Many people with long QT syndrome don't have any signs or symptoms. They may be aware of their condition only from results of an electrocardiogram (ECG) performed for an unrelated reason, because they 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. In people with long QT syndrome, fainting spells (syncope) are caused by the heart temporarily beating in an erratic way. These fainting spells may happen when you're excited, angry, scared or during exercise. Fainting in people with long QT syndrome can occur without warning, such as losing consciousness after being startled by a ringing telephone.
Signs and symptoms that you're about to faint include lightheadedness, heart palpitations, irregular heartbeat, weakness and blurred vision. However, in long QT syndrome, such warning signs before fainting are unusual.
- Seizures. If the heart continues to beat erratically, the brain becomes increasingly deprived of oxygen. This can then cause generalized seizures.
- Sudden death. Normally, 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 may start during the first months of life, or as late as middle age. Most people who experience signs or symptoms from long QT syndrome have their first episode by the time they reach age 40.
Rarely, signs and symptoms of long QT syndrome may occur during sleep or arousal from sleep.
When to see a doctor
You should see 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, see 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.