Long QT Syndrome

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 cause an arrhythmia, or abnormal heart rhythm, which 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.

Causes of LQTS

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.

Signs and symptoms of Long QT Syndrome

LQTS can cause:

  • Fainting, especially as a result of acute emotions (such as anger or surprise), exercise, menses (menstruation), or swimming in cold water
  • Seizures
  • Ventricular arrhythmias (abnormal heart rhythms originating in the lower chambers)
  • Sudden cardiac arrest

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

Testing and diagnosis of LQTS

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 your 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.

Treatment for Long QT Syndrome

People with LQTS may have to:

  • Take medications called beta blockers
  • Avoid triggers that may cause an arrhythmia event
  • Avoid medications that can prolong the QT interval

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:

  • LQT1: Individuals with LQT1 are more likely to have symptoms with exercise, although symptoms can occur with emotional stress and even when resting. It can be treated effectively with beta blocker medication in most patients. It is important for individuals with LQT1 to maintain normal potassium levels and lifestyle modifications in addition to taking their medications.
  • LQT2: Individuals with LQT2 are more likely to have symptoms with emotional stress, but symptoms can also occur during exercise and when resting. LQT2 can be treated moderately well with beta blocker medication, but treatment may be improved by also maintaining a good potassium level. Of the three major LQTS types, LQT2 is most affected by medications that further prolong the QT interval.
  • LQT3: Individuals with LQT3 are more likely to have symptoms during rest. LQT3 is less well treated with beta blocker medication than other types of LQTS, but beta blocker medication is still effective in many of these patients. LQT3 patients with symptoms may need to take another medication in addition to beta blockers. Some patients may need an implantable cardioverter-defibrillator (ICD).

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).

Outlook for LQTS

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

Follow-up care for LQTS

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 lifelong 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.

Reviewed by V. Ramesh Iyer, MD, MRCP

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