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Long QT syndrome (LQTS) is a disorder of the heart's electrical system. The condition leaves you vulnerable to fast, chaotic heartbeats that may lead to fainting — and in some cases, cardiac arrest and possibly sudden death.

You can be born with a genetic predisposition for long QT syndrome. In addition, more than 50 medications, many of them common, as well as other medical conditions, may cause long QT syndrome.

Treatment for long QT syndrome may involve limiting your physical activity, avoiding certain medications or taking medications to prevent the development of a chaotic heart rhythm. Some people with long QT syndrome also need an implantable device to control the heart's rhythm and prevent against sudden death.

Not all people with long QT syndrome experience signs or symptoms. In fact, approximately half will never develop signs and symptoms and may be aware of their condition only from results of an electrocardiogram (ECG) performed because they have a family history of long QT syndrome or for an unrelated reason.

For people who do experience signs and symptoms of long QT syndrome, the most common signs include:

• Fainting. In people with long QT syndrome, fainting spells (syncope) are caused by the heart temporarily beating in an erratic way.
• Seizures. If the heart remains in electrical chaos, the brain becomes increasingly deprived of oxygen. This can cause seizures. In fact, some people with long QT syndrome have been misdiagnosed as having a seizure disorder.
• Sudden death. Normally, the heart returns to its normal rhythm. If this doesn't happen spontaneously and paramedics don't arrive in time to convert the rhythm back to normal with an external defibrillator, sudden death can occur.

The main sign — fainting spells — often occurs during exercise or emotional excitement, such as when you're startled, angry or scared. A person with long QT syndrome may lose consciousness, for example, while playing basketball or after hearing a startling noise, such as an alarm clock going off or a phone ringing.

Signs and symptoms of inherited long QT syndrome may start during the first months of life, or as late as middle age. Most people who experience signs or symptoms from long QT syndrome have their first episode by the time they're age 40. About half have their first cardiac signs or symptoms by age 12.

Rarely, signs and symptoms of long QT syndrome may occur during sleep or arousal from sleep. Some doctors believe that inherited long QT syndrome may explain some cases of sudden infant death syndrome (SIDS).

Your heart beats 100,000 times a day to circulate blood throughout your body. To pump blood, your heart's chambers must contract and relax in a coordinated manner. Contraction and relaxation are controlled by electrical impulses that travel through your heart muscle — like electricity through wires.

Your heart consists of four chambers — two upper chambers (atria) that receive blood and two lower chambers (ventricles) that pump blood. Within the upper-right chamber of your heart is a group of cells called the sinus node. The sinus node produces the electrical impulse that starts each heartbeat.

Each impulse first travels through your heart's atria. The atria contract, squeezing blood into the two ventricles below. The atria relax. The impulse then travels through your ventricles, and the ventricles contract, pumping blood out to your lungs and the rest of your body. The ventricles then relax. This pattern of alternating contraction and relaxation of your heart's upper and lower chambers makes up your heartbeat.

After each heartbeat, your heart's electrical system recharges itself in preparation for the next heartbeat. In long QT syndrome, however, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance can be seen on an electrocardiogram (ECG or EKG).

Prolonged QT interval
An ECG test measures electrical impulses as they travel through your heart. Patches with wires attached to your skin measure these impulses, which are displayed on a monitor or printed on paper.

An ECG measures electrical impulses as five distinct waves. Doctors label these five waves using the letters P, Q, R, S and T. The P wave shows electrical activity in your heart's upper chambers. The other waves, Q through T, reflect electrical activity in your heart's lower chambers.

The interval between the start of the Q wave and the end of the T wave (QT interval) corresponds to the time it takes for your heart's ventricles to contract and then refill before beginning the next contraction. In other words, the QT interval refers to the length of time it takes cells in your heart's lower chambers to electrically discharge and then recharge.

By measuring the QT interval, doctors can tell whether it occurs in a normal amount of time. If it takes longer than normal, it's called a prolonged QT interval.

Long QT syndrome results from abnormalities in the heart's electrical recharging system. However, the heart's structure is normal. Abnormalities in your heart's electrical system may be inherited or acquired.

Inherited long QT syndrome
Genetic variants in at least nine genes are associated with long QT syndrome. Mutations in three key genes account for about 75 percent of long QT syndrome.

Although sporadic or spontaneous mutations can occur, you typically inherit a genetic variant from one of your parents. Rarely, you can receive genetic variants from both parents, which can result in a very severe form of long QT syndrome that's also accompanied by deafness.

Progress has been made in understanding the genetics of inherited long QT syndrome. Before these these newer understandings, doctors initially described two forms of inherited long QT syndrome:

• Romano-Ward syndrome. This more common form occurs in children who inherit only a single genetic variant from one parent.
• Jervell and Lange-Nielsen syndrome. Signs and symptoms of this rare form — named after the researchers who first identified it — usually occur earlier and are more severe than in Romano-Ward syndrome. It's seen in children who are born deaf and have long QT syndrome because they inherited genetic variants from each parent.

Additionally, scientists have been investigating a possible link between SIDS and long QT syndrome. Researchers suspect that some babies with SIDS had a genetic defect or mutation for long QT syndrome.

Acquired long QT syndrome
More than 50 medications, many of them common, can prolong the QT interval in otherwise healthy people and cause a form of acquired long QT syndrome known as drug-induced long QT syndrome.

Medications capable of prolonging the QT interval and upsetting heart rhythm include certain antibiotics, antidepressants, antihistamines, diuretics, heart medications, cholesterol-lowering drugs, diabetes medications, as well as some antifungal and antipsychotic drugs.

People who develop drug-induced long QT syndrome also may have some subtle genetic defects in their hearts, making them more susceptible to arrhythmias from taking drugs that can cause prolonged QT intervals.

People at risk of long QT syndrome include:

• Children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, unexplained seizures or a history of cardiac arrest
• Family members of children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, unexplained seizures or a history of cardiac arrest
• Relatives of persons with known long QT syndrome
• People taking medications known to cause prolonged QT intervals

Long QT syndrome often goes undiagnosed or misdiagnosed as a seizure disorder, such as epilepsy. However, researchers believe that long QT syndrome may be responsible for some otherwise unexplained deaths in children and young adults. For example, an unexplained drowning of a young person may be the first clue to inherited long QT syndrome in a family.

People with low potassium, magnesium or calcium blood levels — such as those with the eating disorder anorexia nervosa — may be susceptible to prolonged QT intervals. Potassium, magnesium and calcium are all important minerals for the health of the heart's electrical system.

Sudden loss of consciousness during physical exertion or emotional excitement or after use of a new medication is a reason to see your doctor.

Because long QT syndrome can occur in families, consider seeing your doctor to be tested for long QT syndrome if a close relative (your parent, sibling or child) has been diagnosed with long QT syndrome.

If your doctor suspects that you have long QT syndrome, you may need to undergo several evaluations using an electrocardiogram to confirm the diagnosis and gauge the severity of the problem. In addition, your medical history and a list of your medications are important in diagnosing long QT syndrome.

While some people with suspected long QT syndrome have a clearly prolonged QT interval on an ECG, others don't, making the condition more difficult to diagnose. Other testing may then be necessary.

You may be referred to a cardiologist — a doctor who specializes in the study of the heart and its function — or a long QT syndrome specialist for additional tests such as:

• An exercise stress test. This ECG test is performed while you're walking on a treadmill or pedaling a stationary bike. By monitoring your heart while it's working harder, your doctor can better assess its function and limits.
• A nonexercise (medication) stress test. This ECG test is performed while you're given a medication that stimulates your heart in a way similar to exercise. The medication is given through a vein in your arm and may include epinephrine (adrenaline). Adrenaline is a substance that your body releases in response to stress. In some people with long QT syndrome, fainting spells are triggered by sudden bursts of adrenaline in the body, such as are experienced during intense exercise or emotional upset.
• Ambulatory ECG monitoring. This test, also called Holter monitoring, is used to monitor your heart for rhythm irregularities during normal activity for an uninterrupted 24-hour period. During the test, electrodes attached to your chest are connected to a portable recorder that attaches to your belt or is carried by a shoulder strap. The recorded information can then be analyzed to check for heart rhythm irregularities, such as prolonged QT intervals.
• Event ECG recording. This is similar to the ambulatory ECG except that you may need to wear a portable ECG recorder for days or weeks as it records your heart rhythms.
• An electroencephalogram (EEG). This test looks for neurological causes of fainting, such as a seizure disorder. The procedure measures the waves of electrical activity the brain produces. Small electrodes attached to your head pick up the electrical impulses from your brain and send them to the EEG machine, which records brain waves.
• Genetic testing. A genetic screening test for five of the most common genes associated with long QT syndrome was introduced in 2004. These five genes explain about three out of every four cases of long QT syndrome. Therefore, it's possible to test negative with the genetic test but yet still have long QT syndrome.

Prolonged QT intervals may never cause any problems. However, physical or emotional stress may "trip up" a heart susceptible to prolonged QT intervals and cause the heart's rhythm to spin out of control.

A prolonged QT interval may trigger a particular irregular heart rhythm (arrhythmia) called torsades de pointes, in which your heart's ventricles beat fast. When this arrhythmia occurs, less blood is pumped out from your heart. Less blood then reaches your brain, causing you to faint.

If torsades de pointes is short lasting — lasting less than one minute — your heart can correct itself and beat normally again seconds later, and you regain consciousness on your own. However, if torsades de pointes persists, it can lead to a life-threatening arrhythmia called ventricular fibrillation.

In ventricular fibrillation, the ventricles beat so fast that your heart quivers and ceases pumping blood. Unless your heart is shocked back into a normal rhythm by a device called a defibrillator, ventricular fibrillation can lead to brain damage and death.

Treatment for inherited long QT syndrome can involve medications, medical devices, surgery or lifestyle changes. The goal of treatment is to control signs and symptoms and to prevent sudden death.

It's possible to eliminate drug-induced long QT syndrome simply by switching medications, with your doctor's direction. Some people, however, may need additional treatment.

Medications
Medications used to treat long QT syndrome include:

• Beta blockers. Examples of this heart drug include nadolol (Corgard) and propranolol (Inderal). This class of drugs slows the heart rate and helps prevent the dangerously fast heartbeats that can come about in times of stress, fear or exertion for people with long QT syndrome. Beta blockers can help prevent symptoms in most people with long QT syndrome.
• Potassium. Potassium is a mineral in your body, derived from your diet, that's important for the health of your heart's electrical system. Potassium supplementation may shorten a prolonged QT interval and may be helpful for people with certain forms of long QT syndrome.

Your doctor may suggest treatment for long QT syndrome even if you don't experience frequent signs or symptoms of the disorder.

If you do need treatment, take the medications your doctor prescribes for long QT syndrome as directed. While medications don't cure the condition, they can provide some protection against potentially fatal arrhythmias. You may need to take a medication such as a beta blocker indefinitely.

Medical devices and surgical procedures
For people with long QT syndrome who haven't been helped by medications or who have experienced cardiac arrest, an artificial pacemaker or implantable cardioverter-defibrillator (ICD) may be implanted under the skin in the chest. These devices can monitor for and, if necessary, stop a potentially fatal arrhythmia.

Another possibility includes a surgical procedure called left-sided sympathetic denervation surgery. In this procedure, specific nerves in the chest are surgically cut. These nerves are part of the body's sympathetic nervous system, which controls automatic functions in the body including regulation of heart rhythm. This surgery is generally reserved for people considered at high-risk of serious complications.

Clinical trials
If you have long QT syndrome, you may be asked to participate in a clinical trial to help doctors learn more about your condition. For example, genetic studies are an important area of research. Scientists are finding that certain treatments work better for certain subtypes of inherited long QT syndrome. In addition, triggers for signs and symptoms may vary depending on what gene is involved.

If you have inherited long QT syndrome, be careful about which medications you take. Some medications — including certain common antibiotics, such as erythromycin, appetite suppressants and decongestants — may trigger dangerous heart rhythms. Ask your doctor what you can and can't take safely. Street drugs such as cocaine and amphetamines pose a serious risk for people with long QT syndrome.

In addition, seek medical treatment right away for illnesses that could result in low blood potassium levels, such as conditions that cause protracted vomiting and diarrhea. Such sicknesses could trigger an episode of long QT syndrome in people at risk. Your doctor may advise you not to take some drugs, such as diuretics, that lower blood potassium levels. Your doctor may also recommend that you avoid products containing caffeine.

For some people — especially older adults with long QT syndrome who haven't had signs or symptoms of the condition in decades — preventive measures may be all the treatment that's required.

Once you've received a diagnosis of long QT syndrome, several steps can help you avoid serious consequences of the illness. These steps include:

• Don't overexert yourself. You don't necessarily have to give up sports if you have long QT syndrome. Your doctor may permit recreational activities as long as you have a buddy along in case you have a fainting episode. In general, people with long QT syndrome should never swim alone.

  Hard and strenuous exercise may be dangerous and is not recommended for some people with long QT syndrome. If you have an implantable cardioverter-defibrillator (ICD), contact sports are definitely out. An impact could harm the device's function. In general, check with your doctor to see what activities are safe for you.

• Know your symptoms. Be fully aware of symptoms that can warn you of irregular heart rhythms and decreased blood flow to your brain — such as heart palpitations, lightheadedness, weakness or blurry vision — so that you can rest or seek help as needed.

• Inform other people. Make family, friends, teachers, neighbors and anyone else who has regular contact with you aware of your heart condition. Wear some sort of medical alert identification to notify health care professionals of your condition.

In addition, have plans in place in the case of an emergency cardiac event. Urge family members to learn cardiopulmonary resuscitation (CPR) so that they can provide immediate resuscitation efforts if it ever becomes necessary. In some situations, possession of or rapid access to an automatic external defibrillator may be appropriate.

• Control startling events as much as possible. Turn down the volume on doorbells and turn off the telephone ringer at night.

Sexual intercourse doesn't appear to pose an increased risk for people with long QT syndrome. Pregnancy and delivery aren't associated with increased risk of symptoms in women with long QT syndrome. Nonetheless, your doctor will want to monitor you closely both during your pregnancy and after if you have inherited long QT syndrome. Women with long QT syndrome are at increased risk during the postpartum period and should be monitored carefully.

Long QT syndrome can be a worrisome condition because of its serious potential outcomes.

In inherited long QT syndrome, the heart may be likened to a "ticking time bomb" and it's largely unknown whether the "bomb" is a dud or about ready to detonate with just the right (or wrong) trigger. This uncertainty can be particularly difficult for you and your family to cope with.

Families with inherited long QT syndrome may find it helpful to talk to a cardiologist with expertise in diagnosing and treating long QT syndrome, a genetics counselor, a psychiatrist or psychologist as well as other families with the condition. Several Web sites provide help for families with the disorder.