Learn more about heart conditions in babies.

The birth of your baby is exciting but can create worry at times. Sometimes babies experience an abnormal heart rhythm, called an arrhythmia. One of the more common arrhythmias in babies is supraventricular tachycardia (SVT).

SVT in infants is a condition that causes a rapid heartbeat, or tachycardia. Although it’s concerning when anything is wrong with your infant, SVT is not often dangerous.

While it’s rarely life-threatening, SVT can cause some symptoms, so it’s always good to have your child seen by a cardiologist.

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What Is SVT?

SVT is the most common type of arrhythmia in children, affecting about one in every 1,000 children. An extra electrical pathway in the heart causes the fast heart rate.

The heart has four chambers: two upper chambers (called atria) and two lower chambers (called ventricles). Blood returning from the body first enters the right atrium, which squeezes blood into the right ventricle. Then it pauses to allow the ventricle to pump blood to the lungs. Oxygen-rich blood returns to the left atrium, gets pushed into the left ventricle, and then pumped back to the body.

The sinus node is a specialized structure in the right atrium that controls the normal heart rate by releasing electrical pulses. These pulses travel across the heart and control when the muscle squeezes or pumps. Electrical signals usually travel along one path from the upper to the lower chambers. In SVT, the child has an extra pathway for the signal to follow. The signal travels down the normal pathway and then back up the extra one allowing the electricity to get stuck going in a loop. The signal then travels around and around, rather than one-way, and causes the heart to beat faster.

Infants with SVT have heart rates of more than 180 beats per minute — and as high as 300 beats per minute. A normal heart rate for children younger than a year is between 100 and 180 beats per minute when calm.

What Causes SVT in Infants?

Children with SVT are born with an extra electrical pathway, most commonly separate from the normal conduction system.

Some children have an extra electrical connection coming from the normal conduction system. Being born with an extra electrical connection cannot be caused or prevented during pregnancy. Sometimes evidence of an extra pathway can be seen on an electrocardiogram (ECG), which is test that shows an electrical tracing of the heart activity. Pathways that can be seen on an ECG are called Wolff-Parkison-White syndrome, though most children with SVT have normal ECGs. SVT does not commonly run in families, though is a common diagnosis so can be seen in multiple family members.

Rarely, SVT occurs because the child has another heart issue at birth. A pediatric cardiologist will look for possible causes and any congenital heart defects. Most infants with SVT have an otherwise normal heart.

How Does SVT Affect Infants?

Usually, the fast heart rate doesn’t continue all the time. Most commonly, the child has an episode where the heart rate suddenly speeds up, leading to visible signs. These episodes can last a few seconds or hours up to several days.

In infants, signs of an episode include poor feeding, fast breathing, paleness, vomiting, or being more sleepy than usual. This is because the heart is working extra hard to keep up with the fast heart rate.

Most children will grow out of the condition by a year old. However, approximately 1 in 3 will have it happen again during school-age years, beginning around 5 years old and extending into the teenage years.

If your baby is having episodes of fast heartbeats, particularly when calm, you should see a cardiologist. A children’s heart specialist can do tests to diagnose SVT and guide its treatment.

SVT often happens off and on, so your child may have a normal heart rate while at the doctor’s office. Your doctor may send you home with a monitor to record your child’s heart rate for a couple days. Your doctor may also order an echocardiogram, or ultrasound evaluation of the heart, to see the structure and function of the heart.

What Is the Long-term Outlook for Children with SVT?

Overall, children with SVT lead healthy lives. In most cases, infants with SVT don’t have life-threatening complications or need invasive treatment, though they may need medication. With specialized care, your doctor can help you manage your baby’s condition. Your doctor may teach you how to take your baby’s pulse to monitor their heart rate.

Children with SVT may experience dizziness, shortness of breath, and fluttering in the chest. If your child has symptoms as they grow up, a doctor may teach them to do a vagal maneuver. This stimulates the vagus nerve, which tells the heart to slow down. Even when SVT occurs in infancy, most children can still participate fully in sports and other activities as they grow. Your child may need to regularly see a doctor or cardiologist for periodic monitoring of their heart.

Treatment for SVT in Infants

When needed, treatment for SVT in infants most often involves monitoring the heart rate and medication. A beta blocker is a type of medicine that helps prevent the heart from beating too fast.

If medication doesn’t help or SVT continues into childhood, your doctor may recommend an ablation. During this procedure, a thin tube, called a catheter, is inserted into a vein and threads it to the heart. The doctor uses heat or cold to destroy the extra tissue connection that’s causing the problem. Ablation is highly effective and carries low risks. Usually, ablation is reserved for children who continue to have episodes during their school-age or teenage years.

Having a specialized care team gives you the support you need. The Electrophysiology Program at the UPMC Children’s Hospital of Pittsburgh provides the latest testing and management for heart rhythm issues.

The program brings together children’s heart experts, diagnostic tests, and interventions to develop a plan for your family. The care team is here for you as your child grows as well to keep their heart healthy.

UptoDate, Heart rates in normal children, Link

MedLine Plus, Wolff-Parkinson-White syndrome, Link

Great Ormond Street Hospital for Children, Neonatal supraventricular tachycardia, Link

About UPMC

Headquartered in Pittsburgh, UPMC is a world-renowned health care provider and insurer. We operate 40 hospitals and 800 doctors’ offices and outpatient centers, with locations throughout Pennsylvania, Maryland, New York, West Virginia, and internationally. We employ 4,900 physicians, and we are leaders in clinical care, groundbreaking research, and treatment breakthroughs. U.S. News & World Report consistently ranks UPMC Presbyterian Shadyside as one of the nation’s best hospitals in many specialties and ranks UPMC Children’s Hospital of Pittsburgh on its Honor Roll of America’s Best Children’s Hospitals. We are dedicated to providing Life Changing Medicine to our communities.