What Is Long QT Syndrome?

Long QT syndrome (LQTS) is a disorder of the heart's electrical activity that may cause you to develop a sudden, uncontrollable, and dangerous heart rhythm (called an arrhythmia) in response to exercise or stress. Such abnormal heart rhythms also can develop for no known reason in people who have LQTS. Not everyone who has LQTS develops a dangerous heart rhythm, but if one does occur, it may be fatal.

The term "long QT" refers to an abnormality seen on an EKG (electrocardiogram). An EKG is a test that detects and records the electrical activity of the heart. The QT interval, recorded on the EKG, corresponds to the time during which the lower chambers of your heart (the ventricles) are triggered to contract and then build the potential to contract again.

The timing of the electrical activity of the heartbeat is complex and carefully controlled by the body. Normally the QT interval of the heartbeat lasts about a third of each heartbeat cycle on the EKG. But in people with LQTS, the QT interval usually lasts longer than normal, which can upset the careful timing of the heartbeat and trigger a dangerous, irregular rhythm.

Overview

On the surface of each muscle cell in the heart are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium, and potassium atoms (ions) flow into and out of the cell. This generates the electrical activity of the heart.

This activity causes each heart cell to contract. Normally, the electrical activity spreads from one heart cell to the next in an orderly and coordinated way to allow the heart to pump blood. During each normal heartbeat, the muscle cells in the upper chambers of the heart, the atria (AY-tree-uh), contract. The contraction pumps blood from the atria to the ventricles. Then the muscle cells in the ventricles contract, pumping blood from the ventricles to the lungs and the rest of the body. This coordinated contraction of the atria and ventricles represents one normal heartbeat. (See the Diseases and Conditions Index article on How the Heart Works for more information on the heart's electrical system.)

In people who have LQTS, problems with the ion channels in the heart cells may disrupt the timing of the electrical activity in the ventricles. The ion channels may not work properly, or there may be too few of them. In this situation, the heart may suddenly develop a fast and abnormal heart rhythm that can be life threatening.

Many cases of LQTS are inherited, which means you are born with the condition and have it your whole life. There are seven known types of inherited LQTS. The most common ones are called LQTS 1, LQTS 2, and LQTS 3.

Emotional stress or physical exercise (especially swimming) that makes the heart beat faster tends to trigger irregular heart rhythms if you have LQTS 1. In LQTS 2, irregular rhythms may be triggered by surprise or other extreme emotions. In LQTS 3, a low heart rate during sleep may be the trigger for an irregular heart rhythm.

Acquired, or noninherited, LQTS may be brought on by certain medicines and other medical conditions.

Outlook

More than half the people who have an untreated, inherited form of LQTS die within 10 years. But for many people with LQTS, lifestyle changes and medical treatments can help prevent dangerous complications and lengthen life expectancy. Some of these changes include:

• Avoiding strenuous physical activity or startling noises
• Adding more potassium to your diet
• Taking heart medicines called beta blockers, which are very effective at preventing sudden cardiac arrest
• Having an implantable device, such as a pacemaker or implantable cardioverter defibrillator, that helps control abnormal heart rhythms

Discuss with your doctor the lifestyle changes and treatments that are appropriate for you and the type of LQTS you have.

July 2007