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Long QT syndrome

Medically reviewed by Drugs.com. Last updated on Jan 12, 2024.

Overview

Long QT syndrome (LQTS) is a heart signaling disorder that can cause fast, chaotic heartbeats (arrhythmias). A heart signaling disorder is also called a heart conduction disorder.

Some people are born with altered DNA that causes long QT syndrome (congenital long QT syndrome). Long QT syndrome may also occur later in life (acquired long QT syndrome) as the result of some medical conditions, certain drugs or mineral imbalances.

Long QT syndrome can cause sudden fainting and seizures. Young people with LQTS syndrome have an increased risk of sudden death.

Treatment for long QT syndrome includes lifestyle changes and medications to prevent dangerous heartbeats. Sometimes surgery is needed to implant a device to control the heart's rhythm.

Symptoms

Some people with long QT syndrome (LQTS) do not have any noticeable symptoms. The condition may be discovered when an electrocardiogram (ECG) or genetic testing is done for other reasons.

Fainting (syncope) is the most common symptom of long QT syndrome. A fainting spell from long QT syndrome can occur with little to no warning. Some people have fainting warning signs first, including:

Fainting 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.

Long QT syndrome may also cause seizures in some people. Symptoms of long QT syndrome sometimes occur during sleep.

Most people with symptoms of LQTS have their first episode by age 40. When the condition is present at birth (congenital long QT syndrome), symptoms may occur during the first weeks to months of life or later in childhood.

Generally, after a long QT episode, the heart returns to its typical rhythm. If the heart doesn't reset itself or if an external defibrillator isn't used in time to reset the heart rhythm, sudden death will occur.

When to see a doctor

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

Causes

Long QT syndrome is a heart rhythm disorder caused by changes in the heart's electrical recharging system. It doesn't affect the heart's structure.

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

In long QT syndrome, the heart's electrical system takes longer than usual to recharge between beats. This delay is called a prolonged QT interval. It may be seen on an electrocardiogram (ECG).

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

Causes of congenital long QT syndrome

More than a dozen genes have been linked to long QT syndrome so far. Researchers have identified hundreds of alterations within these genes.

There are two forms of congenital long QT syndrome:

Causes of acquired long QT syndrome

More than 100 medications — many of them common — can cause prolonged QT intervals in otherwise healthy people.

If a medication causes acquired long QT syndrome (LQTS), the condition may be called drug-induced long QT syndrome. Medications that can cause LQTS include:

Always tell your health care provider about all the medications you take, including those you buy without a prescription.

Health conditions that can lead to acquired long QT syndrome include:

Chambers and valves of the heart

A typical heart has two upper and two lower chambers. The upper chambers, the right and left atria, receive incoming blood. The lower chambers, the more muscular right and left ventricles, pump blood out of the heart. The heart valves, which keep blood flowing in the right direction, are gates at the chamber openings.

Risk factors

The following things may increase the risk of developing long QT syndrome:

If you have long QT syndrome and are considering pregnancy, tell your health care provider. Your health care provider will want to carefully monitor you during pregnancy to help prevent things that can trigger an LQTS episode.

Complications

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

Potential complications of long QT syndrome include:

Prevention

Regular health checkups and good communication with your health care provider may help prevent health conditions that lead to some types of acquired long QT syndrome. It's especially important to avoid medications that can affect the heart rhythm and cause a prolonged QT interval.

There is no known prevention for congenital long QT syndrome. Families with inherited long QT syndrome might consider genetic screening. With proper treatment, you can manage and prevent the dangerous heartbeats that can lead to long QT syndrome complications.

Diagnosis

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

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)

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 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.

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.

Genetic testing

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.

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.

Treatment

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

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:

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:

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.

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.

Preparing for an 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:

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

Questions to ask the health care provider at your first appointment include:

Questions to ask if you're referred to a cardiologist or electrophysiologist include:

Questions to ask if your health care provider recommends surgery include:

Additional questions include:

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 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.

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