Arrhythmias Long QT Syndrome

What is long QT syndrome?

Long QT syndrome (LQTS) is a type of conduction disorder. A conduction disorder is a problem with the electrical system that controls your heartbeat.

The term “long QT” refers to a problem with the pattern seen on an electrocardiogram (EKG). An EKG is a test that detects and records your heart’s electrical activity. Information from the EKG is mapped on a graph so your doctor can study your heart’s electrical activity. Each heartbeat is mapped as five separate electrical waves: P, Q, R, S, and T.

The electrical activity that occurs between the Q and T waves is called the QT interval. This interval shows electrical activity in the heart’s lower chambers, called the ventricles. Normally the time between the Q wave and the T wave is about a third of each heartbeat cycle. However, in people who have LQTS, the QT interval lasts longer than normal.


The image shows the standard setup for an EKG. In Figure A, a normal heart rhythm recording shows the electrical pattern of a regular heartbeat. In Figure B, a patient lies in a bed with EKG electrodes attached to his chest, upper arms, and legs. A nurse monitors the painless procedure.
The image shows the standard setup for an EKG. In Figure A, a normal heart rhythm recording shows the electrical pattern of a regular heartbeat. In Figure B, a patient lies in a bed with EKG electrodes attached to his chest, upper arms, and legs. A nurse monitors the painless procedure.

A long QT interval can upset the careful timing of the heartbeat and cause sudden uncontrollable fast heart rhythms. LQTS is rare, and not everyone who has LQTS has dangerous heart rhythms. When they do occur, though, they can be fatal.

What causes long QT syndrome?

On the surface of each heart muscle cell are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium, and potassium atoms (ions) flow into and out of each cell. This generates the heart’s electrical activity. In people who have LQTS, the ion channels may not work well, or there may be too few of them. This may disrupt electrical activity in the heart’s lower chambers, or ventricles, and cause dangerous arrhythmias.

LQTS is often inherited , which means you are born with the condition and have it your whole life. You also can acquire LQTS. This means you are not born with the disorder but develop it during your lifetime.

The following factors can raise your risk of LQTS:

  • A family history of LQTS, or if someone in your family has had unexplained fainting or seizures, drowning or near drowning, or unexplained sudden death
  • Heart conditions such as cardiomyopathy and congenital heart defects
  • Medical conditions, such as eating disorders, thyroid disease, or serious diarrhea or vomiting, that cause low blood levels of potassium, magnesium, or calcium
  • Medicines that affect how your heart’s ion channels work, including some antibiotics, antidepressants, and antihistamines
  • Sex: LQTS is more common in women than men. Women who have LQTS are more likely to faint or die suddenly from the disorder during menstruation and shortly after giving birth.

What are the symptoms?

Some people who have LQTS may not have any symptoms. This is called silent LQTS. Others may have symptoms of arrhythmia. These symptoms may happen in specific situations, such as when you experience physical or emotional stress or when you sleep. The symptoms of inherited types of LQTS often start during childhood. It is rare to start having symptoms after 40 years of age.

Symptoms of LQTS may include:

  • Fainting, which may happen during physical or emotional stress, and may include fluttering feelings in your chest before fainting
  • Drowning or near drowning, which may be due to fainting while swimming
  • Noisy gasping while sleeping
  • Seizures

In about 1 out of 10 people who have LQTS, cardiac arrest (CA) or a sudden death is the first sign of LQTS. CA is a condition in which the heart suddenly stops beating for no obvious reason. People who have CA die within minutes unless they receive treatment.

Some types of LQTS are associated with problems in other parts of the body, such as deafness; muscle weakness; problems with the structure of your face, fingers, toes, and spine; and problems with behavior, learning, and memory.

How is it diagnosed?

If someone in your family has LQTS, your doctor may use heart tests and genetic testing to screen you for this condition. If you have an inherited type of LQTS, talk to your doctor and family members about possible genetic testing for your family members.

To diagnose long QT syndrome, your doctor will ask about your medical history, your family’s medical history, your symptoms, and what medicines you take. They will perform a physical exam and may order one or more tests:

  • Blood tests can check your electrolytes and thyroid hormones levels.
  • Genetic testing will look for changes in your genes that may cause LQTS and find out which type of LQTS you have.
  • Heart tests measure your heart’s electrical activity. An EKG is the most common test used to diagnose LQTS. Because your QT interval may change from time to time, you may need to have several EKGs over a period of days or weeks or use a Holter monitor. You may also need a stress test to measure your heart rhythm while your heart is working hard and beating fast.

How is it treated and managed?

The goal of treating LQTS is to prevent arrhythmias and fainting spells. Treatment isn’t a cure for the disorder and may not restore a normal QT interval. However, treatment greatly lowers the risk of life-threatening problems.

Treatment may include:

  • Lifestyle changes: Your doctor may ask you to avoid things that can cause problems with your heart rhythm, such as swimming and other vigorous physical activity, sudden loud noises such as an alarm clock, stressful situations, and some medicines. Ask your doctor about eating more potassium-rich foods (such as bananas) or taking potassium supplements daily.
  • Medicine: You may need beta blockers to prevent your heart from beating faster in response to physical or emotional stress. If you have low electrolyte ion levels, your doctor may give you magnesium or potassium through your veins.
  • Medical devices: Your doctor may recommend a device such as a pacemaker or implantable cardioverter defibrillator to help control your heart rhythm.
  • Surgery: You may need surgery to cut the nerves that cause dangerous heart rhythms. This keeps your heart beating at a steady pace and lowers the risk of arrhythmias caused by stress or exercise.

What happens if it is not treated?

LQTS is usually a lifelong condition. The risk of having an abnormal heart rhythm that leads to fainting or cardiac arrest may lessen as you get older, especially in men after age 40. However, the risk never completely goes away. In boys who have LQTS, the QT interval often returns to normal after puberty. If this happens, the risk of LQTS symptoms and complications goes down.

Visit the Living With Arrhythmias page to learn how to prevent complications and stay safe.

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