Long Q-T Syndrome

Long Q-T syndrome (LQTS) is an infrequent, hereditary disorder of the heart's electrical rhythm that can occur in otherwise healthy people. It usually affects children or young adults.

When the heart contracts, it emits an electrical signal. This signal can be recorded on an electrocardiogram (ECG) and produces a characteristic waveform. The different parts of this waveform are designated by letters — P, Q, R, S and T. The Q-T interval represents the time for electrical activation and inactivation of the ventricles, the lower chambers of the heart. A doctor can measure the time it takes for the Q-T interval to occur (in fractions of a second), and can tell if it occurs in a normal amount of time. If it takes longer than normal, it's called a prolonged Q-T interval.

What are the symptoms of LQTS?
People with LQTS may not have any symptoms. People who do have symptoms often exhibit fainting (syncope) and abnormal rate and/or rhythm of the heartbeat (arrhythmia). People with this syndrome may show prolongation of the Q-T interval during physical exercise, intense emotion (such as fright, anger or pain) or when startled by a noise. Some arrhythmias are potentially fatal, causing sudden death. In one type of inherited LQTS, the person may also become deaf.

Studies of otherwise healthy people with LQTS indicate that they had at least one episode of fainting by the age of 10. The majority also had a family member with a long Q-T interval. People with LQTS don't necessarily have a prolonged Q-T interval all the time. At the time that they have an electrocardiogram (such as during a routine physical examination), the Q-T interval may actually be normal.

Alternatively, some healthy young people may not have a routine ECG, and LQTS may be suspected because of their family history or because of unexplained fainting episodes. In any family where repeated episodes of fainting or a history of sudden death exists, an investigation of the cause, including LQTS, should be undertaken.

How is LQTS treated?
There are treatments for LQTS, including medications such as beta blockers. Sometimes a surgical procedure is performed, and some people may benefit from an implantable defibrillator.

This content is reviewed regularly. Last updated 09/21/07.