What is short Q-T syndrome (SQTS)?

Short Q-T syndrome is a rare genetic type of abnormal heart rhythm that was discovered in 1999.

The electrical activity of the heart is produced by the flow of ions (electrically charged particles of sodium, calcium, potassium, and chloride) in and out of the cells of the heart. Tiny ion channels control this flow. The Q-T interval is the section on theelectrocardiogram (ECG) that represents the time it takes for the electrical system to fire an impulse through the ventricles (lower chambers of the heart) and then recharge. It is translated to the time it takes for the heart muscle to contract and then recover.

If you have SQTS, your heart beats at a normal rate, but the time it takes to recover (the Q-T interval) is much shorter. Another difference in patients with SQTS is that the Q-T interval does not change as the speed of the heartbeat changes. In healthy people, the Q-T interval gets longer when the heart beats slower and shorter when the heart beats faster.

Normal QT

  • Resting Rate: 60 bpm
  • QT Interval: 350-440 milliseconds4

Short QT

  • Resting Rate: 60 bpm
  • QT Interval: 210 to 340 milliseconds

What are the symptoms of SQTS?

The majority of patients with SQTS have symptoms. The most common symptoms are:

  • Heart pounding (palpitations)
  • Fainting (syncope)
  • Sudden cardiac death (may be the first symptom for some patients)
  • Atrial fibrillation

If SQTS causes atrial fibrillation, other symptoms may include shortness of breath, dizziness, fatigue and chest discomfort.

Some people with SQTS never have symptoms or problems related to the condition. But, it is important for anyone who knows they have SQTS to see a doctor for regular care to prevent sudden cardiac death or cardiac arrest.

What causes SQTS?

Short Q-T syndrome is a congenital defect, which means it is present at birth. The condition is inherited from at least one parent. The defect changes the way the heart’s ion channels function (called a channelopathy).So far, scientists have found several different defects that can occur in five different genes related to the potassium channels. However, in most cases, the gene is not identified. Research is being done to identify other genes.

What problems does SQTS cause?

When there is abnormal electrical activity in the heart, the heart muscle discharges and recharges faster than normal. This can cause three types of abnormal heart rhythms ─ atrial fibrillation, ventricular tachycardia and ventricular fibrillation. If you have SQTS, you can have one or more of these.

  • Atrial fibrillation is an abnormal heart rhythm that starts in the atria (the heart’s upper chambers). Some people with SQTS have occasional atrial fibrillation, while the problem can be almost constant for others.
  • Ventricular tachycardia is a very fast regular rhythm in the ventricles (the heart’s lower chambers).
  • Ventricular fibrillation is a very fast abnormal rate causing the ventricles to flutter or quiver. It causes sudden cardiac death.

Last reviewed by a Cleveland Clinic medical professional on 07/19/2019.

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