Long QT syndrome (LQTS) is a heart rhythm disorder in children that affects how the heart beats. It involves a problem with the heart’s electrical system.
In LQTS, the heart’s two lower chambers (ventricles) take longer than normal to reset between beats.
The “QT interval” is a measurement on an electrocardiogram (EKG). It shows how long the heart’s lower chambers take to reset after each beat.
When the QT interval is too long, it is called a prolonged QT interval. It is also sometimes called a prolonged QTc interval—the “c” stands for “corrected.” This can lead to fast or irregular heart rhythms. These rhythms may cause fainting or, in rare cases, sudden cardiac arrest.
There are two main types of long QT syndrome:
Symptoms can vary widely. Some children have mild or no symptoms. Others may need ongoing care.
The heart beats using small electrical signals. Special parts of heart cells, called ion channels, help control this process. Ion channels act like electrical gates. They open and close to allow charged particles to rush in and out of heart cells. This movement creates electrical signals.
These signals travel through the heart in a set pattern. The signal starts in the right upper chamber, moves to the left upper chamber, then travels down to the lower chambers. This pattern keeps the heartbeat steady and regular.
The QT interval on an EKG reflects the time it takes for the heart’s lower chambers to contract and reset.
Proper timing is very important. If signals are too slow or uneven, the heart rhythm can become unsafe. When this system does not work as it should, LQTS can occur.
In LQTS, the reset time is longer than normal. This delay can lead to fast or irregular heart rhythms. One type of abnormal rhythm is called Torsades de Pointes (TdP).
These rhythm problems may reduce blood flow to the brain. This can cause fainting, seizures or sudden cardiac arrest.
Common triggers include:
Many cases are caused by changes in genes that affect the heart’s electrical system. LQTS can run in families. A parent may pass the condition to their child.
There are different types of LQTS caused by different genetic changes. There are many subtypes, but the most common are:
Other causes include:
These are known as acquired causes of long QT syndrome.
Many children with LQTS have no symptoms. Others may have symptoms such as:
These symptoms often happen during triggers like exercise or stress.
In severe cases, LQTS can cause sudden cardiac arrest. Any fainting episode linked to activity or strong emotion should be checked right away.
Doctors often start with an electrocardiogram (EKG). This test measures the QT interval and can show if it is too long. An EKG records the heart’s electrical signals using sensors on the chest, arms and legs.
Other tests may include:
Doctors may also do tests to rule out other causes of abnormal heart rhythms. Sometimes, testing must be repeated to confirm the diagnosis.
Treatment depends on the child’s symptoms and risk level. The goal is to prevent fainting, seizures or sudden cardiac death by managing abnormal heart rhythm problems.
Treatment options may include:
Keeping electrolytes balanced is important. This may include eating foods high in potassium and magnesium or taking supplements if needed. Some examples of foods rich in magnesium and / or potassium include leafy green vegetables, nuts, seeds, legumes, and certain fish.
With the right support, many children with LQTS can live active lives. Patients should avoid known triggers, follow guidance on sports and activity, and take medicines as prescribed.
Schools should have an emergency plan. Access to an automated external defibrillator (AED) can save a life.
Family members should also have testing for long QT syndrome when there is a genetic cause.
Children with LQTS need regular follow-up care. Doctors will monitor their heart rhythm and adjust treatment as they grow.
Because this condition is often lifelong, ongoing management helps reduce risks and keep children safe.
Many children with LQTS do well over time. Treatment and lifestyle changes can lower the risk of serious events.
Early diagnosis also plays an important role in preventing complications and improving outcomes. As children grow, they will transition to adult heart rhythm care.
It can be serious, but treatment greatly lowers the risk.
There is no cure for inherited LQTS. However, it can be managed well.
Some can, with guidance from their care team. Activity plans are individualized.
Yes. LQTS often runs in families, so testing is important.
Visits vary by child. Many need regular, ongoing monitoring.
A heart affected by congenital heart disease is unique. For that reason, adult congenital heart surgery outcomes are superior at a children’s hospital. Our experts are here to help.
Last Updated 08/2026
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