To diagnose long QT syndrome, your doctor will perform a physical exam and ask questions about your or your child's symptoms and medical and family history. Your doctor will use a stethoscope to listen to your heart.

An electrocardiogram is the most common test used to diagnose long QT syndrome.

Electrocardiogram (ECG or EKG)

An electrocardiogram is a quick and painless test that records the electrical signals in your heart. You might have an ECG while at rest or while exercising on a treadmill or stationary bicycle. If you cannot safely exercise, you may be given a medication such as epinephrine (Adrenalin) that stimulates your heart in a way similar to exercise.

During an ECG, sticky patches (electrodes) are placed on your chest to record your heart's electrical signals, which cause your heart to beat. The signals are shown as waves on an attached computer monitor or printer.

An ECG can tell if you are having a prolonged QT interval. The test labels the heart's electrical signals as five waves using the letters P, Q, R, S and T. The waves labeled Q through T show the 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 is the QT interval. That's the time it takes for your heart to contract and refill with blood before it beats again.

What's normal for you depends on your age, your sex and your individual heart rate. Your doctor will consider this information. If the interval takes longer than normal to occur, it's called a prolonged QT interval.

Remote ECG monitoring

If your long QT symptoms tend to come and go, they may not be captured during a standard ECG recording. In this case your doctor may recommend remote or continuous ECG monitoring. There are several different types.

  • Holter monitor. A Holter monitor is a small, wearable device that records a continuous ECG, usually for 24 to 48 hours.
  • Event monitor. This portable device is similar to a Holter monitor, but it records only at certain times for a few minutes at a time. You can wear it longer than a Holter monitor, typically 30 days. You generally push a button when you feel symptoms. Some devices automatically record when an abnormal rhythm is detected.

Genetic testing

A genetic test for long QT syndrome is available and recommended by many doctors to confirm the diagnosis. Check with your insurer to see if it is covered.

It's important to understand that genetic tests for long QT syndrome can't detect all inherited cases of long QT syndrome. It's recommended that families speak to a genetic counselor before and after testing.

If you have a positive genetic test for long QT syndrome, your doctor may recommend that other family members also be tested to determine whether they inherited the same gene.


Treatment for long QT syndrome involves lifestyle changes, medications, and possibly surgery or other procedures.

The goal of treatment is to prevent erratic heartbeats and sudden death. Your doctor will discuss with you the most appropriate treatment options based on your symptoms and your type of long QT syndrome. Your doctor might suggest treatment even if you don't often have signs or symptoms.

If you have drug-induced long QT syndrome, stopping the medication causing your symptoms may be all that is needed to treat the condition. Your doctor can tell you how to safely do so.

For other cases of acquired long QT syndrome, treating the underlying condition is necessary. Treatment varies but may include magnesium or other fluids given by IV to correct electrolyte imbalances.


Medications won't cure long QT syndrome, but they can help protect against possible life-threatening heart rhythm changes.

Medications used to treat long QT syndrome may include:

  • Beta blockers. These heart drugs are standard therapy for most patients with long QT syndrome. They slow the heart rate and make long QT episodes less likely. Beta blockers used to treat long QT syndrome include nadolol (Corgard) and propranolol (Inderal LA, InnoPran XL).
  • Mexiletine. Taking this heart rhythm drug in combination with a beta blocker might help shorten the QT interval and reduce your risk of fainting, seizure or sudden death.

Always take the medications your doctor prescribes as directed.

Surgery or other procedures

Depending on your symptoms, your doctor might consider other long QT syndrome treatments for you, including:

  • Left cardiac sympathetic denervation (LCSD) 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 control your heart rhythm.

    LCSD is generally reserved for people with long QT and persistent heart rhythm problems who are at high risk of symptoms and cannot take or tolerate beta blockers. It doesn't cure long QT syndrome, but it does help reduce the risk of sudden death.

  • Implantable cardioverter-defibrillator (ICD). An ICD is implanted under the skin of your chest and continuously monitors your heartbeat. It can stop a potentially life-threatening arrhythmia. When an ICD detects an abnormal heart rhythm, it delivers electrical shocks to reset the heart back to normal.

    Most people with long QT syndrome do not need an ICD. However, the procedure may be done in certain athletes to allow return to competitive sports. The decision to implant an ICD, especially in children, needs to be carefully considered. Implanting an ICD is a major procedure and can result in inappropriate shocks and other complications.

Clinical trials

Explore Mayo Clinic studies testing new treatments, interventions and tests as a means to prevent, detect, treat or manage this condition.

Lifestyle and home remedies

In addition to recommending medications or surgery, your doctor might suggest lifestyle changes to reduce your chances of a long QT syndrome-related fainting spell or sudden cardiac death.

  • Know which sports are safe. It may be possible to stay fully active in sports, including competitive sports, after carefully reviewing the risks and benefits with your doctor. In general, people with long QT syndrome should never swim alone. Recreational activities are likely to be OK as long as you take a buddy along in case you have a fainting episode.
  • Do a sound check. Turn down the volume on doorbells and other devices (such as telephones) that may startle you, especially during sleep.
  • Keep emotions in check. Being very excited, angry or surprised can trigger heartbeat changes in some people with long QT syndrome.
  • Check your meds. Avoid drugs that could cause prolonged QT intervals. If you're not sure, ask your doctor. It's a good idea to let you doctor know about all the medications and supplements you take, even those you buy without a prescription.
  • Get regular checkups. During your appointment, let your doctor know if you have any changes in your symptoms or condition. Your doctor may update your treatment plan or suggest additional treatments for you.

Coping and support

Worrying about possible dangerous heart rhythms associated with long QT syndrome can cause stress for you and your loved ones. Take steps to help your loved ones better understand how to support you and care for you in an emergency.

  • Tell other people. Make family, friends, teachers, neighbors and anyone else who has regular contact with you aware of your heart condition and your symptoms. Wear a medical alert identification to notify others of your condition.
  • Have an emergency plan. Family members may want to learn cardiopulmonary resuscitation 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.
  • Seek support or counseling. Some people find it helpful to join a support group, where they can share their experiences and feelings with other people and families who are familiar with the condition. Families with inherited long QT syndrome might also find it helpful to talk to a genetics counselor.

Preparing for your appointment

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).

Here's some information to help you prepare for your appointment and know 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? Which 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?
  • Are you aware of any gasping in your sleep?
  • 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 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 you have a family history of long QT syndrome or unexplained death.

Having a first-degree relative who died from an unexpected cause — such as sudden infant death syndrome (SIDS), drowning or other accident — 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.

Long QT syndrome care at Mayo Clinic

June 16, 2020
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