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Tachyarrhythmia

09/06/2023 Conditions

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What is tachyarrhythmia?

Fetal tachyarrhythmia is an abnormally fast fetal heart rate.

In some cases the fast heartbeat may also have an irregular rhythm.

Tachyarrhythmia is one of several types of fetal cardiac arrhythmias, congenital heart conditions involving an abnormal heartbeat.

The condition is also sometimes referred to as tachycardia.

How does tachyarrhythmia affect my baby?

By 16 weeks of pregnancy, the fetus’ heart is normally completely formed and  beats at a rate of 110 to 160 beats per minute (bpm).

Fetal tachyarrhythmia is generally defined as a heart rate that exceeds 180 to 200 beats per minute.

In most cases, if the increased fetal heart rate occurs only intermittently, or if it can be controlled with medication during pregnancy, the prognosis is good.

In rare cases, a sustained fast heart rate can lead to fetal heart failure or non-immune hydrops, a life-threatening condition where fluid accumulates in multiple areas of the baby’s body, causing severe swelling. Outcomes in these cases are poor.  

Types of Tachyarrhythmia

There are several types of tachyarrhythmia ranging from mild to serious, including:

  • Sinus tachycardia (ST) – In this condition, the fetal heart rate is above 180 bpm but usually less than 200 bpm, with normal conduction (the electrical signal transmits normally from the upper chambers to the lower chambers). Sinus tachycardia may be brief, due to fetal activity, or it may be persistent and caused by other maternal or fetal conditions, such as maternal hyperthyroidism, intrauterine infections, fetal anemia and fetal hypoxia (lack of oxygen)
  • Supraventricular tachycardia (SVT) – This is the most common form of fetal tachyarrhythmia. It occurs when both the atria and ventricles are beating greater than 220 bpm. SVT is typically caused by problems with the heart’s electrical system, which sends the electrical impulses that cause the heart muscles to contract, forming your heartbeat.
  • Atrial flutter (AFL) – In atrial flutter, the atria beat significantly faster than the ventricles. If this irregular heart rhythm is sustained, it places the fetus at increased risk of hydrops. AFL may be associated with congenital heart disease or chromosomal abnormalities.
  • Ventricular tachycardia (VT) – In this rare condition, the fetus’ ventricular heartbeat is faster than the atrial rate. VT may be associated with myocarditis (inflammation of the heart muscle), complete heart block, or congenital long QT syndrome (a rhythm disorder that can cause fast, chaotic heartbeats).

Cause and Prevalence

Fetal tachyarrhythmia is estimated to occur in less than 1% of all pregnancies.

Maternal and fetal conditions that can increase the risk of tachyarrhythmia include:

Mother

  • Hyperthyroidism
  • Fever associated with infections
  • Substance abuse
  • Certain medications

Fetus

Diagnosis

Fetal tachyarrhythmia is typically diagnosed during a routine prenatal ultrasound or when the doctor listens to the fetal heartbeat.

In some cases, rhythm abnormalities may not start until later in pregnancy. Generally, the mother has no symptoms and notices no change in fetal movement.

If an abnormally fast heartbeat is diagnosed, blood and urine tests may be run to screen for underlying maternal conditions that may be causing the fetal condition. Amniotic fluid levels will also be measured to determine if there is excess amniotic fluid, or polyhydramnios, a possible sign of fetal hydrops.

Prompt referral to a fetal cardiac center is vital for accurate, thorough diagnosis of the type of tachyarrhythmia and any related conditions, ensuring proper treatment. At Texas Children’s Fetal Center, we arrange for you to visit as quickly as possible for a comprehensive assessment by a team of specialists experienced in the full range of fetal cardiac arrhythmias, including maternal-fetal medicine (MFM) physicians (OB/GYNs specializing in high-risk pregnancies), fetal and pediatric cardiologists, fetal imaging experts, neonatologists, and pediatric electrophysiologists, specialists in heart rhythm problems.

Additional testing may include:

  • High-resolution anatomy ultrasound to confirm the diagnosis, evaluate the condition and look for other abnormalities or complications
  • Ultra-fast MRI for a more detailed view of fetal anatomy
  • Fetal echocardiogram to evaluate your baby’s heart structure and function and identify the type of arrhythmia
  • Doppler ultrasound to evaluate fetal blood flow
  • Amniocentesis and chromosomal analysis to screen for genetic abnormalities

Our specialists will then meet with you about the results, discuss treatment recommendations, and answer any questions your family has, to help you make the most informed decisions regarding your baby’s care and treatment.  

Treatment During Pregnancy

Treatment during pregnancy will depend on the type of tachyarrhythmia, gestational age of the baby, any associated conditions, and if there are signs of hydrops.

When treatment is required, the goal is to control the speed of the fetal heart rate and prevent the development of hydrops, enabling delivery at term. 

Treatment strategies include:

  • Close monitoring only. In cases involving intermittent tachycardia, treatment is typically not required, but the baby’s heart rate and well-being should be closely monitored until the condition completely resolves on its own.
  • Close management with medication to restore heart rate and rhythm by terminating the tachycardia (or controlling the ventricular rate by limiting conduction from upper chambers to lower chambers). The medication is given to the mother and passes through the placenta, an approach known as transplacental administration or therapy.
  • Treatment to address any underlying causes
  • Premature or emergency delivery, when needed

Delivery

Delivery should take place at a center with the highest quality congenital heart program, ensuring the expertise and resources required to treat fetal arrhythmias during delivery and after birth, including an advanced neonatal or cardiac intensive care unit (NICU or CICU), if needed.

Delivery and postnatal care should be carefully planned and coordinated across a team of maternal-fetal medicine specialists, cardiologists and neonatologists experienced in these rare conditions. In some cases, a caesarean delivery may be advised.

Our Fetal Center team works closely with the pediatric experts at Texas Children’s Heart Center for seamless access to the critical care services and specialists your child may need after delivery, avoiding the need for transfers. Here, the pediatric cardiologists treating your baby have been an integral part of their care team since before birth.

Treatment After Birth

Treatment needs after birth vary based on the type and severity of the baby’s tachyarrhythmia.

In some cases, the heart rate may slow down to a normal rate over time, without intervention. Babies should be followed closely by a pediatric cardiologist experience in congenital heart conditions until the condition is completely resolved.

In other cases, medication may be given to the infant following birth to treat the underlying arrhythmia.

Your baby’s postnatal care team may include:

Why Texas Children’s Fetal Center?

  • A single location for expert maternal, fetal and pediatric care. At Texas Children’s Hospital, mothers and babies receive the specialized care required for the diagnosis and treatment of congenital heart conditions all in one location, for highly coordinated care and treatment planning.
  • A skilled, experienced team with proven outcomes. We have a dedicated team of maternal-fetal medicine specialists, fetal imaging experts, cardiologists, neonatologists, electrophysiologists and others who work in concert to care for you and your baby every step of the way, using proven protocols we’ve developed over the years. With their combined expertise and unified approach, this team offers the best possible care for pregnancies involving fetal arrhythmias.
  • We care for your child’s needs at every stage of life. Our comprehensive approach starts with your first prenatal visit and continues through delivery, postnatal care, childhood and beyond, as needed, thanks to one of the nation’s leading teams of fetal and pediatric heart specialists.

Texas Children’s Hospital – #1 in the Nation for Pediatric Cardiology and Heart Surgery

Our Fetal Cardiology Program is a collaboration between Texas Children’s Fetal Center and Texas Children’s Heart Center, ranked #1 in the nation for pediatric cardiology and heart surgery by U.S. News & World Report for consecutive years, with outcomes among the best in the country.

In the News

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Research and Clinical Trials

Texas Children’s, together with our partner institution Baylor College of Medicine, constantly strives to seek new and better treatments for babies with congenital heart conditions.

For more information, please contact the Cardiovascular Clinical Research Core at 832-826-2064 or email sandrea@texaschildrens.org.

Learn more about our fetal cardiology research.