Many people who have long QT syndrome don't have any signs or symptoms. You might be aware of your condition only from results of an electrocardiogram (ECG) done for an unrelated reason, because you have a family history of long QT syndrome or because of genetic testing results.

For people who do experience signs and symptoms of long QT syndrome, the most common long QT symptoms include:

  • Fainting. This is the most common sign of long QT syndrome. Long QT syndrome-triggered fainting spells (syncope) are caused by the heart temporarily beating in an erratic way. These fainting spells might happen when you're excited, angry, scared or during exercise.

    Fainting can occur without warning, such as losing consciousness after being startled by a ringing telephone. Unlike normal fainting spells that are preceded by warning signs such as lightheadedness, heart palpitations, irregular heartbeat, weakness and blurred vision, long QT syndrome-triggered fainting spells can occur with little to no warning.

  • Seizures. If the heart continues to beat erratically, the brain becomes increasingly deprived of oxygen, which can cause seizures.
  • Sudden death. Generally, the heart returns to its normal rhythm. If this doesn't happen spontaneously and paramedics don't arrive in time to convert the rhythm back to normal with an external defibrillator, sudden death will occur.

Signs and symptoms of inherited long QT syndrome might start during the first weeks to months after birth, or as late as older age, or never at all. Most people who experience signs or symptoms from long QT syndrome have their first episode by age 40.

Signs and symptoms of long QT syndrome might occur during sleep or arousal from sleep.

When to see a doctor

Consult your doctor if you suddenly faint during physical exertion or emotional excitement or after use of a new medication.

Because long QT syndrome can occur in families, ask your doctor to be tested for long QT syndrome if a first-degree relative (parent, sibling or child) has been diagnosed with long QT syndrome.

Oct. 27, 2015