Fetal Cardiac Arrhythmia

What is Fetal Arrhythmia?

Fetal arrhythmia refers to an irregular heartbeat or an abnormal heart rhythm in an unborn baby (fetus). Normally, a fetus' heart rate is steady and falls within a certain range. Fetal arrhythmias can lead to changes from this regular pattern. These irregularities can be a heartbeat that is too fast (tachycardia), too slow (bradycardia), or irregular in its rhythm (extra beats or skipped beats).

Normal Fetal Heart Rate vs. Abnormal Fetal Heart Rate

A normal fetal heart rate (FHR) is typically between 120 and 160 beats per minute (bpm) during the second and third trimesters of pregnancy. The FHR can fluctuate based on various factors, including the baby's activity, maternal activity, and gestational age (how far along a pregnancy is). 

For example, the average FHR is higher at an early gestational age, and FHR can temporarily become faster with active fetal movements. Isolated changes in the fetal heart rate do not necessarily indicate a serious problem. Fetal heart rates can vary throughout the day and in response to fetal movement or contractions.

Fetal bradycardia refers to a heart rate that is lower than expected range for the gestational age. Although the normal range can vary based on the gestational age, FHR consistently below 120 bpm is considered abnormal. This can be a concern, especially if it is severe or persistent.

Fetal tachycardia refers to a FHR which is too fast, typically when the heart rate consistently exceeds 160 bpm.

How Common is Fetal Arrhythmia?

Fetal arrhythmia is relatively uncommon, occuring in approximately 1% of pregnancies. 

Types of Fetal Arrhythmia

There are several types of fetal arrhythmias, each characterized by different patterns of heartbeats. Common types include:

  • Premature Atrial Contractions (PACs): PACs are early heartbeats that originate in the atria (the upper chambers of the heart). They are one of the most common types of fetal arrhythmias and are usually benign. PACs usually present as irregular fetal heart beats found during fetal ultrasound or fetal heart tone checks. In many cases, PACs resolve on their own. Rarely, fetuses with frequent PACs can develop more significant fetal arrhythmia in form of supraventricular tachycardia (see below), which occurs in approximately 2%-3% of pregnancies affected by PACs. A fetal echocardiogram and consultation with a fetal cardiologist can be useful when PACs are suspected.

  • Supraventricular Tachycardia (SVT): SVT is characterized by an abnormally fast heart rate. This may originate in the atria or can be due to an abnormal electrical circuit between the upper chambers (atria) and lower chambers (ventricle). It can cause a rapid and sustained increase in the fetal heart rate often at rates well above 200 bpm.

  • Atrial Flutter (AF): AF is an abnormally fast heart rate where the upper chambers (atria) beat at 2 to 3 times the rate of the lower chambers (ventricles). Atrial rates are often 300-500 bpm.

  • Atrioventricular Block (AV Block): AV block refers to a delay or blockage in the electrical signals between the atria and ventricles. It can manifest as first-degree, second-degree, or third-degree (complete) block, depending on the severity. Third-degree AV block is the most concerning.

  • Sinus Bradycardia: Sinus bradycardia is characterized by a slower-than-normal heart rate and can be caused by both cardiac electrical problems and other fetal abnormalities.

  • Sinus Tachycardia: Sinus tachycardia occurs when the fetal heart rate is faster than normal, but is not a true arrhythmia. It can result from various factors, including maternal (fever, stress, medications) or fetal (stress, anemia).

Causes of Fetal Arrhythmia

Fetal arrhythmias can occur for various reasons. Some common causes and contributing factors of fetal arrhythmia include:

  • Heart Problems: Sometimes, the baby's heart may not develop as it should. This can lead to abnormal heart rhythms.
  • Maternal Health: Certain conditions in the mother, like diabetes, thyroid issues, or infections, can affect the baby's heart rate.
  • Medications: Some medicines that the mother takes during pregnancy can influence the baby's heart rate or rhythm.
  • Unknown Reasons: In some cases, doctors may not know exactly why it happens.

It is important to note that the causes of fetal arrhythmias can vary widely, and in many cases, the exact cause may not be immediately apparent.

Detection & Diagnosis of Fetal Arrhythmia

Fetal arrhythmia can be detected and diagnosed through a combination of prenatal monitoring and diagnostic tests. The process typically involves the following steps:

  • Routine Prenatal Checkups: Early and regular prenatal care is essential. Your care team can often detect fetal arrhythmia during regular checkups. They listen to the baby's heartbeat with a special device or monitor it over time using electronic equipment.

  • Fetal Heart Rate Monitoring: If a healthcare provider detects an irregularity during routine checkups or if the pregnant individual reports unusual fetal movements or sensations, they may recommend continuous fetal heart rate monitoring or intermittent home monitoring. This involves the use of an electronic fetal monitor (EFM) or cardiotocograph (CTG) to record the baby's heart rate over a set period of time. This monitoring can help identify persistent arrhythmias.

  • Ultrasound: Prenatal ultrasound is a valuable tool for assessing fetal development, including the heart. During an ultrasound examination, a care team can visualize the baby's heart, measure its size, and assess its function. They may look for structural heart defects and evaluate blood flow through the heart and surrounding vessels.

  • Fetal Echocardiogram (Fetal Echo): If a fetal arrhythmia is suspected or detected during routine monitoring or ultrasound, a fetal echocardiogram may be recommended. This specialized ultrasound of the fetal heart provides detailed images of the heart's structure and function allowing pediatric cardiologists to assess the type and severity of the arrhythmia as well as any affects the arrhythmia has had on the heart.

  • Maternal Monitoring: In some cases, maternal monitoring is necessary to assess whether maternal conditions, such as fever or infection, are contributing to the fetal arrhythmia. Treating the underlying maternal condition may resolve the arrhythmia.

  • Blood Tests: Blood tests may be performed to check for factors like fetal anemia or maternal thyroid dysfunction, which can contribute to fetal arrhythmias.

  • Genetic Testing: In some cases, genetic testing may be considered to evaluate for genetic factors associated with certain types of arrhythmias. Genetic counseling may be beneficial to assess the risk of passing on conditions within families. 

Once a fetal arrhythmia is detected and diagnosed, the healthcare team, which often includes pediatric cardiologists and maternal-fetal medicine specialists, will determine the appropriate management and treatment plan.

Potential Complications of Fetal Arrythmias

Fetal arrhythmia can sometimes lead to complications:

  • Less Oxygen: The baby might not get enough oxygen if the heart isn't working properly.
  • Heart Problems: In severe cases, the baby's heart might not pump blood well, which can lead to heart problems.
  • Preterm Birth: In some situations, the baby might need to be delivered early to treat the condition.

Treatment of Fetal Arrhythmias

Doctors can often manage and treat fetal arrhythmia. The treatment depends on what is causing the problem and how severe it is. It might involve medications or more advanced procedures.

Why Choose Lurie Children’s for Treatment?

Lurie Children’s Fetal Cardiology team works alongside our pediatric heart rhythm specialists (electrophysiologists) as well as our maternal-fetal-medicine and adult cardiology colleagues at Northwestern Medicine to provide comprehensive care to all individuals whose pregnancies are complicated by fetal arrhythmias.

Our team is available 24/7 when issues arise to provide rapid assessment that allows for immediate intervention, if necessary. Our Fetal Cardiology team provide services at The Chicago Institute for Fetal Health as well as at Prentice Women’s Hospital for both inpatient and outpatient evaluation.

Our team is also actively involved in research and publishing in medical journals to advance the field of fetal arrhythmia diagnosis and treatment. Some of our publications include: 

Long-Term Outlook for Patients with Fetal Arrhythmia

Advancements in medical technology and healthcare have significantly improved the prognosis and quality of life for individuals with fetal arrhythmia. Many can lead healthy and fulfilling lives with proper medical management and support.

The long-term outlook is best discussed with a pediatric cardiologist who can provide personalized guidance based on the specific circumstances of the individual's condition. 

Other Frequently Asked Questions

Can Fetal Arrhythmias Be Prevented?

Not all cases of fetal arrhythmia are preventable. Some may be due to congenital factors that are beyond control. Additionally, some arrhythmias may arise spontaneously without a known cause.

Can Fetal Arrythmias Affect Labor and Delivery?

Fetal arrhythmias can potentially affect labor and delivery, although the impact varies depending on the type and severity of the arrhythmia, the overall health of the baby, and other factors.

Some ways in which fetal arrhythmias can influence the labor and delivery process include:

  • Timing of Delivery: In some cases, healthcare providers may recommend early delivery (before the due date) if the fetal arrhythmia is severe and poses a significant risk to the baby's health.

  • Mode of Delivery: If properly managed during pregnancy and time of delivery, the majority of fetal arrhythmias do not typically dictate the mode of delivery (vaginal delivery or cesarean section). Mode of delivery is often based on other factors such as the baby's position, maternal health or other considerations. However, if the fetus is in sustained tachycardia or bradycardia, fetal monitoring during vaginal delivery becomes challenging, requiring cesarean section as mode of delivery.

  • Fetal Monitoring: Continuous fetal heart rate monitoring is commonly used during labor to assess the baby's well-being. If a fetal arrhythmia is known or suspected, healthcare providers may pay special attention to the baby's heart rate pattern during labor to ensure that it remains within a safe range.

  • Preparation for Possible Complications: In cases of known fetal arrhythmia, healthcare providers may prepare for potential complications that could arise during delivery, such as the need for immediate evaluation and intervention by pediatric cardiologists if the baby exhibits signs of distress.

  • Postnatal Assessment and Care: Babies born with fetal arrhythmias may require close monitoring in the immediate postnatal period to assess their heart rhythm and overall health. Pediatric cardiologists may be involved in evaluating and managing the baby's condition shortly after birth.

Related Programs