What Causes Long QT Syndrome?

Inherited Long QT Syndrome

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

If you have inherited LQTS, you received the faulty gene(s) from one or both of your parents. Inherited LQTS is a lifelong condition.

There are seven known types of inherited LQTS (types 1 though 7). The most common types of inherited LQTS are types 1, 2, and 3. Some types of LQTS stem from either 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're surprised or experience emotional stress.

During these situations, you may develop a rapid and uncontrollable heart rhythm that prevents your heart from pumping blood. This will result in death 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 and 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

Certain medicines or other medical conditions can cause acquired, or noninherited, LQTS.

Medication-Induced Long QT Syndrome

Presently, more than 50 medicines have been recognized to cause 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

Some people who have medication-induced LQTS also may have an inherited form of the syndrome that doesn't cause symptoms unless they take certain 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

Excessive diarrhea or vomiting that causes a major loss of potassium or sodium ions from the bloodstream may cause LQTS. The syndrome lasts until the levels of these ions in the blood return to normal.

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