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Most children do not have any symptoms of long QT syndrome. You may only become aware of your child’s condition because of a doctor’s visit or medical test, genetic testing results, or if you have a family history of the syndrome.

Symptoms of long QT syndrome usually happen when a child is startled, and the most common symptoms include seizures and fainting.

Symptoms can also happen while your child sleeps, or if they are woken up suddenly. Although not common, sometimes the heart can beat so fast or unpredictably that it can cause sudden death.

When to See a Doctor

It is important to catch and treat your child’s long QT syndrome as early as you can. It is easily controlled with treatment but can be fatal if not treated, so seek treatment as soon as possible. Make an appointment to see your child’s doctor if you notice any of the symptoms of long QT syndrome.


There are a few different causes of long QT syndrome. Most children with long QT syndrome are born with it, but it can also develop because of some medicines, salt and mineral imbalances in the body, or other medical conditions.

Diagnosis and Tests

Your child’s doctor will ask you for a review of any symptoms your child may have, including how long they have had them and how severe they are. Your child’s doctor will also conduct a physical exam. If your doctor thinks your child may have long QT syndrome, they will order more tests to help confirm the diagnosis.

These other tests may include:

  • An EKG, which is a test that monitors the timing of the heartbeat
  • A Holter monitor, which is a mobile EKG device that is worn for at least a day
  • An event monitor, which is a portable EKG device that is worn for a few weeks

Although not common, sometimes an EKG does not show the long QT interval, and makes it hard to confirm the diagnosis. If this is the case, your doctor may order other tests, such as:

  • Genetic testing, which helps your doctor see if your child has genetic causes for the syndrome
  • Exercise stress test, which is where an EKG is done while your child is walking or running on a treadmill to help the heart beat more
  • A non-exercise stress test, which is where an EKG is performed right after a child is given medicine to help the heart beat faster, like they are playing hard

You may want to seek a second opinion if your child is diagnosed with long QT syndrome.


Treatment for long QT syndrome will depend on your child’s symptoms.

The goal of long QT syndrome treatment is to prevent sudden death by keeping the heart from beating too fast or out of control. Your child’s doctor may also treat heart rhythm disorders as needed.

Treatment may include one or more of the following:

  • Lifestyle changes
  • Medicine
  • Surgery
  • Implanted medical devices.

Talk to your child’s doctor to figure out the best treatment plan for your child. If your child has long QT syndrome:

  • Talk to your child’s doctor before starting any medicines to make sure you avoid ones that may cause the QT cycle to be longer.
  • If your child has a fever, contact your child’s doctor. Your child should not run a fever for a long period of time.
  • Make sure your child stays hydrated, especially during times where they are sick and may have a higher chance of getting dehydrated (such as when they are throwing up or have diarrhea).
  • Try to prevent your child from getting startled or scared, or avoid situations that may cause them to get too excited or angry.
  • Don’t allow your child to participate in strenuous sports or exercise
  • Work with your doctor to create a plan just in case your child does have a cardiac event.


Because your child may develop long QT syndrome before birth, there may be nothing you can do to prevent it.

Keep salt and mineral levels within a healthy range to help prevent this syndrome from developing.

If your child has long QT syndrome, follow the doctor’s plan to help prevent problems, and make sure to have a plan in case a cardiac event does happen.

What is Long QT Syndrome?

Long QT syndrome is a rare heart disorder that can sometimes cause rapid, uncontrollable heartbeats. This heartbeat pattern can cause your child to all of a sudden faint or have a seizure.

The term “long QT” is in reference to the activity in the heart’s lower chambers as measured with an electrocardiogram [ee-lek-troh-CAR-dee-oh-gram] (EKG or ECG). This measurement is called the QT interval. Most of the time, the QT interval takes about one-third of each heartbeat cycle. In children that have long QT syndrome, this part of the heartbeat lasts longer than normal. It causes rapid or abnormal heartbeats by throwing off the rest of the heartbeat cycle. Children with this disorder may not have symptoms for a while. Although there is no cure, there are treatments that can help reduce or prevent symptoms.