Long QT syndrome (LQTS) is a heart rhythm condition that can potentially cause fast, chaotic heartbeats. These rapid heartbeats might trigger a sudden fainting spell or seizure. In some cases, the heart can beat erratically for so long that it causes sudden death.

You can be born with a genetic mutation that puts you at risk of long QT syndrome. In addition, certain medications and medical conditions might cause long QT syndrome.

Long QT syndrome is treatable. You might need to take medications to prevent a chaotic heart rhythm. In some cases, treatment for long QT syndrome involves surgery or an implantable device. You'll also need to avoid medications known to cause prolonged QT intervals that could trigger your long QT syndrome. Sometimes, certain physical activities or sports may need to be avoided.

Many people who have long QT syndrome don't have any signs or symptoms. You might be aware of your condition only from results of an electrocardiogram (ECG) done for an unrelated reason, because you 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 long QT symptoms include:

  • Fainting. This is the most common sign of long QT syndrome. Long QT syndrome-triggered fainting spells (syncope) are caused by the heart temporarily beating in an erratic way. These fainting spells might happen when you're excited, angry, scared or during exercise.

    Fainting can occur without warning, such as losing consciousness after being startled by a ringing telephone. Unlike normal fainting spells that are preceded by warning signs such as lightheadedness, heart palpitations, irregular heartbeat, weakness and blurred vision, long QT syndrome-triggered fainting spells can occur with little to no warning.

  • Seizures. If the heart continues to beat erratically, the brain becomes increasingly deprived of oxygen, which can cause seizures.
  • Sudden death. Generally, 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 might start during the first weeks to months after birth, or as late as older age, or never at all. Most people who experience signs or symptoms from long QT syndrome have their first episode by age 40.

Signs and symptoms of long QT syndrome might occur during sleep or arousal from sleep.

When to see a doctor

Consult your doctor if you suddenly faint during physical exertion or emotional excitement or after use of a new medication.

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

Long QT syndrome is a heart rhythm disorder that can cause serious irregular heart rhythms (arrhythmias).

In a normal heart, your heart circulates blood throughout your body during each heartbeat. Your heart's chambers contract and relax to pump blood. 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. This process is known as repolarization.

In long QT syndrome, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance, which often can be seen on an electrocardiogram (ECG), is called a prolonged QT interval.

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 (ventricles).

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.

By measuring the QT interval, doctors can measure whether the QT interval occurs in a normal amount of time. If it takes longer than normal to occur, it's called a prolonged QT interval. The upper limit of a normal QT interval takes into account age, sex, and regularity and speed of the heart rate.

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 might be inherited or acquired due to an underlying medical condition or a medication.

Inherited long QT syndrome

At least 17 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 cases, while mutations in the other 14 minor genes contribute less than 5 percent of long QT syndrome cases. About 20 percent of people who definitely have long QT syndrome have a negative genetic test result.

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.
  • 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 have long QT syndrome and are also born deaf because they inherited genetic variants from each parent.

Additionally, scientists have been investigating a possible link between sudden infant death syndrome (SIDS) and long QT syndrome and have discovered that approximately five to 10 percent of babies affected by SIDS had a genetic defect or mutation for long QT syndrome.

Acquired long QT syndrome

Acquired long QT syndrome can be caused by certain medications or medical conditions. More than 75 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
  • Certain antidepressant and antipsychotic medications
  • Some antihistamines
  • Diuretics
  • Medications used to maintain normal heart rhythms (antiarrhythmic medications)
  • Cholesterol-lowering medications
  • Certain diabetes medications

People who develop drug-induced long QT syndrome might 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 who may have a higher risk of inherited or acquired long QT syndrome may 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
  • First-degree relatives of people with known long QT syndrome
  • People taking medications known to cause prolonged QT intervals
  • People with low potassium, magnesium or calcium blood levels — such as those with the eating disorder anorexia nervosa

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

Sometimes, prolonged QT intervals in people with long QT syndrome never cause problems. However, physical or emotional stress might "trip up" a heart susceptible to prolonged QT intervals. This can cause the heart's rhythm to spin out of control, triggering life-threatening, irregular heart rhythms (arrhythmias) including:

  • Torsades de pointes — 'twisting of the points.' This arrhythmia is characterized by your heart's two lower chambers (ventricles) beating 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 suddenly and, often, without any warning.

    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.

  • Ventricular fibrillation. This condition causes the ventricles to beat so fast that your heart quivers and effectively 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 now known that long QT syndrome might explain some cases of sudden death in young people who otherwise appear healthy.

If you develop signs and symptoms common to long QT syndrome, contact your doctor. After an initial exam, it's likely that the doctor will refer you to a doctor trained in diagnosing and treating heart conditions (cardiologist), a doctor trained in heart rhythm conditions (electrophysiologist) or a cardiologist who specializes in sudden death predisposing genetic heart conditions (genetic cardiologist).

Here's some information to help you prepare for your appointment, and what to expect from your doctor.

What you can do

  • Write down any signs and symptoms you've had, and for how long.
  • Write down your key medical information, including any other health conditions and the names of all of your medications. It will also be important to share any family history of heart disease or sudden death with your doctor.
  • Find a family member or friend who can come with you to the appointment, if possible. Someone who accompanies you can help remember what the doctor says.
  • Write down the questions you want to be sure to ask your doctor.

Questions to ask the doctor at your initial appointment include:

  • What is likely causing my signs and symptoms?
  • Are there any other possible causes for these signs and symptoms?
  • What tests are needed?
  • Should I consult a specialist?

Questions to ask if you're referred to a cardiologist or electrophysiologist include:

  • Do I have long QT syndrome? What type?
  • What is my risk of complications from this condition?
  • What treatment approach do you recommend?
  • If the first treatment doesn't work, what will you recommend next?
  • If you're recommending medications, what are the possible side effects?
  • If you're recommending surgery, what type of procedure is most likely to be effective in my case? Why?
  • What should I expect from my recovery and rehabilitation after surgery?
  • Will I need frequent exams and lifelong treatment for this condition?
  • What emergency signs and symptoms of long QT syndrome should I be aware of?
  • Should I tell my friends, teachers and co-workers that I have this condition?
  • What activity restrictions will I need to follow?
  • Could any dietary changes help me manage this condition?
  • What medicines should I avoid?
  • What is my long-term outlook with treatment?
  • Will it be safe for me to become pregnant in the future?
  • What is the risk that my future children would have this defect?
  • Should I meet with a genetic counselor?

In addition to the questions that you've prepared ahead of time, don't hesitate to ask other questions during your appointment if you don't understand something.

What to expect from your doctor

A doctor who sees you for possible long QT syndrome might ask a number of questions, including:

  • What are your symptoms?
  • When did you first begin experiencing symptoms?
  • Have your symptoms gotten worse over time?
  • Do strong emotions trigger your symptoms, such as excitement, anger or surprise?
  • Does exercise bring on your symptoms?
  • Does being startled — such as by a doorbell or phone ringing — trigger your symptoms?
  • Do your symptoms include feeling lightheaded or dizzy?
  • Have you ever fainted?
  • Have you ever had a seizure?
  • Do your symptoms include a fluttering sensation in your chest?
  • Do you gasp in your sleep that you're aware of?
  • Have you been diagnosed with any other medical conditions?
  • Are you aware of any history of heart conditions in your family?
  • Have any first-degree relatives — parent, sibling or child — ever died unexpectedly, such as from drowning, or died suddenly without explanation?
  • What medications are you currently taking, including over-the-counter and prescription drugs as well as vitamins and supplements?
  • Have you ever used recreational drugs? If so, which ones?
  • What is your usual daily diet?
  • Do you use caffeine? How much?
  • Do you have any children? Are you planning any future pregnancies?

What you can do in the meantime

While you wait for your appointment, check with your family members to find out if any first-degree relatives (children, siblings, parents), second-degree relatives (aunts, uncles, grandparents), third-degree relatives (great aunts, great uncles, cousins) or any other known relatives have been diagnosed with heart disease or have died suddenly.

Having a first-degree relative who died from an unexpected cause — such as from SIDS, from drowning or while driving — is an important clue for your doctor. And in general, knowing as much as possible about your family's health history will help your doctor determine the next steps for your diagnosis and treatment.

A nonprofit advocacy organization called the Sudden Arrhythmia Death Syndromes (SADS) Foundation can help you prepare and understand your family history as it relates to a possible diagnosis of LQTS.

If exercise makes your symptoms worse, avoid exerting yourself physically until you've been seen by your doctor.

To diagnose long QT syndrome, your doctor will review your symptoms, review your medical and family history, and conduct a physical examination. If your doctor suspects that you have long QT syndrome, you might need several tests to confirm the diagnosis. These include:

  • Electrocardiogram (ECG). During an ECG, doctors attach sensors (electrodes) that can detect the electrical activity of your heart to your chest. An ECG measures the timing and duration of each electrical phase in your heartbeat.

    You might have this test while at rest or during an exercise stress test, in which doctors monitor your heart activity as you exercise on a treadmill or a stationary bicycle. Your doctor may also suggest your family members have ECGs.

  • Holter monitor. This portable ECG device can be worn for a day or more to record your heart's activity as you go about your routine.
  • Event monitor. This portable ECG device is attached to your body and is intended to monitor your heart activity over a few weeks to a few months. When you have symptoms, you press a button. This allows your doctor to check your heart rhythm at the time of your symptoms.

In some people with suspected long QT syndrome, the ECG doesn't show a visibly lengthened QT interval. Other testing may be necessary to diagnose long QT syndrome, such as:

  • A nonexercise (medication) stress test. This ECG test is done while you're given a medication such as epinephrine (Adrenalin) that stimulates your heart in a way similar to exercise. In this test, doctors monitor the effects of the medication on the way your heart recharges.

    This test can help doctors to diagnose people with suspected long QT syndrome and may help determine which genes are associated with the condition. It may also be used to diagnose people with long QT syndrome who have a gene associated with long QT syndrome but who have a normal QT interval (recharging time) at rest.

  • Genetic testing. A genetic test for long QT syndrome is available and may be covered by some private and governmental insurance plans. Genetic tests for long QT syndrome can generally find the genetic cause for about 3 out of every 4 cases of long QT syndrome. However, genetic tests can't detect all cases of long QT syndrome.

    If your genetic cause of long QT syndrome is discovered through a positive genetic test, then your doctor may recommend that your family members be tested to determine whether they inherited the same genetic mutation.

  • A second opinion. You might want to seek a second opinion before proceeding with treatment if your doctor diagnoses you with long QT syndrome. Studies have found that people can sometimes be misdiagnosed as having long QT syndrome when it's not actually present.

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. Your doctor will discuss with you the most appropriate treatment options for your condition based on your symptoms, your type of long QT syndrome, and your risk of fainting or sudden cardiac arrest.

For acquired long QT syndrome, treating the cause of the condition may eliminate it. Doctors will also treat heart rhythm disorders (arrhythmias) as needed.

If acquired long QT syndrome is due to certain medications, your doctor may recommend that you stop taking the medication causing the condition and switch medications in order to treat the condition. Some people might need additional treatment.


Medications used to treat long QT syndrome may include:

  • Beta blockers. Examples of these heart drugs include nadolol (Corgard) and propranolol (Inderal LA, Innopran XL). These drugs slow the heart rate and make the dangerous rhythm associated with long QT syndrome less likely. Beta blockers work by blunting the way a long QT syndrome-affected heart reacts to adrenaline, as it can beat faster in times of stress, fear or exertion.
  • Mexiletine. In people with a form of long QT syndrome called LQT3, taking this anti-arrhythmic drug in combination with beta blockers might help shorten the QT interval.
  • Potassium. Potassium is a mineral derived from your diet that's important for the health of your heart's electrical system. For certain forms of long QT syndrome, potassium supplements might improve the heart's recharging system.
  • Fish oil. Supplementation with heart-healthy fish oil (omega-3 fatty acid) or eating fish high in omega-3 fatty acids might help decrease the risk of abnormal heart rhythms. Consult your doctor before starting fish oil or any other supplements or medications.

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

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 might need to take a medication such as a beta blocker indefinitely.

Medical devices and surgical procedures

Depending on your condition, your doctor might consider other treatments for you, including:

  • A pacemaker or implantable cardioverter-defibrillator (ICD). These devices, which are implanted under the skin of your chest, can stop a potentially fatal arrhythmia.

    An ICD continuously monitors your heartbeat. If it detects an abnormal heart rhythm, it delivers electrical shocks to reset the heart to a normal heart rhythm.

    If a pacemaker detects a heart rate that's abnormal, it emits electric impulses that stimulate your heart to beat at a normal rate.

  • Left cardiac sympathetic denervation surgery. In this procedure, specific nerves in your chest are surgically removed. These nerves are part of the body's sympathetic nervous system, which controls automatic functions in the body including regulation of heart rhythm. Left cardiac sympathetic denervation surgery significantly reduces the risk of sudden death.

    This surgery is generally reserved for people considered at high risk of sudden death, people who don't tolerate their medications or have a fainting spell despite their medications, and people who have an implanted ICD and are experiencing ICD shocks. Left cardiac sympathetic denervation surgery might significantly reduce the frequency of such appropriate ICD shocks.

Lifestyle changes

In addition to medications or surgery, your doctor might recommend lifestyle changes to reduce your chances of a long QT syndrome-related fainting spell or sudden cardiac arrest. These could include:

  • Avoiding medications that could cause prolonged QT intervals
  • Staying well-hydrated during illnesses that are causing vomiting or diarrhea
  • Lowering your temperature if a fever occurs
  • Reducing loud or startling noises
  • Staying away from situations that could make you excited or angry
  • Avoiding strenuous exercise or contact sports, or have a safety plan in place if you'll be continuing competitive sports

Work with your doctor to balance these lifestyle recommendations against the clear, heart-healthy benefits of an active lifestyle. In some circumstances, it might be possible to stay fully active in sports, including competitive sports, after carefully reviewing the risks and benefits with your doctor.

If your symptoms are mild or don't occur very often, your doctor might recommend only simple preventive measures or lifestyle changes for your condition, and he or she might not prescribe any daily medications for you.

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 might 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 might be dangerous and isn't recommended for some people with long QT syndrome. However, others might have a lower risk of complications and may be able to continue strenuous exercise and even 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, such as feeling like you may faint.
  • 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 providers 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 if it ever becomes necessary.

    In some situations, possession of or rapid access to an automatic external defibrillator (AED) might be appropriate.

  • Control startling events as much as possible. Turn down the volume on doorbells and turn off the telephone ringer or your cellphone at night.
  • Visit your doctor. Your cardiologist will likely recommend that you have regular follow-up appointments with him or her. Let your doctor know if you have symptoms of long QT syndrome or any changes in your condition. Your doctor may make changes to your treatment plan or suggest additional treatments for you.

Sexual intercourse doesn't appear to increase the risk of long QT syndrome. Pregnancy and delivery aren't associated with an increased risk of symptoms in women with long QT syndrome.

Still, 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, especially a form called LQT2, are at increased risk during the postpartum period and need careful monitoring.

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 might 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.

If you have inherited long QT syndrome, be careful about which medications you take. Some medications — including certain appetite suppressants, decongestants and common antibiotics — might trigger dangerous heart rhythms. Ask your doctor what you can and can't take safely. Illegal 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 excessive vomiting and diarrhea. Such illnesses could trigger an episode of long QT syndrome in people at risk. Your doctor might advise you not to take some drugs, such as diuretics, that lower blood-potassium levels.

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.

Oct. 27, 2015