Long QT syndrome is a heart rhythm disorder caused by changes in the heart's electrical recharging system. It doesn't affect the heart's structure.
In a typical heart, the heart sends blood out to the body during each heartbeat. The heart's chambers squeeze (contract) and relax to pump the blood. This coordinated action is controlled by the heart's electrical system. Electrical signals (impulses) travel from the top to the bottom of the heart. The tell the heart to contract and beat. After each heartbeat, the system recharges to prepare for the next heartbeat.
In long QT syndrome, the heart's electrical system takes longer than usual to recharge between beats. This delay is called a prolonged QT interval. It may be seen on an electrocardiogram (ECG).
Long QT syndrome is often grouped into two main categories, depending on the cause.
- If you are born with the condition, it's called congenital long QT syndrome. Some forms of long QT syndrome result from altered DNA that is passed down through families (inherited).
- If an underlying medical condition or medication causes it, it's called acquired long QT syndrome. This type of long QT syndrome is usually reversible when the underlying cause is identified and treated.
Causes of congenital long QT syndrome
More than a dozen genes have been linked to long QT syndrome so far. Researchers have identified hundreds of alterations within these genes.
There are two forms of congenital long QT syndrome:
- Romano-Ward syndrome (autosomal dominant form). This more common form occurs in people who inherit only a single gene variant from one parent.
- Jervell and Lange-Nielsen syndrome (autosomal recessive form). Episodes of this rare form of LQTS usually occur very early in life and are more severe. In this syndrome, children receive the altered gene variants from both parents. The children are born with long QT syndrome and deafness.
Causes of acquired long QT syndrome
More than 100 medications — many of them common — can cause prolonged QT intervals in otherwise healthy people.
If a medication causes acquired long QT syndrome (LQTS), the condition may be called drug-induced long QT syndrome. Medications that can cause LQTS include:
- Certain antibiotics, such as erythromycin (Eryc, Erythrocin, others), azithromycin (Zithromax) and others
- Certain antifungal pills used to treat yeast infections
- Diuretics that cause an electrolyte imbalance (low potassium, most commonly)
- Heart rhythm drugs (anti-arrhythmics) that lengthen the QT interval
- Some antidepressant and antipsychotic medications
- Some anti-nausea medications
Always tell your health care provider about all the medications you take, including those you buy without a prescription.
Health conditions that can lead to acquired long QT syndrome include:
- Body temperature below 95 degrees Fahrenheit (37 degrees Celsius), a condition called hypothermia
- Low calcium (hypocalcemia)
- Low magnesium (hypomagnesemia)
- Low potassium (hypokalemia)
- Noncancerous tumor of the adrenal gland (pheochromocytoma)
- Stroke or brain (intracranial) bleed
- Underactive thyroid (hypothyroidism)