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
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