Long QT Syndrome
Long QT syndrome is an abnormality of the heart's electrical system, (see Section 3, Chapter 27) which may cause loss of consciousness or sudden death.
Long QT syndrome may affect as many as 1 of 7,000 people. In the United States, it may cause sudden death in 3,000 to 4,000 children and young adults each year. In children, this disorder is usually due to a genetic abnormality. A person with the disorder may have family members who died suddenly and inexplicably. In most adults, long QT syndrome is caused by use of a drug or a disorder.
People who have long QT syndrome are predisposed to developing an unusually fast heart rate, which often occurs during physical activity or emotional excitement. When the heart rate is too fast, the brain may not receive enough blood. The result is loss of consciousness. Some people with long QT syndrome are also born deaf. But about one third of people have no symptoms. Long QT syndrome can cause sudden death at a young age.
Doctors may recommend electrocardiography (ECG (see Section 3, Chapter 21)) for children or young adults who have suddenly and inexplicably lost consciousness. The procedure may be performed with the person at rest or after receiving intravenous drugs or the person may be asked to walk on a treadmill or pedal an exercise bicycle in a procedure called exercise stress testing.
Beta-blockers are effective for most children and adults. Some adults may benefit from mexiletine, an antiarrhythmic drug. For children and adults who do not respond to drugs, a pacemaker or a combination pacemaker-internal defibrillator may be tried. An internal defibrillator can shock the heart, reviving the person, whenever the heart develops a lethal rhythm abnormality. Occasionally, as an alternative, a nerve in the neck is cut in a procedure called cervicothoracic sympathectomy. Cutting this nerve can help prevent the fast heart rate that causes sudden death.
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