Causes and Risk Factors

What are the causes of Long QT Syndrome?

LQTS is a rare condition that is usually inherited. It is often first detected in children and young adults. LQTS also may be acquired, rather than inherited, and caused by certain medicines and conditions.

  • About 1 in 5000-7,000 people has LQTS. But no one knows for sure because LQTS often goes undiagnosed.2
  • LQTS causes about 3,000 to 4,000 sudden deaths in children and young adults each year in the United States. Unexplained sudden death in children is rare. But when it does occur, LQTS often is the cause.2

Inherited LQTS and the Ion Channel
Inherited LQTS usually is first detected during childhood or young adulthood. Half of all people who have LQTS have their first abnormal heartbeat by the time they are 12 years old, and 90 percent by the time they are 40 years old. The condition rarely is diagnosed in someone after age 40.2

The heart relies on the ion channels to create the electrical activity in the heart muscle that makes the heart beat.

  • On the surface of each muscle cell in the heart 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 the cell.
  • The action of the ion channels generates the electrical activity used to make the heart beat.

Normally, the electrical activity of the heart spreads from one heart cell to the next in an orderly and coordinated way, like dominoes. In people who have LQTS, the ion channels may not work properly, or there may be too few of them. In this situation, the heart may suddenly develop a fast and abnormal heart rhythm that can be life threatening.

Many cases of LQTS are inherited, which means you're born with the condition and have it your whole life. There are seven known types of inherited LQTS. The most common ones are called LQTS 1, LQTS 2, and LQTS 3. Women who have LQTS are more likely to faint or die suddenly from the condition during menstruation and shortly after giving birth.2 In boys who have LQTS, the QT interval (on the ECG) often returns toward normal after puberty.2

Risk Factors

Emotional stress or exercise (especially swimming) that makes the heart beat fast tends to trigger abnormal heart rhythms if you have LQTS 1. In LQTS 2, abnormal rhythms may be triggered by surprise or other extreme emotions. In LQTS 3, a slow heart rate during sleep may trigger an abnormal heart rhythm.

Major Risk Factors
You are at risk for having LQTS if:

  • Anyone in your family has ever had it. Unexplained fainting or seizures, drowning or near drowning, or unexplained sudden death are all possible signs of LQTS.
  • If you take medicines that make the QT interval longer. Your doctor can tell you whether prescription or over-the-counter medicines you take might do this.
  • if you have excessive vomiting or diarrhea or other conditions that cause low blood levels of potassium or sodium. These conditions include the eating disorders anorexia nervosa and bulimia and certain thyroid disorders.

Certain medicines or other medical conditions can cause acquired, or non-inherited, LQTS. Some of the commonly used medicines that may cause LQTS include:

  • Antihistamines and decongestants
  • Diuretics (pills that remove excess water from your body)
  • Antibiotics
  • Antidepressants
  • Cholesterol-lowering medicines and some diabetes medicines

The risk of developing an abnormal heartbeat that leads to fainting or sudden cardiac arrest may lessen with age, but the risk never disappears.