer, an abnormal fetal rhythm is most often closely monitored before birth. If the heartbeat is very fast, such as in SVT, treatment may be necessary. This is typically corrected with medication that you take and pass to your baby through the placenta.
What are my delivery options?
Unless there are signs that the fetus is in trouble, pre-term delivery or Cesarean section is not necessary. Cesarean section may be necessary for obstetrical reasons, however. It is recommended that mothers deliver in a hospital that has immediate access to a specialized neonatal intensive care unit (NICU), with a pediatric cardiologist and other specialists present.
What will happen at birth?
You will most likely be able to hold your baby after delivery. Neonatologists will be present to assess your baby and start treatment if necessary, or bring him or her to the neonatal intensive care unit (NICU).
In most cases, your newborn will receive medications to regulate the heartbeat. In some cases of severe bradycardia, medication alone is not effective and a pacemaker may need to be implanted.
Less commonly, open heart surgery may be necessary to correct the cause of an abnormal heartbeat-for example, by destroying the nerves that are abnormally firing impulses to the heart. In other situations, a newborn may have a structural abnormality and dysrhythmia. These patients often require open heart surgery to repair both problems.
What is the long-term outcome?
The long-term outcome depends on the type of rhythm abnormality and whether other non-cardiac defects are present. Though your baby will need to be on medication to regulate the heartbeat for the first few months of life, most rhythm abnormalities have excellent outcomes.