Long QT syndrome (LQTS) is a heart rhythm condition that can potentially cause fast, chaotic heartbeats. These rapid heartbeats might trigger you to suddenly faint. Some people with the condition have seizures. In some severe cases, LQTS can cause sudden death.

Some people are born with a genetic mutation that causes long QT syndrome (congenital long QT syndrome). Long QT syndrome may be caused by certain medications, mineral imbalances or medical conditions (acquired long QT syndrome).

Long QT syndrome is treatable. You might need to avoid or take certain medications to prevent dangerous heartbeat episodes. Sometimes, treatment for long QT syndrome involves surgery or an implantable device.


Shedding light on dangerous faints

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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

Fainting is the most common sign of long QT syndrome.

Fainting (syncope) occurs when the heart temporarily beats in an unorganized way. You might faint when you're excited, angry or scared or during exercise. Things that startle you — for example, a telephone or an alarm clock — can cause you to lose consciousness. A fainting spell from long QT syndrome can occur with little to no warning. Some people have a warning sign first, such as lightheadedness, heart palpitations, weakness or blurred vision.

Seizures also may occur in some people with LQTS.

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 set your heartbeat back to normal, sudden death will occur.

Most people with symptoms of long QT syndrome have their first episode by age 40. However, congenital long QT syndrome signs and symptoms can occur in babies during the first weeks to months after birth, or in childhood or later. Some people with congenital long QT syndrome never have signs or symptoms.

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

When to see a doctor

Call your doctor if you suddenly faint during physical activity or emotional excitement or after taking any new medication. If you have a first-degree relative (parent, sibling or child) with long QT syndrome, it's important to let your doctor know. Long QT syndrome can run in families.


Long QT syndrome is a heart rhythm disorder caused by abnormalities in the heart's electrical recharging system. The heart's structure is normal.

Normally, the heart sends blood out to the body during each heartbeat. The heart's chambers contract and relax to pump the blood. This coordinated action is controlled by your heart's electrical system. Electrical signals (impulses) travel from the top to the bottom of your heart and trigger it to contract and beat. After each heartbeat, the system recharges itself to prepare for the next heartbeat.

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

Long QT syndrome is often grouped into two main categories, depending on the cause.

  • If you are born with the condition, it's called congenital long QT syndrome. Some forms of long QT syndrome result from a genetic mutation that is passed down through families (inherited).
  • If an underlying medical condition or medication causes it, it's called acquired long QT syndrome. This type of long QT syndrome is usually reversible when the underlying cause is identified.

Causes of congenital long QT syndrome

More than 17 genes have been linked to long QT syndrome so far, and researchers have identified hundreds of mutations within these genes.

Doctors have described two forms of congenital long QT syndrome:

  • Romano-Ward syndrome (autosomal dominant form). This more common form occurs in people who inherit only a single gene variant from one parent.
  • Jervell and Lange-Nielsen syndrome (autosomal recessive form). This rare form usually occurs earlier and is more severe. In this syndrome, children receive the faulty gene variants from both parents. The children are born with long QT syndrome and deafness.

Causes of acquired long QT syndrome

More than 100 medications — many of them common — can lengthen the QT interval in otherwise healthy people and cause acquired long QT syndrome.

Medications that can cause acquired long QT syndrome include:

  • Certain common antibiotics, such as erythromycin (Eryc, Erythrocin, others), azithromycin (Zithromax, Zmax) and others
  • Certain antifungal medications taken by mouth used to treat yeast infections
  • Diuretics that cause an electrolyte imbalance (low potassium, most commonly)
  • Heart rhythm drugs (especially anti-arrhythmic medications that lengthen the QT interval)
  • Certain antidepressant and antipsychotic medications
  • Some anti-nausea medications

If your condition is caused by a medication, it may be called drug-induced long QT syndrome. Always tell your doctor about all the medications you take, including those you buy without a prescription.

Other causes of acquired long QT syndrome include:

  • Low potassium level (hypokalemia)
  • Low calcium level (hypocalcemia)
  • Low magnesium level (hypomagnesemia)
  • COVID-19 infection

Risk factors

The following things may increase your risk of developing congenital or acquired long QT syndrome or its symptoms:

  • A history of cardiac arrest
  • Having a first-degree relative (parent, sibling) with long QT syndrome
  • Using medications known to cause prolonged QT intervals
  • Being female and on heart medication
  • Excessive vomiting or diarrhea
  • Eating disorders, such as anorexia nervosa, which cause electrolyte imbalances

Sexual intercourse doesn't appear to be high risk for patients with long QT syndrome. Pregnancy and delivery aren't associated with an increased risk of symptoms in women diagnosed with long QT syndrome. However, if you have the condition and are pregnant, your doctor will want to carefully monitor you during and after pregnancy.


Proper medical treatment and lifestyle changes can help prevent complications related to long QT syndrome.

Complications of long QT syndrome include:

  • Torsades de pointes ('twisting of the points'). This is a life-threatening form of ventricular arrhythmia. Your heart's two lower chambers (ventricles) beat fast and chaotically, making the waves on an ECG monitor look twisted. The heart pumps out less blood. The lack of blood to the brain causes you to faint suddenly and, often, without warning.

    If the episode lasts for a long time, fainting can be 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 stops 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.
  • Sudden death. It's now known that long QT syndrome might explain some cases of sudden death in young people who otherwise appear healthy.
  • Unexplained fainting, drownings, seizures or other accident. Long QT syndrome might be responsible for some otherwise unexplained deaths in children and young adults.


Congenital long QT syndrome is caused by a genetic mutation. There is no known prevention. However, with proper treatment, you can prevent the dangerous heartbeats that can lead to long QT syndrome complications.

You may be able to prevent the health conditions that lead to some types of acquired long QT syndrome with regular health checkups and good communication with your doctor. It is especially important to avoid medications that can affect your heart rhythm and cause prolongation of the QT interval.

Long QT syndrome care at Mayo Clinic

June 16, 2020
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