Long QT Syndrome

Long QT syndrome (LQTS) is a disorder of the heart's electrical activity. It may cause you to develop a sudden, uncontrollable, and dangerous heart rhythm called an arrhythmia in response to exercise or stress.

Arrhythmias also can develop for no known reason in people who have LQTS. Not everyone who has LQTS develops dangerous heart rhythms; however, if one does occur, it may be fatal.

There are variations of LQTS. Emotional stress or exercise (especially swimming) that makes the heart beat fast tends to trigger abnormal heart rhythms if you have LQTS 1. In LQTS 2, abnormal rhythms may be triggered by surprise or other extreme emotions. In LQTS 3, a slow heart rate during sleep may trigger an abnormal heart rhythm.

Acquired, or noninherited, LQTS may be induced by certain medicines or other medical conditions.

The term "long QT" refers to an abnormal pattern seen on an EKG (electrocardiogram), which is a test that detects and records the heart's electrical activity. The QT interval, recorded on the EKG, corresponds to the time during which the lower chambers of your heart, ventricles, are triggered to contract and then build the potential to contract again.

The timing of the heartbeat's electrical activity is complex, and the body carefully controls it. Normally the QT interval of the heartbeat lasts about a third of each heartbeat cycle on the EKG.

However, in people who have LQTS, the QT interval usually lasts longer than normal. This can upset the careful timing of the heartbeat and trigger a dangerous, abnormal rhythm.


On the surface of each muscle cell in the heart are tiny pores called ion channels. Ion channels open and close to let electrically charged sodium, calcium, and potassium ions flow into and out of the cell, which generates the heart's electrical activity.

This activity causes each heart cell to contract. Normally, the electrical activity spreads from one heart cell to the next in an orderly and coordinated way. This allows the heart to pump blood efficently.

During each normal heartbeat, the muscle cells in the upper chambers of the heart, the atria, contract. The contraction pumps blood from the atria to the ventricles. Then the muscle cells in the ventricles contract, pumping blood from the ventricles to the lungs and the rest of the body.

This coordinated contraction of the atria and ventricles represents one normal heartbeat.

In people who have LQTS, there are problems with the ion channels in the heart cells that may disrupt the timing of the electrical activity in the ventricles. The ion channels may not work properly, or there may be too few of them. In this situation, the heart may suddenly develop a fast and abnormal heart rhythm that can be life threatening.

Many cases of LQTS are inherited, which means you're born with the condition and have it your whole life. There are seven known types of inherited LQTS, the most common being LQTS 1, LQTS 2, and LQTS 3.


For many people who have LQTS, lifestyle changes and medical treatments can help prevent dangerous complications and lengthen life expectancy. However, more than half of the people who have an untreated, inherited form of LQTS die within 10 years.

Some of these lifestyle changes and treatments include:

  • Avoiding strenuous physical activity or startling noises
  • Adding more potassium to your diet
  • Taking heart medicines called beta blockers, which are very effective at preventing sudden cardiac arrest
  • Having an implanted medical device, such as a pacemaker or implantable cardioverter defibrillator, that helps to control abnormal heart rhythms

Discuss with your doctor which lifestyle changes and treatments are appropriate for you and the type of LQTS you have.

Signs and Symptoms of Long QT Syndrome

Major Signs and Symptoms

If you have LQTS, you are prone to developing a sudden and dangerous arrhythmia. Signs and symptoms of LQTS-related arrhythmias often first appear during childhood and include:

  • Unexplained fainting - this happens because your heart isn't pumping enough blood to your brain. Fainting may occur when you're under physical or emotional stress. Some people will have fluttering feelings in their chests before they faint.
  • Unexplained seizures - those around you may mistake your fainting from LQTS as a seizure due to epilepsy. In children, fainting may be seen as a hysterical reaction to a stressful situation.
  • Unexplained drowning or near drowning - this may be due to fainting while swimming.
  • Unexplained sudden cardiac arrest (SCA) or death - this means that your heart suddenly stops beating for no obvious reason. People who have SCA will die within minutes unless they receive treatment. Most people who have SCA die. In about 1 out of 10 patients, SCA or sudden death is the first sign of LQTS.

Other Signs and Symptoms

Often, people who have LQTS 3 will develop an abnormal heartbeat during sleep. This may cause them to gasp loudly while sleeping.

Long QT Syndrome Without Symptoms

People who have LQTS may not have any signs or symptoms (silent LQTS). Doctors often advise family members of people who have the condition to be tested for it, even if they are asymptomatic.

Medical and genetic tests may reveal whether they have LQTS and what type of the condition they have.


Cardiologists, doctors who specialize in treating heart diseases and conditions, diagnose and treat LQTS. To diagnose LQTS, doctors consider:

  • EKG (electrocardiogram) results
  • Medical history and physical exam
  • Genetic test results


An EKG is a simple test that detects and records the heart's electrical activity. This test may reveal a long QT interval and other signs that make it more likely that you have LQTS. Often, doctors first discover a long QT interval when an EKG is done for another suspected heart problem.

Not all people who have LQTS will always have a long QT interval on an EKG. The QT interval may change from time to time; it may be long sometimes and normal at other times. Because of this, your doctor may want you to have several EKG tests over a period of days or weeks. Or, your doctor may have you wear a device called a Holter monitor.

A Holter monitor records the electrical signals of your heart for a full 24- or 48-hour period. You wear small patches called electrodes on your chest that are connected by wires to a small, portable recorder. The recorder can be clipped to a belt, kept in a pocket, or hung around your neck.

While you wear the monitor, you do your usual daily activities and note any symptoms you have and the time they occurred. You then return both the recorder and the symptom log  to your doctor to read the results, so your doctor can see how your heart was beating at the time you had symptoms.

The purpose of a Holter monitor is to detect heart problems that may occur for only a few minutes out of the day, and therefore would not likely be caught on a regular EKG.

Some people will only have a long QT interval on an EKG recording while they exercise. For this reason, your doctor may recommend that you have a stress test.

For this test, an EKG is done while you exercise. If you're unable to exercise, medicine may be injected into your bloodstream to make your heart work hard and beat fast, as if you were exercising.

Medical History and Physical Exam

Your doctor will ask whether you have had any symptoms of an abnormal heartbeat. Symptoms may include:

  • Unexplained fainting
  • A fluttering feeling in your chest due to your heart beating too fast
  • Loud gasping during sleep

Your doctor may ask what over-the-counter, prescription, or recreational drugs you take. He or she also may want to know whether anyone in your family has been diagnosed with or shows signs of LQTS.

Your doctor will examine you and look for signs of conditions that may lower blood levels of potassium or sodium. These conditions include the eating disorders such as anorexia nervosa and bulimia, excess vomiting or diarrhea, and certain thyroid disorders.

Genetic Tests

Genetic blood tests can detect some forms of inherited LQTS. If your doctor suspects that you have LQTS or a family member has it, he or she may recommend genetic testing.

However, genetic tests can't detect about one-third of LQTS cases. So, even if you have LQTS, the tests may not show it.

Also, as many as one-third of the people who test positive for LQTS do not have any signs or symptoms of the disorder. These people may have silent LQTS; less than 10 percent of these people will faint or suddenly die from an abnormal heartbeat.

Even if you have silent LQTS, you may be at higher risk than most people for developing an abnormal heartbeat while taking medicines that affect potassium ion channels or blood levels of potassium.

Types of Inherited LQTS

If you have inherited LQTS, it may be helpful to know which of the seven inherited types of the syndrome you have. This will help you and your doctor plan your treatment and decide which lifestyle changes you should make.

To find out what type of LQTS you have, your doctor will consider:

  • Genetic test results
  • The types of situations that trigger an abnormal heartbeat
  • How well you respond to medicine


The goal of treating long QT syndrome (LQTS) is to prevent life-threatening, abnormal heartbeats and fainting spells. Treatment is not a cure for this condition and may not restore a normal QT interval on an EKG, but treatment does greatly improve chance of survival.

Specific Types of Treatment

Your doctor will recommend the best treatment for you based on:

  • Whether you've had symptoms, such as fainting or sudden cardiac arrest (SCA)
  • What type of LQTS you have
  • How likely it is that you will faint or that your heart will suddenly stop beating
  • What treatment you feel most comfortable proceeding with

People who have LQTS but no symptoms may be advised to:

  • Make lifestyle changes that reduce the risk of fainting or SCA. These may include avoiding competitive sports and strenuous exercise, such as swimming, which can cause abnormal heartbeats.
  • Avoid medicines that may trigger symptoms. This may include some medicines used to treat allergies, infections, high blood pressure, high blood cholesterol, and depression.
  • Take medicines, such as beta-blockers, which reduce the risk of symptoms by slowing your heart rate.

The type of LQTS you have will determine which medicines you take to avoid abnormal heart rhythms. For example, doctors usually only will prescribe sodium channel blocker medicines for people who have LQTS 3.

If your doctor thinks you're at higher risk for LQTS complications, he or she may suggest other, more aggressive, treatments in addition to medicines and lifestyle changes. Such aggressive treatments include:

  • A surgically implanted device, such as a pacemaker or implantable cardioverter defibrillator (ICD) to help regulate your heartbeat.
  • Surgery on the vagus nerve that regulate your heartbeat.

People at higher risk are those who have fainted or have developed dangerous heart rhythms from their LQTS in the past.

Lifestyle Changes

If you have LQTS, you should try to avoid the specific triggers you have for an abnormal heartbeat. Many people who have LQTS also benefit from adding more potassium to their diets.

Check with your doctor about eating more potassium-rich foods, such as bananas, or taking potassium supplements daily.

People who have LQTS should also avoid medicines that lengthen the QT interval or lower potassium blood levels. (For more information, go to "What Causes Long QT Syndrome?")


Beta blockers are medicines that prevent the heart from beating faster in response to physical or emotional stress. Most people who have LQTS are treated with beta blockers.

Doctors may suggest that people who have LQTS 3 take sodium channel blockers, such as mexiletine. These medicines make sodium ion channels less active.

Pacemaker or Implantable Cardioverter Defibrillator

These surgically implanted devices monitor the heart rhythm. They deliver electrical currents to the heart when they detect an abnormal heart rhythm. Surgeons implant pacemakers and ICDs in the chest or belly with a minor procedure.


People who are at high risk of death from LQTS are sometimes treated with surgery. During this surgery, the nerves that prompt the heart to beat faster in response to physical or emotional stress are cut.

This helps keep the heart beating at a steady pace and decreases the chances of developing dangerous heart rhythms in response to stress or exercise.