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