Long QT syndrome

Overview

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 to 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 a fifty-fifty chance of inheriting the gene. Once a family member is identified with LQTS, it is very important to test all other family members.

Signs & symptoms

The most common symptom of Long QT Syndrome (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.

Diagnosis

Long QT syndrome (LQTS) may occur spontaneously with unpredictable timing. Therefore, in many cases, specialized tests are needed to make an accurate diagnosis. If your doctor suspects that your child has an arrhythmia caused by LQTS, he or she will order one or more of the following diagnostic tests to determine the source of your child's symptoms.

• Electrocardiogram (ECG or EKG) — An ECG records the heart's electrical activity. Small patches called electrodes are placed on your child's chest, arms and legs, and are connected by wires to the ECG machine. The electrical impulses of your child's heart are translated into a graph or chart, enabling doctors to determine the pattern of electrical current flow in the heart and to diagnose arrhythmias.
• Exercise Stress Test — An exercise stress or treadmill test records the electrical activity of your child's heart during exercise, which differs from the heart's electrical activity at rest.
• Event Monitor — This is a small monitor about the size of a pager that your child can have for up to a month. Since the arrhythmia may occur at unpredictable times, this will help to record the abnormal rhythm when your child is experiencing symptoms. He or she can just push a button on the pager and record the heartbeat. The recording can then be transmitted by phone to the doctor.
• Genetic Blood Testing — A genetic blood test called FAMILION is now available to diagnose LQTS. During the test, genetic material (DNA) is removed from the blood sample of a patient who has been diagnosed with or may have LQTS. The patient's DNA is examined to identify any alterations, also known as mutations, in the five cardiac ion channel genes that may cause LQTS.
• Holter Monitor — A Holter monitor is a small, portable machine that your child wears for 24 hours. It is about the size of a portable tape player and provides a continuous 24-hour recording of your child's heartbeat onto a tape. You will be asked to keep a diary of your child's activities and symptoms. This monitor may detect arrhythmias that might not show up on a resting electrocardiogram, which only records a heartbeat for a few seconds at rest.

Treatment

Treatment is required for all patients with LQTS. The usual treatment is beta-blocker medications, the dose varying for each patient. Your child's doctor will monitor and adjust the dosage based on your child's heart rate, relief of symptoms and the results of their diagnostic tests.

It is extremely important that medications for LQTS are taken every day and not missed. Medications are not a cure, but protect against episodes of fast heart rhythms if taken as prescribed.

Another common form of treatment for children with LQTS is an implantable cardioverter-defibrillator (ICD). The ICD is a small electronic device that is inserted into the body and monitors the heart rhythm at all times. If it senses a dangerously fast heart rhythm, the ICD delivers electrical impulses or shocks to restore a normal rhythm.