Long QT Syndrome

What is long QT syndrome?

Long QT syndrome (LQTS) is a problem with the heart’s electrical rhythm that can cause fast, irregular heartbeats (arrhythmias). It can be present at birth, but it may not be found until later in life.

Fast, irregular heartbeats can prevent your child’s body and brain from getting as much oxygen-rich blood as normal. If someone’s brain does not get enough oxygen, they can faint and could die without warning.

  • The heart has 4 chambers (spaces that hold blood): 2 atria at the top and 2 ventricles at the bottom. A complex electrical system makes these chambers squeeze and relax, at the right time and in the right order, to pump blood.

    A heartbeat starts in the right atrium when a group of cells (sinus node) sends an electrical signal. The signal travels from the atria to the ventricles, making the muscle walls squeeze. Then the muscle walls relax so they are ready for the next beat.

  • In LQTS, it takes longer than normal for the muscle walls to relax. By itself, this may not be a problem. But when this takes too long, the overall heartbeat can become fast and irregular.

    Children with LQTS can suddenly develop a fast heartbeat that keeps their heart from squeezing the way it should. This is more common if they are doing a strenuous activity, are excited or are startled.

  • Some children are born with LQTS because 1 or both of their parents passed down a gene that causes the condition. This is known as “inherited LQTS.” Parents may not even know they have LQTS because many people with LQTS have no symptoms.

    Some children and young adults get LQTS because they take medicines that make the heart take longer than normal to relax after it squeezes. This is called “acquired LQTS.” This may just be a side effect of the medicines, not something that they will have for their entire life.

Long QT Syndrome at Seattle Children’s

    • Seattle Children’s team of 40+ pediatric cardiologists diagnoses and treats long QT syndrome in children of all ages, from infants to adolescents.
    • Our Arrhythmia Program includes 3 full-time pediatric electrophysiologists, more than anywhere else in the region. After their training in pediatric cardiology, they have further subspecialty training in dealing with cardiac arrhythmias, including the life-threatening heart rhythms that can happen in children with LQTS. The Arrhythmia Program is also supported by a team of specialty technicians and nurses who know how to deal with these conditions.
    • We offer a full range of diagnostic procedures and treatments. Along with using heart medicines, we have deep experience implanting a pacemaker or defibrillator in children who need these devices to correct arrhythmias.
    • To help you understand your child’s condition – and the risk for other family members – our Cardiac Genetics Program combines the expertise of cardiologists, medical geneticists and genetic counselors.
    • If your child was born with LQTS, we have a special Adult Congenital Heart Disease Program to meet your child’s long-term healthcare needs. This program, shared with the University of Washington, transitions your child to adult care when they are ready.
    • We are committed to your child’s overall health and well-being and to helping your child live a full and active life.
    • Whatever types of care your child needs, we will help your family through this experience. We will discuss your child’s condition and treatment options in ways you understand and involve you in every decision.
    • Our nurses are experienced at supporting families with long QT syndrome. They help manage your child’s care, teach you and your child about LQTS, explain activity limits your child might need and connect you with other families living with this condition.
    • Our child life specialists know how to help children understand their illnesses and treatments in ways that make sense for their age.
    • Seattle Children’s has many resources, from financial to spiritual, to support your child and your family and make the journey as smooth as possible.
    • Read more about the supportive care we offer.
    • Doctors at Seattle Children’s are working to advance treatment for long QT syndrome and enhance the quality of life for children with this condition.
    • Dr. Jack Salerno has worked with organizations, like the Nick of Time Foundation, to help identify young people who might have LQTS or other arrhythmia conditions before they develop a problem.
    • Dr. Terrence Chun has trained and performed research in the molecular basis of LQTS, prenatal diagnosis and how to individualize care for different children and families. He has worked with our cardiac surgeons to develop new minimally invasive procedures to place pacemakers and defibrillators that other institutions have adopted.
    • Dr. Stephen Seslar has been part of projects to create large national databases of health information to better understand LQTS and other heart conditions in children.
    • Nurses in our Arrhythmia Program provide education for community and school nurses about LQTS and how they can help children with this condition thrive in school and other activities.

Symptoms of Long QT Syndrome

Children with LQTS usually do not have symptoms unless they develop an arrhythmia. If their heart begins beating too fast, they might faint because their brain is not getting enough blood.

Symptoms that happen with fainting may include:

  • Dizziness
  • Heart palpitations
  • Racing heart
  • Blurred vision

Sometimes a fainting spell is mistaken for a seizure or it seems like a response to stress. Fainting can also lead to drowning if it happens while your child is swimming.

Your child should see their healthcare provider if they faint, have a seizure or have a drowning incident and there is no clear reason or you already know they or another family member has LQTS.

In people with LQTS, the heart can suddenly stop beating, a condition called sudden cardiac arrest. In some cases, this is the first sign of LQTS. Sudden cardiac arrest usually causes death. However, some children who receive treatment quickly, within minutes, can survive.

Diagnosing Long QT Syndrome

To diagnose this condition, your child’s doctor will examine your child and use a stethoscope to listen to their heart. The doctor will ask about any symptoms your child has, their health history and your family health history. They will want your child to have an electrocardiogram (ECG) and possibly other tests.


Your child will have an ECG test to record the electrical signal in your child’s heart and check the pattern. Doctors name the parts of this pattern with the letters P, Q, R, S and T.

The “QT interval” is the time from when the ventricles start to squeeze until they are relaxed and ready to squeeze again. If this takes longer than normal, it is called a “prolonged QT interval.” A child with a prolonged QT interval may have LQTS.

Holter monitor

An ECG will not always detect LQTS because some children do not have a prolonged QT interval all of the time. To get enough information about the electrical signal in your child’s heart, your child may need to wear a portable ECG device called a Holter monitor. This device can record their heart’s activity for 24 hours.

Exercise Test

Your child may also need an exercise test. This means we monitor their heart rate and rhythm while they exercise.

Genetic Testing

The doctor may suggest genetic testing to see if genes play a role in your child’s condition. If they do, then others in the family may need testing to see if they are affected.

Treating Long QT Syndrome

The goal of treatment for LQTS is to prevent your child’s heart from having dangerous arrhythmias. Treatment does not cure LQTS.


LQTS can be treated with medicines, like beta-blockers. These slow the heart rate and decrease the chance of having dangerous arrhythmias and sudden cardiac arrest.

Implanted Devices

Some children with LQTS need a pacemaker to help control the speed and pattern of their heartbeat or a defibrillator to bring the heart back to a normal rhythm. Read more about these devices in our Arrhythmia Program.

Avoiding Triggers

Your child’s doctor may also want your child to avoid things that might trigger an arrhythmia. Common triggers include: 

  • Strenuous exercise
  • Certain medicines
  • Conditions that can lower your child’s level of the mineral potassium (like diarrhea and vomiting)
  • Loud noises that might startle them during sleep 

Triggers can be different for your child than for other children, so talk with your child’s doctor about this.

Contact Us 

Contact the Heart Center at 206-987-2515 to request an appointment, a second opinion or more information.

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