Abnormal Heart Rhythm

Long QT Syndrome

Signs and Symptoms
Diagnosis
Treatment

Signs and Symptoms

Long QT syndrome (LQTS) is an abnormality in the heart's electrical system that may cause very fast and potentially dangerous heart rhythms -- arrhythmias called torsade de pointes. These arrhythmias may cause sudden loss of consciousness and in some cases, sudden cardiac death. QT refers to a time interval measured on the electrocardiogram (ECG), which is a picture of the electrical activity of heartbeats.

Although the exact frequency of LQTS is unknown, it may be as prevalent as 1 in 5,000 people and may cause 2,000 - 3,000 sudden deaths in children and young adults each year in the United States. However, it is important to note that with the correct diagnosis and therapy, LQTS is a treatable disorder and most deaths are preventable.

LQTS may either be inherited as a genetic heart abnormality or acquired, most often through the administration of drugs. However, in most instances, the condition is inherited, which means it may affect multiple family members. Each child has an independent 50/50 chance of inheriting the gene. Once a family member is identified with LQTS, it is very important to test all other family members.

The most common symptom of LQTS is a sudden loss of consciousness, also known as syncope. The condition may also cause seizures and in some instances, cardiac arrest and sudden death.

Some children with LQTS never experience syncope and others may have frequent episodes that could possibly lead to cardiac arrest and sudden death. It is important to note that symptoms usually occur without warning and are caused by a very fast heart rhythm called torsade de pointes. Syncope may occur during or just after physical exertion, emotional excitement or sudden auditory arousal, such as from an alarm clock.

In children who experience syncope only, the torsade de pointes rhythm returns to a normal rhythm, usually within a minute, and the child regains consciousness. In a minority of patients, the torsade rhythm may persist and deteriorate into ventricular fibrillation, a condition in which the heart's electrical activity becomes disordered. When this happens, the heart's ventricles, the lower chambers that pump blood, contract in a rapid, unsynchronized way, which may cause sudden death.

Reviewed by health care specialists at UCSF Children's Hospital.
Last updated May 8, 2007