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Long QT Syndrome and Torsades de Pointes Ventricular Tachycardia

By L. Brent Mitchell, MD, Professor of Medicine, Department of Cardiac Services, Libin Cardiovascular Institute of Alberta, University of Calgary

Torsades de pointes ventricular tachycardia is a specific type of ventricular tachycardia that occurs in people who have a particular disorder of the heart's electrical activity called long QT syndrome.

Some people are born with long QT syndrome. In other people, the disorder is caused by low serum levels of potassium, a very slow heart rhythm, or a drug. Often, antiarrhythmic drugs cause long QT syndrome, but certain antidepressants and certain antiviral and antifungal drugs can also cause it.

People with long QT syndrome may develop torsades de pointes ventricular tachycardia, and sometimes ventricular fibrillation. Sometimes, exercise brings on symptoms (see Sudden Cardiac Death in Athletes).

Did You Know...

  • The term "long QT" refers to an abnormal pattern of electrical activity that is seen on an electrocardiogram (ECG).


People with long QT syndrome may have palpitations (awareness of heartbeats) if ventricular tachycardia develops. They may also feel very light-headed or faint. Ventricular fibrillation causes cardiac arrest and sudden collapse.


  • Electrocardiography

Electrocardiography (ECG) is used to detect long QT syndrome.

Because some forms of long QT syndrome are inherited, people who have a family history of the disorder or have relatives who have died unexpectedly because of a heart problem may be tested for long QT syndrome.


  • Converting heartbeat to normal rhythm by applying an electric shock (defibrillation)

  • Preventing further episodes

Defibrillation is needed if ventricular fibrillation develops. Sometimes doctors also give magnesium sulfate.

If a drug is the cause, it is stopped.

People may need to limit their physical activity to prevent a recurrence. They may also need to take beta-blockers (see Table: Some Drugs Used to Treat Arrhythmias) or have an artificial pacemaker or cardioverter-defibrillator implanted.

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