Long QT Syndrome

What is long QT syndrome?

Long QT syndrome (LQTS) is a disorder of the heart’s electrical rhythm that can cause fast and irregular heartbeats (arrhythmia). It can be present at birth, but may not be detected until later in life. LQTS is rare and affects children and young adults.

There are 4 chambers in the heart: the top 2 are the atria and the lower 2 are the ventricles. The heart uses a complex electrical system to make the muscle walls of the atria and ventricles work together to pump blood.

A heartbeat is the squeezing and relaxing of the muscle walls at the right times and in the right order. The heartbeat starts in the right atrium. When a group of cells called the sinus node sends an electrical signal, the heartbeat is initiated. This is known as the heart’s pacemaker.

The signal travels on nerve-like fibers from the atria to the ventricles and causes the muscle to squeeze at the right time. The muscle then relaxes so that it is ready for the next beat. In children with LQTS, the relaxation phase takes longer than normal, making the heartbeat more likely to be fast and irregular.

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

Fast and irregular heartbeats can prevent the body and brain from getting as much oxygen-rich (red) blood as normal. If someone’s brain doesn’t get enough oxygen, they can faint and could die without warning.

  • Some children are born with LQTS because one or both of their parents passed down a gene that causes the condition. This is known as “inherited LQTS.” Parents may not know they have the gene and LQTS themselves because many people with LQTS have no symptoms. At least 12 genes have been associated with LQTS.

    Some children and young adults get LQTS because they take medicines that make the relaxation phase of the heartbeat longer than normal. This is called “acquired LQTS.”

    LQTS is rare; about 1 in every 7,000 people has it.

Long QT Syndrome at Seattle Children’s


  • Our Heart Center is the top-ranked cardiology and cardiac surgery program in the Northwest and among the best in the nation, according to U.S. News & World Report. With more than 40 pediatric cardiologists, we have experience diagnosing and treating every kind of heart problem.

    Our heart team has treated many children and young adults with LQTS. We have extensive experience with the treatment these patients may require.

    Seattle Children’s has been treating children since 1907. Our team members are trained in their fields and in meeting the unique needs of children. For example, the doctors who give your child anesthesia (sedation) are board certified in pediatric anesthesiology. This means they have extra years of training in how to take care of kids. Our child life specialists know how to help children understand their illnesses and treatments in ways that make sense for their age.

  • When you come to Seattle Children’s, a team of people will take care of your child. Along with your child’s heart doctor (cardiologist), you are connected with newborn specialists (neonatologists), lung doctors (pulmonologists), nurses, child life specialists, social workers and others, if their expertise is needed.

    We’re committed to your child’s overall health and well-being. We’ll help your family through this experience and discuss treatments in ways you can understand and involve you in every decision.

    Read more about the supportive care we offer.

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 isn’t getting enough blood. Symptoms that occur with fainting may include dizziness, heart palpitations, racing heart and blurred vision.

Sometimes a fainting spell is mistaken for a seizure or it seems like a response to stress. In other cases, a child drowns because they fainted while swimming.

Your child should be seen by their healthcare provider if they faint, have a seizure or nearly drown and there’s no clear reason. They should also be checked if you already know they have LQTS or if there are other family members with the condition.

The heart of someone with LQTS can suddenly stop beating, a condition called sudden cardiac arrest. This may be 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 doctor will examine your child and use a stethoscope to listen to their heart. The doctor will ask for details about any symptoms your child has, their health history and your family health history.

Your child will also have an electrocardiogram (ECG) test to tell doctors information about how your child’s heart works.

Using an ECG, a healthcare provider can examine the electrical signal in your child’s heart. The signal produces a pattern. Providers name different parts of the patterns with the letters P, Q, R, S and T. The time from when the ventricles start to squeeze until they are relaxed and ready to squeeze again is the “QT interval.”

A provider can measure this time and know if it takes longer than normal. If it takes longer, it’s called a “prolonged QT interval.” A child with a prolonged QT interval may have LQTS.

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.

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

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

Treating Long QT Syndrome

The goal of treatment for LQTS is to prevent your child’s heart from having dangerous irregular and fast heartbeats (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 heart rhythms and sudden cardiac arrest by blunting the heart’s reaction to adrenaline.

Some children with LQTS may need a pacemaker or a defibrillator. Read more about these devices and our Arrhythmia Program.

Your 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 potassium (like diarrhea and vomiting)
  • Loud noises that might startle them during sleep 

What triggers your child can be different from other children, so talk with your doctor about it.

Contact Us 

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

Providers, see how to refer a patient.