Long QT syndrome

Long QT syndrome is an inherited heart rhythm problem where the heart muscle takes longer than normal to recharge between beats. In some people, this can cause fainting or fits (seizures).

Long QT syndrome is uncommon, affecting about 1 in every 2,000 people.

Symptoms

Some people with long QT syndrome don’t have any symptoms. They may only become aware of their condition after having an electrocardiogram (ECG) for another reason.Those who do have symptoms usually experience:

  • blackouts or fainting, because the heart has stopped pumping blood properly and the brain is temporarily starved of oxygen – the heart’s rhythm returns to normal within a minute or two and the person regains consciousness
  • seizures, which sometimes happen instead of a blackout when the brain is starved of oxygen
  • heart palpitations, when the heart is beating in a fast or unpredictable way

These symptoms can start unexpectedly and may be triggered by:

  • stress
  • a sudden noise – such as an alarm
  • strenuous exercise – particularly swimming
  • a slow heart rate during sleep

Risk of death

The heart usually returns to its normal rhythm after it’s been beating abnormally, but if it continues to beat abnormally it may result in ventricular fibrillation and ultimately sudden cardiac arrest.

Long QT syndrome is a leading cause of sudden cardiac death in young, otherwise healthy, people. It can also be an underlying cause of sudden infant death syndrome (SIDS).

Causes

Long QT syndrome is usually caused by a faulty gene inherited from a parent.

The abnormal gene affects the proteins that make up the ion channels regulating electricity in the heart. The ion channels may not work well, or there may not be enough of them, which disrupts the heart’s electrical activity.

Certain medicines can also trigger long QT syndrome, including some types of:

But drug-induced long QT syndrome tends to only affect people who already have a tendency to develop the condition.

See the NHS website for detailed information.