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Long QT Syndrome and Torsades de Pointes Ventricular Tachycardia

By

L. Brent Mitchell

, MD, Libin Cardiovascular Institute of Alberta, University of Calgary

Last full review/revision Feb 2021| Content last modified Feb 2021
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Topic Resources

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.

The QT interval refers to the time between two events on the electrocardiogram—from the beginning of the Q wave to the end of the T wave.

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, drugs used to treat abnormal heart rhythms 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).

Symptoms

People with long QT syndrome may have palpitations (awareness of heartbeats) if ventricular tachycardia develops. Torsades de pointes runs of ventricular tachycardia usually stop on their own but frequently recur. People may also feel very light-headed or faint. Ventricular fibrillation causes cardiac arrest and sudden collapse.

Diagnosis

  • 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.

ECG: Reading the Waves

An electrocardiogram (ECG) represents the electrical current moving through the heart during a heartbeat. The current's movement is divided into parts, and each part is given an alphabetic designation in the ECG.

Each heartbeat begins with an impulse from the heart's pacemaker (sinus or sinoatrial node). This impulse activates the upper chambers of the heart (atria). The P wave represents activation of the atria.

Next, the electrical current flows down to the lower chambers of the heart (ventricles). The QRS complex represents activation of the ventricles.

The ventricles must then undergo an electrical change to get ready for the next heart beat. This electrical activity is called the recovery wave, which is represented by the T wave.

Many kinds of abnormalities can often be seen on an ECG. They include a previous heart attack (myocardial infarction), an abnormal heart rhythm (arrhythmia), an inadequate supply of blood and oxygen to the heart (ischemia), and excessive thickening (hypertrophy) of the heart's muscular walls.

Certain abnormalities seen on an ECG can also suggest bulges (aneurysms) that develop in weaker areas of the heart's walls. Aneurysms may result from a heart attack. If the rhythm is abnormal (too fast, too slow, or irregular), the ECG may also indicate where in the heart the abnormal rhythm starts. Such information helps doctors begin to determine the cause.

ECG: Reading the Waves

Treatment

  • 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.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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