Symptoms

Many people who have long QT syndrome don't have any signs or symptoms. You might be aware of your condition only because of:

• Results of an electrocardiogram (ECG) done for an unrelated reason
• A family history of long QT syndrome
• Genetic testing results

Fainting is the most common sign of long QT syndrome.

Fainting (syncope) occurs when the heart temporarily beats in an unorganized way. You might faint when you're excited, angry or scared or during exercise. Things that startle you — for example, a telephone or an alarm clock — can cause you to lose consciousness. A fainting spell from long QT syndrome can occur with little to no warning. Some people have a warning sign first, such as lightheadedness, heart palpitations, weakness or blurred vision.

Seizures also may occur in some people with LQTS.

Generally, the heart returns to its normal rhythm. If this doesn't happen by itself, or if an external defibrillator isn't used in time to set your heartbeat back to normal, sudden death will occur.

Most people with symptoms of long QT syndrome have their first episode by age 40. However, congenital long QT syndrome signs and symptoms can occur in babies during the first weeks to months after birth, or in childhood or later. Some people with congenital long QT syndrome never have signs or symptoms.

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

When to see a doctor

Call your doctor if you suddenly faint during physical activity or emotional excitement or after taking any new medication. If you have a first-degree relative (parent, sibling or child) with long QT syndrome, it's important to let your doctor know. Long QT syndrome can run in families.