Cardiac Center

Long QT Syndrome

Before you begin reading about Long QT Syndrome, please read the explanation of how the normal heart works for a basic understanding of its structure and function.

What is Long QT Syndrome?

Long QT Syndrome (LQTS) is a medical condition resulting from an abnormality in the electrical system of the heart.

The “QT” interval refers to a specific measurement on the electrocardiogram, the record of the electrical activity of a person’s heart. A “QT” interval is measured in seconds or in milliseconds. “Long QT” means the QT interval lasts longer than normal.

A prolonged QT interval occurs when the cells of the ventricles (the lower chambers of the heart) don’t electrically reset at the same time or take longer than normal to reset. This can allow for an arrhythmia, or abnormal heart rhythm, to occur that can be potentially lethal. However, there are some QT intervals that are at the borderline duration that still may be considered normal. A person has LQTS when there is abnormal prolongation of the QT interval that can cause certain symptoms, such as fainting.

In most cases LQTS is inherited, or caused by a genetic mutation that is passed down through a family. It can also be caused by certain medications. LQTS can manifest in different forms and can be difficult to diagnose.

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What are the symptoms of Long QT Syndrome?

LQTS can cause:

Sometimes children or adults have no symptoms until they experience sudden cardiac arrest. At the same rate, not all patients who have fainting have LQTS.

Children’s Hospital has a program called Youth Heart Watch that aims to raise awareness of the risk of sudden cardiac arrest in children, and helps to ensure that all schools in Pennsylvania, New Jersey and Delaware have life-saving devices called automated external defibrillators (AEDs).

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How is of Long QT Syndrome diagnosed?

If a child has repeated fainting episodes, or other symptoms, a pediatrician may refer him or her to a pediatric cardiologist. It is not unusual for individuals with LQTS to have no symptoms until the teenage or early adult years.

LQTS is diagnosed with an electrocardiogram. Evaluation often includes a Holter monitor and exercise stress testing.

Because the condition is usually inherited, your cardiologist may consider genetic testing and counseling. If a child has LQTS, brothers, sisters, parents and other family members may also have it. Your cardiologist at The Children’s Hospital of Philadelphia will talk to you about these risks and discuss steps to address them, including testing the entire family for LQTS.

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What are the treatment options for Long QT Syndrome?

If a person has LQTS and isn’t treated, the risk of sudden death over a lifetime is high.

A person with LQTS may have to:

Beta blockers significantly reduce the incidence of arrhythmias and sudden cardiac arrest. In some cases, however, an implantable cardioverter-defibrillator (ICD), a special pacemaker that can interrupt arrhythmias, is necessary to stop these arrhythmias. Implanting this device requires surgery.

Some children with LQTS have to limit competitive sports and other exercise. It is particularly dangerous for a person with LQTS to have low levels of electrolytes (sodium and potassium are two examples of electrolytes). Remaining hydrated by drinking water or sports drinks (which contain electrolytes) is important, particularly before, during and after exercise.

Treatment may depend on which type of LQTS your child has. The three major types of LQTS are:

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What kind of follow-up care is required for Long QT Syndrome?

Your child won’t outgrow LQTS. He or she will have to continue to take beta blockers, or continue other appropriate treatment, and will require life-long care by a cardiologist. In most cases, an annual checkup will be sufficient.

Most children and adults with LQTS lead healthy, normal lives. It is very important that they and their families be aware of the signs of sudden cardiac arrest, so that they can get help immediately if needed.

The Children’s Hospital of Philadelphia has one of the leading teams in the diagnosis and care of LQTS in children, adolescents and young adults.

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Contact the Cardiac Center at The Children's Hospital of Philadelphia for a second opinion or for more information.

Reviewed by: V. Ramesh Iyer, MD, MRCP
Date: June 2013

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