A Guide to Long QT Syndrome (LQTS)

Medically Reviewed By Dr. Payal Kohli, M.D., FACC
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Long QT syndrome (LQTS) is a conduction disorder of the heart. It affects the electrical activity that makes the heart beat. People with LQTS may or may not have symptoms. LQTS can lead to life threatening heart arrhythmias and death. Medicines and implantable devices can help control LQTS.

This article describes LQTS, including the types, symptoms, causes, and treatments.

What is long QT syndrome?

Illustration of heart beat QT interval
QT Interval Illustrated

LQTS is a disorder in the electrical condition of the heart. The term “QT” refers to the readout on an electrocardiogram (ECG).

There are five waves that make up a heartbeat on an ECG: P, Q, R, S, and T. The interval between Q and T represents the resetting activity of the ventricles after the heart beats. (These lower chambers pump blood out of the heart.)

In LQTS, the QT interval is longer than normal. This can cause fatal arrhythmias and cardiac events, such as cardiac arrest. LQTS is rare.

What are the types of long QT syndrome?

There are two main types of LQTS: congenital and acquired. Each of these involves ion channels on the surface of heart muscle cells. These channels allow sodium, potassium, and calcium to go in and out of the cells. This is what generates the electrical activity that makes the heart beat. 

In congenital LQTS, people are born with mutations in the ion channels. This can cause them to have too few ion channels or to have ion channels that do not work right. There are at least 15 different genes that can result in LQTS.

Acquired LQTS develops later in life. It is usually the result of drugs that affect the ion channels or electrolyte imbalances.

What are the symptoms of long QT syndrome?

Fainting is the most common symptom of LQTS. This tends to occur during exercise or times of physical or emotional stress. With one type of congenital LQTS, fainting often occurs during swimming or after diving into water. However, some people do not have any symptoms.

Symptoms can also include near fainting and seizures. In up to 15% of cases, cardiac arrest or death is the first sign of LQTS. Cardiac arrest occurs when the heart suddenly stops beating. 

In congenital LQTS, other signs and symptoms can occur that do not affect the heart. These include:

When to see a doctor

See a doctor if you have unexplained fainting, near fainting, near drowning, or seizures. You should also see a doctor if you have a first-degree relative with these symptoms, or who has experienced drowning, sudden death, or LQTS. Also seek medical treatment if you have been told that you have a long QT on an ECG.

What causes long QT syndrome?

A long QT interval occurs when something disturbs the normal flow of ions into and out of heart muscle cells. Too many positive ions build up inside the cells. This prolongs the time it takes for the ventricles to contract and relax. 

In congenital LQTS, the cause of the ion flow disruption is genetic. Gene mutations cause the ion channels to malfunction.

In acquired LQTS, electrolyte imbalances and certain medicines can disrupt the proper flow of ions. Medicines that can cause LQTS include some:

  • antiarrhythmics, such as amiodarone and sotalol
  • antibiotics, such as azithromycin (Zithromax), ciprofloxacin (Cipro), and erythromycin
  • antidepressants, such as amitriptyline (Elavil) and fluoxetine (Prozac)
  • antipsychotics, such as haloperidol (Haldol) and olanzapine (Zyprexa)

Several drugs are no longer on the market due to their potential to cause LQTS and dangerous arrhythmias. Examples include terfenadine (Seldane) and cisapride (Propulsid).

Who is at risk for long QT syndrome?

There are several risk factors for LQTS, including:

  • family history of LQTS, sudden death, unexplained seizures, fainting, near fainting, drowning, or near drowning
  • female biological sex
  • heart conditions, including cardiomyopathy and congenital heart defects
  • medical conditions that affect electrolytes, such as eating disorders, thyroid disease, and dehydration

How do doctors diagnose long QT syndrome?

To diagnose LQTS, your doctor will take a medical history and perform an exam. Your doctor will need to learn about your symptoms — if you have any — as an important part of this process. If your family history suggests LQTS, your doctor can order genetic testing to screen you for it.

To find LQTS, your doctor can order an ECG. This painless test measures the electrical activity of your heart.

LQTS shows up as an abnormally long interval between the Q wave and T wave of your heartbeat. This QT interval can vary depending on your normal heart rate. The QT interval will be shorter with a higher heart rate and longer for a lower heart rate. This is QT corrected for heart rate, or QTc.

In males, a prolonged QTc is longer than 440 milliseconds (ms). In females, it is longer than 460 ms. 

Once your doctor diagnoses LQTS, more testing may be necessary to find the cause. This may involve blood tests to check electrolyte levels and thyroid hormone levels.

What are the treatments for long QT syndrome?

The goal of treating LQTS is to prevent symptoms, such as fainting, and dangerous arrhythmias. The treatment you need will depend on how long the QT interval is. The longer the interval, the higher the risk of life threatening heart rhythm problems. 

Treatment options for LQTS include:

In some cases, surgery may be necessary. 

What are the complications of long QT syndrome?

LQTS can lead to torsades de pointes and ventricular fibrillation. These dangerous arrhythmias can lead to cardiac arrest and sudden cardiac death. 

How do you prevent long QT syndrome?

It is not possible to prevent the congenital form of LQTS. However, you can reduce symptoms and cardiac events by following your treatment plan. This includes avoiding events that trigger fainting and other symptoms. You will also need to avoid drugs that can aggravate the problem.

If you have a family history of LQTS, talk with your doctor about screening tests.

You may be able to prevent the acquired form of LQTS by avoiding drugs that cause it. Treating medical conditions that can cause it is another way to reduce your risk.

For people with LQTS, it is important to work with your pharmacist. Using the same pharmacy for all of your prescription needs is key. This allows your pharmacist to monitor all of your drugs and find potential problems.

Can you live a long life with long QT syndrome?

LQTS is rare but can be deadly. It is a leading cause of sudden death in healthy young people. It may also play a role in some cases of sudden infant death syndrome.

For most people, it is a lifelong condition and will require lifelong treatment. However, the risk of episodes and complications tends to decrease with age. This seems to be especially true for males over age 40. 

Summary

LQTS is a rare heart conduction disorder. It affects the electrical activity of the heart during ventricular contraction and relaxation. This can lead to life threatening heart arrhythmias.

One form of the disorder is genetic. Having a family member with the problem increases the risk of developing it. Testing can find gene mutations that cause this type of LQTS.

The other form is acquired, usually by having an electrolyte disorder or taking medicines that trigger it. Treatment involves lifestyle changes and medications and devices that control the heartbeat. 

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Medical Reviewer: Dr. Payal Kohli, M.D., FACC
Last Review Date: 2022 May 12
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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