What is long QT syndrome?

Long QT syndrome is a rare heart rhythm condition that affects approximately one in 6,000 people in the United States. It can cause dangerous arrhythmias that can occur when the body is under mental or physical stress.

The QT interval represents the amount of time it takes for the heart to contract, recover and to contract again. If the QT interval takes longer than normal, it can cause a serious form of ventricular tachycardia that can be life-threatening.

Long QT syndrome can be treated with medications to prevent abnormal heart rhythms. In severe cases, you may need surgery or an implantable device.

Common related conditions
Tachycardia Arrhythmia (Fast Heartbeat) Bradycardia Arrhythmia (Slow Heartbeat) Atrial Flutter Atrial Fibrillation (AFib) Wolff-Parkinson-White Syndrome

Causes of long QT syndrome

Long QT syndrome occurs when the time it takes your heart to recharge between heartbeats becomes prolonged and causes arrhythmias. The QT interval becomes prolonged due to abnormalities in the heart’s electrical system — the heart’s electrical activity is produced by the flow of particles such as calcium, sodium, potassium and chloride into and out of the heart.

Long QT syndrome can be inherited or acquired.

Inherited long QT syndrome

Many people with long QT syndrome are born with the condition and live with it their entire lives. Faulty genes that cause the body to produce too few ion channels, ion channels that don’t work well or both can cause inherited long QT syndrome.

Research shows a link between sudden infant death syndrome (SIDS) and long QT syndrome. An estimated 5 to 10 percent of babies who pass away from SIDS had long QT syndrome caused by a genetic defect.

Acquired long QT syndrome

The most common cause of acquired long QT syndrome is the use of medications. There are more than 100 medications that can lead to long QT syndrome in healthy people. When this occurs, it is known as drug-induced long QT syndrome.

Medications that cause long QT syndrome include:

  • Antibiotics
  • Antidepressants and antipsychotic medications
  • Antihistamines
  • Diuretics
  • Antiarrhythmic medications
  • Anti-nausea medications

Other causes of acquired long QT syndrome include electrolyte abnormalities and medical conditions.

Risk factors for long QT syndrome

There are a variety of factors that can increase your risk of developing long QT syndrome. Factors include:

  • Age — people under the age of 25 who have a history of cardiac arrest, unexplained fainting or unexplained near drownings.
  • Gender — women are more likely to develop long QT syndrome than men.
  • Family history — people who have family members who have LQTS are more likely to develop long QT syndrome, all family members should be tested.
  • People with anorexia nervosa — patients with anorexia are more likely to have low potassium, magnesium or calcium levels and are at higher risk for developing long QT syndrome.

Symptoms of long QT syndrome

Although most people who have long QT syndrome do not experience symptoms, for those who do, symptoms include fainting, seizures or sudden cardiac arrest/death.

These symptoms are related to a ventricular tachycardia called torsade de pointes that causes the heart to beat very fast and in irregular rhythm. During this arrhythmia, the body does not receive the blood supply it needs to function and symptoms can occur.

Symptoms will cease when the heart rhythm returns to a normal pattern. In cases where the symptoms do not stop, sudden death will occur.

Unexplained fainting is the most common sign of long QT and can occur during exercise or when you are excited, angry or scared.

Diagnosis of long QT syndrome

Long QT syndrome can be diagnosed and treated by your cardiologist. If your doctor suspects you have long QT syndrome, he or she may order a diagnostic test such as:

  • Electrocardiogram (ECG) — one of the most effective tool used to diagnose long QT syndrome because it can measure the duration of time between each heartbeat.
  • Holter monitor — a portable ECG that is worn over the course of a day or more to monitor a patient’s heart activity over a normal day.
  • Event monitor — a portable ECG that records heart events as they happen (the patient pushes a button when they experience heart palpitations).

Treatment for long QT syndrome

The goal of treatment for long QT syndrome is to manage symptoms and avoid sudden cardiac death. Your doctor will discuss the various treatment options with you and develop a plan that is most appropriate for your case.

If you have acquired long QT syndrome as a result of taking certain medications, your doctor will likely switch your medication to another one that does not cause symptoms.

Medications for long QT syndrome

QT syndrome can be managed with medications such as:

  • Beta blockers — slow the heart rate to decrease the likelihood of long QT syndrome.
  • Mexiletine — reduce the QT interval when used in conjunction with a beta blocker.
  • Spironolactone and potassium — helps the body retain potassium and potassium supplements.

Surgical treatments for long QT syndrome

In more severe cases, your doctor may recommend implanting a surgical device such as:

  • Implantable cardioverter defibrillator (ICD) — can detect heart rhythm abnormalities and can slow the heart to restore normal heart rhythm.
  • Pacemaker — if you have an abnormally slow heart rate, a pacemaker may be an option to restore normal heart rate during a prolonged QT episode.
  • Left cardiac sympathetic denervation surgery — removal of nerves in the sympathetic nervous system to reduce the risk of sudden death.

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