What is long QT syndrome (LQTS)?

  • Long Q-T syndrome is a disorder of the heart’s electrical system.
  • The electrical activity of the heart is produced by the flow of ions (electrically charged particles of sodium, calcium, potassium, and chloride) in and out of the cells of the heart. Tiny ion channels control this flow.
  • The Q-T interval is the section on the electrocardiogram (ECG) - that represents the time it takes for the electrical system to fire an impulse through the ventricles and then recharge. It is translated to the time it takes for the heart muscle to contract and then recover.
  • LQTS occurs as the result of a defect in the ion channels, causing a delay in the time it takes for the electrical system to recharge after each heartbeat. When the Q-T interval is longer than normal, it increases the risk for torsade de pointes, a life-threatening form of ventricular tachycardia.
  • LQTS is rare. The prevalence is about 1 in 5,000 persons in the United States.

What causes LQTS?

Long Q-T syndrome can be acquired or congenital:

Acquired LQTS is caused by many medications. Sensitivity to these medications may be related to genetic causes.

Congenital LQTS is usually inherited. It is caused by an abnormality in the gene code for the ion channels. The abnormality of the ion channels slows the recovery phase of the heartbeat. Forms of inherited LQTS include:

  • Recent Classifications – Multiple ion channel abnormalities have been discovered. The most common ones include LQT1, LQT2, LQT3, LQT4, LQT5; these are classified by the type of channel which causes the LQTS. The type of LQTS classification is related to the risk of future cardiac events, those with LQT3 having the highest risk of life-threatening arrhythmias.
  • Jervell, Lange-Nielsen Syndrome (autosomal recessive inheritance pattern) – Both parents are carriers of the abnormal gene, but they may not manifest LQTS. Each child has a 25-percent chance of inheriting LQTS. This syndrome is associated with deafness at birth and is extremely rare, as there is a small chance that both parents would carry the LQTS gene.
  • Romano-Ward Syndrome (autosomal dominant inheritance pattern**) **– One parent has LQTS and the other parent usually does not. Each child has a 50-percent chance of inheriting the abnormal gene. In this syndrome, hearing is normal; however the likelihood that children in this family would have LQTS is greater. The gene may be present in all the couple’s children, some of them or none at all.

Those at risk for LQTS include:

  • Children who are deaf at birth
  • Children and young adults who have unexplained sudden death or syncope in family members
  • Blood relatives of family members with LQTS
  • Those with LQTS taking medications that can further prolong the QT intervals. See medications to avoid under Treatment Options.

Do you need to be screened for long QT syndrome?

Long QT Syndrome is a medical condition that can be passed on from generation to generation. It is important for you to be screened for this condition if you have a first-degree relative with Long QT Syndrome. First-degree relatives are your parents, siblings and children.

The first step is to tell your doctor that you have a family history of this condition. He or she may want to do diagnostic tests to check your heart. If these tests are positive, you should be seen by a cardiologist who is familiar with this condition.

What are the symptoms of long QT syndrome?

The most common symptoms include:

  • Syncope (fainting)
  • Seizures
  • Sudden death

The symptoms of LQTS are related to torsade de pointes. During this arrhythmia, the ventricle beats very fast and irregularly. The heart is unable to pump blood effectively to the body. If the brain does not receive an adequate blood supply, syncope (fainting) and seizure-like activity can occur. If the arrhythmia continues, sudden death will occur. If the heart rhythm returns to normal, symptoms will stop.

Symptoms are most common during:

  • Exercise (or within a few minutes after)
  • Emotional excitement, especially being startled
  • During sleep or upon waking suddenly

Some people with congenital LQTS never have symptoms. The diagnosis is made during a routine ECG or during an evaluation because a family member has it. Symptoms usually first appear during the early teen years.

How is LQTS diagnosed?

LQTS is usually diagnosed by measuring the Q-T interval on the ECG. Other testing may include:

Your doctor will also ask you if you have a:

  • Family history of LQTS
  • Family history of unexplained fainting, seizures, or cardiac arrest
  • History of fainting, seizures or cardiac arrest, especially with exercise

Last reviewed by a Cleveland Clinic medical professional on 05/01/2019.

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