To diagnose long QT syndrome, a health care provider does a physical exam and asks questions about your symptoms and medical and family history. The health care provider uses a stethoscope to listen to your heart. If your provider thinks you have an irregular heartbeat, tests can be done to check the heart's rhythm.
Tests are done to confirm a diagnosis of long QT syndrome or check for other conditions that may affect the heart's rhythm or raise the risk of irregular heartbeats.
Electrocardiogram (ECG or EKG)
Prolonged QT interval
A prolonged QT interval is an irregular heart rhythm that can be seen on an electrocardiogram. It reflects a disturbance in how the heart's bottom chambers (ventricles) send signals. In a prolonged QT interval, it takes longer than usual for the heart to recharge between beats.
This is the most common test used to diagnose long QT syndrome. An ECG is a quick and painless test that records the electrical signals in the heart. During an ECG, sensors (electrodes) are attached to the chest and sometimes to the arms or legs. An ECG measures the timing and duration of each electrical phase in the heartbeat. The signals are shown as waves on an attached computer monitor or printer.
- An ECG labels the heart's electrical signals as five waves using the letters P, Q, R, S and T.
- Waves Q through T show the electrical activity in the heart's lower chambers (ventricles).
- The QT interval is the space between the start of the Q wave and the end of the T wave. The interval is the time it takes for the heart to contract and refill with blood before it beats again. If the interval takes longer than usual to occur, it's called a prolonged QT interval.
An optimal QT interval depends on your age, your sex and your individual heart rate.
If long QT symptoms are infrequent, they may not be seen on a standard ECG. If this happens, remote ECG monitoring may be recommended. There are several different types.
- Holter monitor. Your health care provider may recommend this portable ECG device to monitor your heartbeat at home. It's worn for a day or more to record the heart's activity during daily activities.
- Event monitor. This portable ECG device is worn for up to 30 days or until you have an arrhythmia or symptoms. You typically press a button when symptoms occur. Some devices automatically record when an irregular heartbeat (arrhythmia) is detected.
Some personal devices, such as smartwatches, offer electrocardiogram monitoring. Ask your health care provider if this is an option for you.
Exercise stress test
This type of test often involves walking on a treadmill or riding a stationary bike while the heart is monitored with an ECG. Exercise tests help reveal how the heart responds to physical activity. If you're unable to exercise, you may be given a medication that stimulates the heart in a way like exercise.
A genetic test for long QT syndrome is available to confirm the diagnosis. Check with your insurer to see if it is covered.
If you have a positive genetic test for long QT syndrome, your health care provider may recommend that other family members also be tested to determine whether they inherited the same gene.
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.
Treatment for long QT syndrome (LQTS) may include lifestyle changes, medications, and surgery or other procedures.
The goal of LQTS treatment is to prevent erratic heartbeats and sudden death. Your health care provider will discuss with you the most appropriate treatment options based on your symptoms and your type of long QT syndrome. You may need treatment even if you don't often have symptoms.
If you have drug-induced long QT syndrome, stopping the medication causing the symptoms may be all that's needed to treat the condition. Your health care provider can tell you how to safely do so.
For other types 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 with a beta blocker might help shorten the QT interval and reduce the risk of fainting, seizure or sudden death.
Always take medications as directed.
Surgery or other procedures
Some people with long QT syndrome need surgery to control the heartbeat. Surgery or other procedures used to treat LQTS may include:
- Left cardiac sympathetic denervation (LCSD) surgery. LCSD surgery is usually only recommended for people with long QT syndrome and persistent heart rhythm problems who can't take or tolerate beta blockers. It doesn't cure long QT syndrome, but it does help reduce the risk of sudden death. In this procedure, surgeons remove specific nerves along the left side of the spine in the chest. These nerves are part of the body's sympathetic nervous system, which helps control the heart rhythm.
Implantable cardioverter-defibrillator (ICD). An ICD is a battery-powered unit that's implanted under the skin near the collarbone — similar to a pacemaker. The ICD continuously monitors the heart rhythm. If the device detects an irregular heartbeat, it sends out shocks to reset the heart's rhythm. It can stop a potentially life-threatening arrhythmia.
Most people with long QT syndrome don't need an ICD. However, an ICD may be recommended for 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.
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
Lifestyle changes may be recommended to reduce the 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 health care provider. In general, people with long QT syndrome should never swim alone. Recreational activities are likely to be OK if you take a buddy along in case you have a fainting episode.
- Check for startling sounds. Turn down the volume on doorbells and other devices (such as telephones) that may startle you, especially during sleep.
- Manage emotions. Being very excited, angry or surprised can trigger heartbeat changes in some people with long QT syndrome.
- Check your medicines. Avoid drugs that could cause prolonged QT intervals. If you're not sure, ask your health care provider. It's a good idea to let your provider know about all the medications and supplements you take, even those you buy without a prescription.
- Get regular health checkups. If you have changes in your symptoms or condition, your health care provider may update your treatment plan or suggest additional treatments.
Coping and support
Worrying about possible dangerous heart rhythms associated with long QT syndrome (LQTS) may cause stress for you and your loved ones. It might be helpful to take steps to help your loved ones better understand how to support you and care for you during an LQTS episode.
- Tell other people you have LQTS. 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 (CPR) so they help if you ever need it. It may be appropriate to have or be able to rapidly access an automated external defibrillator (AED).
- 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 who are familiar with long QT syndrome. Families with inherited long QT syndrome might also find it helpful to talk to a genetic counselor.
Preparing for your appointment
If you have pounding, fast or irregular heartbeats, make an appointment with your health care provider. You may be referred to a health care provider with special training in heart conditions. Providers that help care for people with long QT syndrome include:
- Doctors trained in diagnosing and treating heart conditions (cardiologists)
- Doctor trained in heart rhythm conditions (electrophysiologists)
- Doctors who specialize in genetic heart conditions (genetic cardiologists)
Here's some information to help you prepare for your appointment and know what to expect from your health care provider.
What you can do
- Write down any symptoms you've had, and for how long. Include those that may seem unrelated to long QT syndrome.
- Write down important medical information, including any other health conditions you have and the names and doses of any medications that you take. It's also important to share any family history of irregular heartbeats (arrhythmias) or sudden death with your health care provider.
- Write down the questions you want to be sure to ask your health care provider.
Questions to ask the health care provider at your first appointment include:
- What is likely causing my symptoms?
- Are there any other possible causes for these symptoms?
- What tests do I need?
- 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 health care provider 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 symptoms of long QT syndrome should I be aware of?
- What activity restrictions will I need to follow?
- Could diet 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 will have long QT syndrome?
- How can genetic counseling help my family?
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 health care provider who sees you for possible long QT syndrome might ask several questions, including:
- What are your symptoms?
- When did the symptoms start?
- Have the symptoms gotten worse over time?
- Do strong emotions — such as anger, excitement or surprise — trigger your symptoms?
- Does exercise cause 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 you have any other medical conditions?
- Are you aware of any history of heart conditions in your family?
- Has a parent, brother, sister or child ever died unexpectedly, such as by drowning, or died suddenly without explanation?
- What medications are you currently taking, including those bought without a prescription as well as vitamins and supplements?
- Have you ever used recreational drugs? If so, which ones?
- Do you use caffeine? How much?
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.
Tell your health care provider if you have a first-degree relative — such as a parent, brother or sister — who died of an unexpected cause such as sudden infant death syndrome (SIDS), drowning or other accident. In general, knowing as much as possible about your family's health history helps your health care provider determine the next steps for your diagnosis and treatment.