What Causes Long QT Syndrome?

Inherited Long QT Syndrome

Faulty genes that control the production of certain types of ion channels in your heart cells cause inherited long QT syndrome (LQTS). These LQTS genes may cause the body to produce too few ion channels or ion channels that don't work as they should, 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 LQTS types stem from faulty or lacking potassium ion channels, while others are due to faulty or lacking sodium channels.

If you have LQTS 1 and LQTS 2, the flow of potassium ions through the ion channels in your heart cells isn't normal, which 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 may prevent 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, which also may trigger a rapid and uncontrollable heart rhythm that can result in death. In LQTS 3, problems usually develop when your heart beats slower than normal, such as during sleep.

Noninherited Long QT Syndrome

Acquired, or noninherited, LQTS may be brought on by certain medicines and other medical conditions. Side effects from certain medicines are the most common cause of 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 with medication-induced LQTS may also 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. This is sometimes 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.