Long QT syndrome – symptoms, causes, diagnosis, treatment

Long QT syndrome (LQTS) is a heart rhythm disorder that can potentially cause fast, chaotic heartbeats. The rapid heartbeats, caused by changes in the part of your heart that causes it to beat, may lead to fainting. In some cases, your heart’s rhythm may beat so erratically that it can cause sudden death.

You can be born with a genetic mutation that puts you at risk of long QT syndrome. In addition, more than 50 medications, many of them common, may cause long QT syndrome. Medical conditions, such as congenital heart defects, also may cause long QT syndrome.

Long QT syndrome is treatable. You may need to limit your physical activity, avoid certain medications that can cause the condition or take medications to prevent a chaotic heart rhythm (arrhythmia). Some people with long QT syndrome also need an implantable device to control the heart’s rhythm and to prevent against sudden death.


About half those with long QT syndrome don’t have any signs or symptoms. They may be aware of their condition only from results of an electrocardiogram (ECG) performed for an unrelated reason, because they have a family history of long QT syndrome or because of genetic testing results.

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

  • Fainting. This is the most common sign of long QT syndrome. In people with long QT syndrome, fainting spells (syncope) are caused by the heart temporarily beating in an erratic way. These fainting spells may happen when you’re excited, angry, scared, or during exercise. Fainting in people with long QT syndrome can occur without warning, such as losing consciousness after being startled by a ringing telephone.

    Signs and symptoms that you’re about to faint include lightheadedness, heart palpitations or irregular heartbeat, weakness and blurred vision. If you think you’re about to faint, sit or lie down and tell someone near you about your symptoms. However, in long QT syndrome, such warning signs before fainting are unusual.

  • Seizures. If the heart continues to beat erratically, the brain becomes increasingly deprived of oxygen. This can then cause generalized seizures. In fact, some people with long QT syndrome have been misdiagnosed as having a seizure disorder and have even been treated with anti-epileptic medications.
  • 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 will occur.

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. Most LQTS-related deaths occur in people ages 11 to 30.

Rarely, signs and symptoms of long QT syndrome may occur during sleep or arousal from sleep. Some doctors believe that inherited LQTS-causing mutations likely explain about 10 percent to 15 percent of sudden infant death syndrome (SIDS).


Your heart beats about 100,000 times a day to circulate blood throughout your body. To pump blood, your heart’s chambers contract and relax. These actions are controlled by electrical impulses created in the sinus node, a group of cells in the upper right chamber of your heart. These impulses travel through your heart and cause it to beat.

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 (a process known as repolarization). This electrical disturbance can be seen on an electrocardiogram (ECG).

Prolonged QT interval
An electrocardiogram (ECG) 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 as waves of electrical activity.

An ECG measures electrical impulses as five distinct waves. Doctors label these five waves using the letters P, Q, R, S and T. The waves labeled Q through T show electrical activity in your heart’s lower chambers.

The space 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 to contract and then refill with blood 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 due to an underlying medical condition or a medication.

Inherited long QT syndrome
At least 12 genes associated with long QT syndrome have been discovered so far, and hundreds of mutations within these genes have been identified. Mutations in three of these genes account for about 75 percent of long QT syndrome.

Doctors have described two forms of inherited long QT syndrome:

  • Romano-Ward syndrome. This more common form occurs in people who inherit only a single genetic variant from one of their parents. This type of long QT syndrome affects about one in 2,500 people.
  • Jervell and Lange-Nielsen syndrome. Signs and symptoms of this rare form 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 and have discovered that about 10 percent to 15 percent of 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 lengthen the QT interval in otherwise healthy people and cause a form of acquired long QT syndrome known as drug-induced long QT syndrome.

Medications that can lengthen the QT interval and upset 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 may also have some subtle genetic defects in their hearts, making them more susceptible to disruptions in heart rhythm 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 is 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.

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 — “twists of the points” — in which your heart’s ventricles beat fast, making the waves on an ECG monitor look twisted. When this arrhythmia occurs, less blood is pumped out from your heart. Less blood then reaches your brain, causing you to faint.

If a torsades de pointes episode is short — lasting less than one minute — your heart can correct itself seconds later, and you regain consciousness on your own. However, if a torsades de pointes episode 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. It’s thought that long QT syndrome may explain some cases of sudden death in young people who otherwise appear healthy.


If your doctor suspects that you have long QT syndrome, you may need to have several tests to confirm the diagnosis. These include:

  • An electrocardiogram (ECG). In this noninvasive test, small probes are taped to your chest to monitor the waves of electrical impulses in your heart. The probes transmit the waves to a computer screen or printout for your doctor to see. You may have this test while at rest or while exercising by running on a treadmill or pedaling a stationary bike.
  • 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.

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

  • 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 this stress test, doctors monitor the effects of the adrenaline on the way your heart recharges. This test can unmask in some patients what’s known as concealed long QT syndrome, which is a normal QT interval (recharging time) at rest, although they still have the syndrome. 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.
  • 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 is available. 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 still have long QT syndrome. If your genetic cause of long QT syndrome is discovered through a positive genetic test, then family members can be tested to prove definitively whether they inherited the same genetic mutation.

In addition to these tests, your doctor will need to know your medical history and what medications you take.

There’s some speculation that long QT syndrome may be over-diagnosed, especially in children, adolescents and young adults. Because treatments for long QT syndrome can be life altering, such as avoiding strenuous exercise or taking powerful medications, you may want to seek a second opinion if your doctor diagnoses you with long QT syndrome.


Treatment for inherited long QT syndrome can involve medications, medical devices, surgery or lifestyle changes. The goal of treatment is either to prevent the long QT heart from ever beating out of control or to prevent sudden death.

It’s often 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 used to treat long QT syndrome include:

  • Beta blockers. Examples of this heart drug include nadolol (Corgard) and propranolol (Inderal). These drugs slow the heart rate and prevent the dangerously fast heartbeats that can come about in times of stress, fear or exertion for 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 supplements may improve the heart’s recharging system 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 won’t cure the condition, they provide some protection against potentially fatal disruptions of your heart rhythm. You may need to take a medication such as a beta blocker indefinitely.

Medical devices and surgical procedures
Your doctor may consider two other treatments for you:

  • A pacemaker or implantable cardioverter-defibrillator (ICD). These devices can monitor for and, if necessary, stop a potentially fatal arrhythmia. Each device is implanted under the skin of your chest and will correct your heart’s rhythm if it detects a disrupted heart rhythm.
  • Left-sided sympathetic denervation surgery. In this procedure, specific nerves in your 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 sudden death.

Lifestyle changes
In addition to medications or surgery, your doctor will likely recommend lifestyle changes to reduce your symptoms. These could include avoiding strenuous exercise or contact sports, reducing loud, startling noises, and staying away from situations that could make you excited or angry.

If your symptoms are mild or don’t occur very often, your doctor may recommend only lifestyle changes as treatment for your condition.


Once you’ve been diagnosed with 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.

    Strenuous exercise may be dangerous and is not recommended for some people with long QT syndrome. However, other people may be at such low risk of complications that they may be able to continue strenuous exercise and competitive sports. Discuss this issue with your doctor carefully.

  • Know your symptoms. Be fully aware of symptoms that can warn you of irregular heart rhythms and decreased blood flow to your brain. Remember, a fainting episode from long QT syndrome is the most important warning sign for future, more-dangerous long QT events.
  • 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 (AED) may be appropriate.

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

Sexual intercourse doesn’t appear to increase the risk of 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.


If you have inherited long QT syndrome, be careful about which medications you take. Some medications — including certain appetite suppressants, decongestants and common antibiotics, such as erythromycin — 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.

Long QT syndrome can be a worrisome condition because of its serious potential outcomes. Worrying about possible fatal heart rhythms can obviously cause you and your family a lot of stress.

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.