Long QT syndrome (LQTS) is a disorder of the heart's electrical activity. It can cause sudden, uncontrollable, dangerous arrhythmias (ah-RITH-me-ahs) in response to exercise or stress. Arrhythmias are problems with the rate or rhythm of the heartbeat.
People who have LQTS also can have arrhythmias for no known reason. However, not everyone who has LQTS has dangerous heart rhythms. When they do occur, though, they can be fatal.
The term "long QT" refers to an abnormal pattern seen on an EKG (electrocardiogram). An EKG is a test that detects and records the heart's electrical activity.
With each heartbeat, an electrical signal spreads from the top of your heart to the bottom. As it travels, the signal causes the heart to contract and pump blood. An EKG records electrical signals as they move through your heart.
Data from the EKG are mapped on a graph so your doctor can study your heart's electrical activity. Each heartbeat is mapped as five distinct electrical waves: P, Q, R, S, and T.
The electrical activity that occurs between the Q and T waves is called the QT interval. This interval shows electrical activity in the heart's lower chambers, the ventricles (VEN-trih-kuls).
The timing of the heart's electrical activity is complex, and the body carefully controls it. Normally the QT interval is about a third of each heartbeat cycle. However, in people who have LQTS, the QT interval lasts longer than normal.
A long QT interval can upset the careful timing of the heartbeat and trigger dangerous heart rhythms.
For more information about the heart's electrical system, go to the Health Topics How the Heart Works article.
On the surface of each heart muscle cell 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 each cell. This generates the heart's electrical activity.
In people who have LQTS, the ion channels may not work well, or there may be too few of them. This may disrupt electrical activity in the heart's ventricles and cause dangerous arrhythmias.
LQTS often is inherited, which means you're born with the condition and have it your whole life. There are seven known types of inherited LQTS. The most common ones are LQTS 1, 2, and 3.
In LQTS 1, emotional stress or exercise (especially swimming) can trigger arrhythmias. In LQTS 2, extreme emotions, such as surprise, can trigger arrhythmias. In LQTS 3, a slow heart rate during sleep can trigger arrhythmias.
You also can acquire LQTS. This means you aren't born with the disorder, but you develop it during your lifetime. Some medicines and conditions can cause acquired LQTS. (For more information, go to "What Causes Long QT Syndrome?")
More than half of the people who have untreated, inherited types of LQTS die within 10 years. However, lifestyle changes and medicines can help people who have LQTS prevent complications and live longer.
Some of these lifestyle changes and treatments include:
If you have LQTS, talk with your doctor about which lifestyle changes and treatments are best for you.
Long QT syndrome (LQTS) can be inherited or acquired. "Inherited" means you're born with the condition and have it your whole life. Inherited conditions are passed from parents to children through genes. "Acquired" means you aren't born with the condition, but you develop it during your lifetime.
Faulty genes cause inherited LQTS. These genes control the production of certain types of ion channels in your heart. Faulty genes may cause the body to make too few ion channels, ion channels that don't work well, or both.
There are seven known types of inherited LQTS (types 1 though 7). The most common types are LQTS 1, 2, and 3.
Some types of LQTS involve faulty or lacking potassium ion or sodium ion channels.
If you have LQTS 1 or LQTS 2, the flow of potassium ions through the ion channels in your heart cells isn't normal. This may cause problems when you exercise or when you have strong emotions.
You may develop a rapid, uncontrollable heart rhythm that prevents your heart from pumping blood. This type of heart rhythm can be fatal if it's not quickly brought under control.
If you have LQTS 3, the flow of sodium ions through ion channels in your heart cells isn't normal. This can trigger a rapid, uncontrollable heart rhythm that can be fatal. In LQTS 3, problems usually occur when your heart beats slower than normal, such as during sleep.
Some medicines and conditions can cause acquired LQTS.
More than 50 medicines have been found to cause LQTS. Some common medicines that may cause the disorder include:
Some people who have medication-induced LQTS also may have an inherited form of the disorder. They may not have symptoms unless they take medicines that lengthen the QT interval or lower potassium levels in the blood. When LQTS doesn't cause symptoms, it's called silent LQTS.
Severe diarrhea or vomiting that causes a major loss of potassium or sodium ions from the bloodstream may cause LQTS. The disorder lasts until these ion levels return to normal.
The eating disorders anorexia nervosa and bulimia and some thyroid disorders may cause a drop in potassium ion levels in the blood, causing LQTS.
Long QT syndrome (LQTS) is a rare disorder. Experts think that about 1 in 7,000 people has LQTS. But no one knows for sure, because LQTS often goes undiagnosed.
LQTS causes about 3,000 to 4,000 sudden deaths in children and young adults each year in the United States. Unexplained sudden deaths in children are rare. When they do occur, LQTS often is the cause.
Inherited LQTS usually is first detected during childhood or young adulthood. Half of all people who have LQTS have their first abnormal heart rhythm by the time they're 12 years old, and 90 percent by the time they're 40 years old. The condition rarely is diagnosed after age 40.
In boys who have LQTS, the QT interval (which can be seen on an EKG test) often returns toward normal after puberty. If this happens, the risk of LQTS symptoms and complications goes down.
LQTS is more common in women than men. Women who have LQTS are more likely to faint or die suddenly from the disorder during menstruation and shortly after giving birth.
Children who are born deaf also are at increased risk for LQTS. This is because the same genetic problem that affects hearing also affects the function of ion channels in the heart.
You're at risk of having LQTS if anyone in your family has ever had it. Unexplained fainting or seizures, drowning or near drowning, and unexplained sudden death are all possible signs of LQTS.
You're also at risk for LQTS if you take medicines that make the QT interval longer. Your doctor can tell you whether your prescription or over-the-counter medicines might do this.
You also may develop LQTS if you have excessive vomiting or diarrhea or other conditions that cause low blood levels of potassium or sodium. These conditions include the eating disorders anorexia nervosa and bulimia, as well as some thyroid disorders.
If you have long QT syndrome (LQTS), you can have sudden and dangerous arrhythmias (abnormal heart rhythms). Signs and symptoms of LQTS-related arrhythmias often first occur during childhood and include:
Often, people who have LQTS 3 develop an abnormal heart rhythm during sleep. This may cause noisy gasping while sleeping.
Sometimes long QT syndrome doesn't cause any signs or symptoms. This is called silent LQTS. For this reason, doctors often advise family members of people who have LQTS to be tested for the disorder, even if they have no symptoms.
Medical and genetic tests may reveal whether these family members have LQTS and what type of the condition they have.
Cardiologists diagnose and treat long QT syndrome (LQTS). Cardiologists are doctors who specialize in diagnosing and treating heart diseases and conditions. To diagnose LQTS, your cardiologist will consider your:
An EKG is a simple test that detects and records the heart's electrical activity. This test may show a long QT interval and other signs that suggest LQTS. Often, doctors first discover a long QT interval when an EKG is done for another suspected heart problem.
Not all people who have LQTS will always have a long QT interval on an EKG. The QT interval may change from time to time; it may be long sometimes and normal at other times. Thus, your doctor may want you to have several EKG tests over a period of days or weeks. Or, your doctor may have you wear a device called a Holter monitor.
A Holter monitor records the heart's electrical activity for a full 24- or 48-hour period. It can detect heart problems that occur for only a few minutes out of the day.
You wear small patches called electrodes on your chest. Wires connect the patches to a small, portable recorder. You can clip the recorder to a belt, keep it in a pocket, or hang it around your neck.
While you wear the monitor, you do your usual daily activities. You also keep a notebook, noting any symptoms you have and the time they occur. You then return both the recorder and the notebook to your doctor to read the results. Your doctor can see how your heart was beating at the time you had symptoms.
Some people have a long QT interval only while they exercise. For this reason, your doctor may recommend that you have a stress test.
During a stress test, you exercise to make your heart work hard and beat fast. An EKG is done while you exercise. If you can't exercise, you may be given medicine to increase your heart rate.
Your doctor will ask whether you've had any symptoms of an abnormal heart rhythm. Symptoms may include:
Your doctor may ask what over-the-counter, prescription, or other drugs you take. He or she also may want to know whether anyone in your family has been diagnosed with or has had signs of LQTS. Signs of LQTS include unexplained fainting, drowning, sudden cardiac arrest, or sudden death.
Your doctor will check you for signs of conditions that may lower blood levels of potassium or sodium. These conditions include the eating disorders anorexia nervosa and bulimia, excessive vomiting or diarrhea, and certain thyroid disorders.
Genetic blood tests can detect some forms of inherited LQTS. If your doctor thinks that you have LQTS, he or she may suggest genetic testing. Genetic blood tests usually are suggested for family members of people who have LQTS as well.
However, genetic tests don't always detect LQTS. So, even if you have the disorder, the tests may not show it.
Also, some people who test positive for LQTS don't have any signs or symptoms of the disorder. These people may have silent LQTS. Less than 10 percent of these people will faint or suddenly die from an abnormal heart rhythm.
Even if you have silent LQTS, you may be at increased risk of having an abnormal heart rhythm while taking medicines that affect potassium ion channels or blood levels of potassium.
If you have inherited LQTS, it may be helpful to know which type you have. This will help you and your doctor plan your treatment and decide which lifestyle changes you should make.
To find out what type of LQTS you have, your doctor will consider:
The goal of treating long QT syndrome (LQTS) is to prevent life-threatening, abnormal heart rhythms and fainting spells.
Treatment isn't a cure for the disorder and may not restore a normal QT interval on an EKG (electrocardiogram). However, treatment greatly improves the chances of survival.
Your doctor will recommend the best treatment for you based on:
People who have LQTS without symptoms may be advised to:
The type of medicine you take will depend on the type of LQTS you have. For example, doctors usually will prescribe sodium channel blocker medicines only for people who have LQTS 3.
If your doctor thinks you're at increased risk for LQTS complications, he or she may suggest more aggressive treatments (in addition to medicines and lifestyle changes). These treatments may include:
People at increased risk are those who have fainted or who have had dangerous heart rhythms from their LQTS.
If possible, try to avoid things that can trigger abnormal heart rhythms. For example, people who have LQTS should avoid medicines that lengthen the QT interval or lower potassium blood levels. (For more information, go to "What Causes Long QT Syndrome?")
Many people who have LQTS also benefit from adding more potassium to their diets. Check with your doctor about eating more potassium-rich foods (such as bananas) or taking potassium supplements daily.
Beta blockers are medicines that prevent the heart from beating faster in response to physical or emotional stress. Most people who have LQTS are treated with beta blockers.
Doctors may suggest that people who have LQTS 3 take sodium channel blockers, such as mexiletine. These medicines make sodium ion channels less active.
Pacemakers and ICDs are small devices that help control abnormal heart rhythms. Both devices use electrical currents to prompt the heart to beat normally. Surgeons implant pacemakers and ICDs in the chest or belly with a minor procedure.
The use of these devices is similar in children and adults. However, because children are still growing, other issues may arise. For example, as children grow, they may need to have their devices replaced.
People who are at high risk of death from LQTS sometimes are treated with surgery. During surgery, the nerves that prompt the heart to beat faster in response to physical or emotional stress are cut.
This type of surgery keeps the heart beating at a steady pace and lowers the risk of dangerous heart rhythms in response to stress or exercise.
Long QT syndrome (LQTS) usually is a lifelong condition. The risk of having an abnormal heart rhythm that leads to fainting or sudden cardiac arrest may lessen as you age. However, the risk never completely goes away.
You'll need to take certain steps for the rest of your life to prevent abnormal heart rhythms. You can:
If an abnormal heart rhythm does occur, you'll need to seek treatment right away.
If exercise triggers an abnormal heart rhythm, your doctor may tell you to avoid any strenuous exercise, especially swimming. Ask your doctor what types and amounts of exercise are safe for you.
If you have a pacemaker or implantable cardioverter defibrillator, avoid contact sports that may dislodge these devices. You may want to exercise in public or with a friend who can help you if you faint.
Avoid medicines that can trigger an abnormal heart rhythm. This includes some medicines used to treat allergies, infections, high blood pressure, high blood cholesterol, depression, and arrhythmias. Talk with your doctor before taking any prescription, over-the-counter, or other medicines or drugs.
Seek medical care right away for conditions that lower the sodium or potassium level in your blood. These conditions include the eating disorders anorexia nervosa and bulimia, excessive vomiting or diarrhea, and certain thyroid disorders.
If you have LQTS 2, try to avoid unexpected noises, such as loud or jarring alarm clock buzzers and telephone ringers.
You may want to wear a medical ID necklace or bracelet that states that you have LQTS. This will help alert medical personnel and others about your condition if you have an emergency.
Let your roommates, coworkers, or other people with whom you have regular contact know that you have a condition that might cause you to faint or go into cardiac arrest. Tell them to call 9–1–1 right away if you faint.
Consider asking a family member and/or coworker to learn cardiopulmonary resuscitation (CPR) in case your heart stops beating.
You also may want to keep an automated external defibrillator (AED) with you at home or at work. This device uses electric shocks to restore a normal heart rhythm.
Someone at your home and/or workplace should be trained on how to use the AED, just in case your heart stops beating. If a trained person isn't available, an untrained person also can use the AED to help save your life.
If you have LQTS 3 and you sleep alone, you may want to have an intercom in your bedroom that's connected to someone else's bedroom. This will let others detect the noisy gasping that often occurs if you have an abnormal heart rhythm while lying down.
You should see your cardiologist (heart specialist) regularly. He or she will adjust your treatment as needed. For example, if you still faint often while using less aggressive treatments, your doctor may suggest other treatment options.
Living with LQTS may cause fear, anxiety, depression, and stress. Talk about how you feel with your health care team. Talking to a professional counselor also can help. If you're very depressed, your doctor may recommend medicines or other treatments that can improve your quality of life.
Joining a patient support group may help you adjust to living with LQTS. You can see how other people have coped with the condition. Talk with your doctor about local support groups or check with an area medical center.
Support from family and friends also can help relieve stress and anxiety. Let your loved ones know how you feel and what they can do to help you.
Some people learn they have LQTS because they're tested after a family member dies suddenly from LQTS. Grief counseling may help you cope if this has happened to you. Talk with your doctor about finding a grief counselor.
The National Heart, Lung, and Blood Institute (NHLBI) is strongly committed to supporting research aimed at preventing and treating heart, lung, and blood diseases and conditions and sleep disorders.
NHLBI-supported research has led to many advances in medical knowledge and care. Often, these advances depend on the willingness of volunteers to take part in clinical trials.
Clinical trials test new ways to prevent, diagnose, or treat various diseases and conditions. For example, new treatments for a disease or condition (such as medicines, medical devices, surgeries, or procedures) are tested in volunteers who have the illness. Testing shows whether a treatment is safe and effective in humans before it is made available for widespread use.
By taking part in a clinical trial, you can gain access to new treatments before they're widely available. You also will have the support of a team of health care providers, who will likely monitor your health closely. Even if you don't directly benefit from the results of a clinical trial, the information gathered can help others and add to scientific knowledge.
If you volunteer for a clinical trial, the research will be explained to you in detail. You'll learn about treatments and tests you may receive, and the benefits and risks they may pose. You'll also be given a chance to ask questions about the research. This process is called informed consent.
If you agree to take part in the trial, you'll be asked to sign an informed consent form. This form is not a contract. You have the right to withdraw from a study at any time, for any reason. Also, you have the right to learn about new risks or findings that emerge during the trial.
For more information about clinical trials related to long QT syndrome, talk with your doctor. You also can visit the following Web sites to learn more about clinical research and to search for clinical trials:
For more information about clinical trials for children, visit the NHLBI's Children and Clinical Studies Web page.
The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.