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. |