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What Causes Long QT Syndrome?

Long QT syndrome (LQTS) can be inherited or acquired. "Inherited" means you're born with the condition and have it your whole life. Inherited conditions are passed from parents to children through genes. "Acquired" means you aren't born with the condition, but you develop it during your lifetime.

Inherited Long QT Syndrome

Faulty genes cause inherited LQTS. These genes control the production of certain types of ion channels in your heart. Faulty genes may cause the body to make too few ion channels, ion channels that don't work well, or both.

There are seven known types of inherited LQTS (types 1 though 7). The most common types are LQTS 1, 2, and 3.

Some types of LQTS involve faulty or lacking potassium ion or sodium ion channels.

If you have LQTS 1 or LQTS 2, the flow of potassium ions through the ion channels in your heart cells isn't normal. This may cause problems when you exercise or when you have strong emotions.

You may develop a rapid, uncontrollable heart rhythm that prevents your heart from pumping blood. This type of heart rhythm can be fatal if it's not quickly brought under control.

If you have LQTS 3, the flow of sodium ions through ion channels in your heart cells isn't normal. This can trigger a rapid, uncontrollable heart rhythm that can be fatal. In LQTS 3, problems usually occur when your heart beats slower than normal, such as during sleep.

Acquired Long QT Syndrome

Some medicines and conditions can cause acquired LQTS.

Medication-Induced Long QT Syndrome

More than 50 medicines have been found to cause LQTS. Some common medicines that may cause the disorder include:

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

Some people who have medication-induced LQTS also may have an inherited form of the disorder. They may not have symptoms unless they take medicines that lengthen the QT interval or lower potassium levels in the blood. When LQTS doesn't cause symptoms, it's called silent LQTS.

Other Causes of Acquired Long QT Syndrome

Severe diarrhea or vomiting that causes a major loss of potassium or sodium ions from the bloodstream may cause LQTS. The disorder lasts until these ion levels return to normal.

The eating disorders anorexia nervosa and bulimia and some thyroid disorders may cause a drop in potassium ion levels in the blood, causing LQTS.

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Long QT Syndrome Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Long QT Syndrome, visit www.clinicaltrials.gov.


 
September 21, 2011 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.