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 have a genetic mutation that puts you at risk of being born with congenital long QT syndrome. In addition, certain medications, imbalances of the body's salts and minerals (electrolyte abnormalities), and medical conditions might cause acquired long QT syndrome.

Long QT syndrome is treatable. You might need to take medications to prevent an erratic heart rhythm. In some cases, treatment for long QT syndrome involves surgery or an implantable device.

You'll also need to avoid certain medications that could trigger your long QT syndrome. After treatment, you likely can live and thrive, even with this condition. You may be able to continue being active in recreational — and even competitive — sports.

Many people who have long QT syndrome don't have any signs or symptoms. You might be aware of your condition only because of:

  • Results of an electrocardiogram (ECG) done for an unrelated reason
  • A family history of long QT syndrome
  • Genetic testing results

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

    You may lose consciousness without warning, for instance from being startled by a ringing telephone. If you have a normal fainting spell, you usually will have a warning sign first, such as lightheadedness, heart palpitations, irregular heartbeat, weakness or blurred vision. However, a fainting spell from long QT syndrome can occur with little to no warning.

  • Seizures. If the heart continues to beat erratically, the brain will eventually not get enough oxygen, which can cause seizures.
  • Sudden death. Generally, the heart returns to its normal rhythm. If this doesn't happen by itself, or if an external defibrillator isn't used in time to convert the rhythm back to normal, sudden death will occur.

Signs and symptoms of inherited or congenital long QT syndrome might start as a fetus, during the first weeks to months after birth, 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, especially if the medication is known to prolong the QT interval.

Because long QT syndrome can occur in families, also tell your doctor that you'd like 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).

Normally 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 that 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, 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.

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, they may be 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 found 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 minor genes contribute a small percent of long QT syndrome cases.

About 20 percent of people who definitely have congenital long QT syndrome have a negative genetic test result. On the other hand, among families with genetically established long QT syndrome, between 10 percent and 37 percent of the relatives with a positive long QT syndrome genetic test have a normal QT interval.

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 parent.
  • Jervell and Lange-Nielsen syndrome. This rare form usually occurs earlier and is more severe. In this syndrome, children inherit genetic variants from both parents. They have long QT syndrome and also are born deaf.

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, electrolyte abnormalities such as low body potassium (hypokalemia) or medical conditions. More than 100 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)
  • Some anti-nausea medications

People who develop drug-induced long QT syndrome might also have some subtle genetic defects in their hearts. These defects make them more likely to have disruptions in their heart rhythm from certain medications.

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

Inherited 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.

Most of the time, prolonged QT intervals in people with long QT syndrome never cause problems. However, physical or emotional stress might "trip up" a heart that is sensitive 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.' In this arrhythmia, your heart's two lower chambers (ventricles) beat fast and chaotically, making the waves on an ECG monitor look twisted. Less blood is pumped out from your heart, so less blood 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 and you regain consciousness on your own. However, if a torsades de pointes episode lasts longer, it can result in a sudden fainting spell followed by a full-body seizure. If the dangerous rhythm does not correct itself, then a life-threatening arrhythmia called ventricular fibrillation follows.

  • Ventricular fibrillation. This condition causes the ventricles to beat so fast that your heart quivers and ceases pumping blood. Unless your heart is shocked back into a normal rhythm by a defibrillator, ventricular fibrillation can lead to brain damage and sudden 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 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, especially if you have a lot of vomiting and diarrhea. Such illnesses could trigger an episode of long QT syndrome. Your doctor might advise you not to take some drugs, such as diuretics, that lower blood-potassium levels.

Some people — especially older adults with long QT syndrome who haven't had signs or symptoms of the condition in decades — may not need any treatment other than preventive measures.

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

  • Electrocardiogram (ECG). During an ECG, doctors attach sensors to your chest (electrodes) that can detect the electrical activity of your heart. 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 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 an abnormally prolonged QT interval. You may need other tests, such as:

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

    This test can help doctors 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 inherited 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, your doctor may recommend that your family members also 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. People can sometimes be misdiagnosed as having long QT syndrome when it's not actually present.

Treatment for inherited long QT syndrome involves some simple preventive measures. It can also involve medications, as well as left cardiac sympathetic denervation surgery or implanting medical devices such as a defibrillator (ICD), or both.

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 you are diagnosed with acquired long QT syndrome due to certain medications, your doctor may recommend that you stop taking the medication causing the condition and switching medications. Some people might need additional treatment.


Medications used to treat long QT syndrome may include:

  • Beta blockers. These heart drugs include nadolol (Corgard) and propranolol (Inderal LA, InnoPran XL). They slow the heart rate and make the rhythm associated with long QT syndrome less likely. Beta blockers work by blunting the way your heart reacts to adrenaline.
  • Mexiletine. Taking this anti-arrhythmic drug in combination with beta blockers might help shorten the QT interval and decrease the likelihood of a long QT syndrome-triggered faint, seizure or sudden death.

    This medication is often used for the third-most common subtype of inherited long QT syndrome, LQT3. However, it may also be used for the two most common subtypes, LQT1 and LQT2.

  • Spironolactone and potassium. For certain forms of long QT syndrome, spironolactone (Aldactone), a medication used to help the body hold on to potassium, or potassium supplements, or both, might improve the heart's recharging system.
  • Fish oil. In general, current evidence does not support supplementation with heart-healthy fish oil (omega-3 fatty acid) or eating fish high in omega-3 fatty acids to decrease the risk of cardiac events or death from abnormal heart rhythms. However, if you have inherited long QT syndrome, fish oil may be a reasonable complementary alternative medication to take in addition to other therapies. Talk to 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 often experience signs or symptoms.

If you do need treatment, take the medications your doctor prescribes as directed. While medications won't cure the condition, they provide some protection against possibly fatal disruptions of your heart rhythm. You might need to take a medication such as a beta blocker indefinitely.

Surgical procedures

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

  • Left cardiac sympathetic denervation surgery. In this procedure, surgeons remove specific nerves along the left side of your spine in your chest. These nerves are part of the body's sympathetic nervous system, which helps regulate heart rhythm. The surgery significantly reduces the risk of sudden death.

    This surgery is generally reserved for people who are considered at high risk of sudden death and are experiencing appropriate ICD shocks, people who are continuing to experience fainting or seizures while taking their medications, or people unable to tolerate their medications because of side effects.

  • Implantable cardioverter-defibrillator (ICD). This device, which is 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 rhythm.

    Implanting an ICD is a major procedure and can result in inappropriate shocks and other complications. Therefore, the decision to implant an ICD, especially in children, needs to be carefully considered.

    Most people with inherited long QT syndrome do not need an ICD. Importantly, an ICD should not be implanted solely because of the tragic occurrence of a long QT syndrome-triggered sudden death in a relative.

Potential future treatments

A combination of advances in the field of genetics, computerized clinical decision support systems that alert doctors to drug interactions, and handheld or wearable monitors may help improve treatment for people with both inherited and acquired long QT syndrome.

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
  • Getting plenty of liquids during illnesses that are causing vomiting or diarrhea
  • Lowering your temperature if a fever occurs
  • Reducing your exposure to 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 continue in competitive sports

Work with your doctor to balance these lifestyle recommendations against the clear, heart-healthy benefits of an active lifestyle. It may 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, 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, including:

  • Don't overexert yourself. You might not need 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 in detail.

  • 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 a medical alert identification to notify health care providers of your condition.
  • Have plans in case of an emergency cardiac event. Family members may want to learn cardiopulmonary resuscitation (CPR) so they can provide immediate resuscitation if you ever need it. In some situations, it might be appropriate to have or be able to rapidly access an automatic external defibrillator (AED).

    However, if your inherited long QT syndrome has been evaluated and treated carefully, you are generally unlikely to ever need CPR or an AED.

  • 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, if you have inherited long QT syndrome, your doctor will want to monitor you closely both during your pregnancy and after. Women with long QT syndrome, especially a form called LQT2, are at increased risk during the period following delivery 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 be stressful for you and your family.

Families with inherited long QT syndrome might find it helpful to talk to a cardiologist with expertise in long QT syndrome, a genetics counselor and a therapist, as well as other families with the condition.

If you develop signs and symptoms of long QT syndrome, contact your doctor. After an initial exam, your doctor likely 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 genetic heart conditions (genetic cardiologist) that may predispose people to sudden death.

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?

Questions to ask if your doctor recommends surgery include:

  • What type of procedure is most likely to be effective in my case and why?
  • Where should I have my surgery performed?
  • Should I be referred to a long QT syndrome center of excellence?
  • What should I expect from my recovery and rehabilitation after surgery?

Additional questions include:

  • 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. 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 exercising until you see your doctor.

Last Updated: 03-21-2018
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