To diagnose long QT syndrome, your doctor will perform a physical exam and ask questions about your or your child's symptoms and medical and family history. Your doctor will use a stethoscope to listen to your heart.
An electrocardiogram is the most common test used to diagnose long QT syndrome.
Electrocardiogram (ECG or EKG)
An electrocardiogram is a quick and painless test that records the electrical signals in your heart. You might have an ECG while at rest or while exercising on a treadmill or stationary bicycle. If you cannot safely exercise, you may be given a medication such as epinephrine (Adrenalin) that stimulates your heart in a way similar to exercise.
During an ECG, sticky patches (electrodes) are placed on your chest to record your heart's electrical signals, which cause your heart to beat. The signals are shown as waves on an attached computer monitor or printer.
An ECG can tell if you are having a prolonged QT interval. The test labels the heart's electrical signals as five waves using the letters P, Q, R, S and T. The waves labeled Q through T show the electrical activity in your heart's lower chambers (ventricles).
The space between the start of the Q wave and the end of the T wave is the QT interval. That's the time it takes for your heart to contract and refill with blood before it beats again.
What's normal for you depends on your age, your sex and your individual heart rate. Your doctor will consider this information. If the interval takes longer than normal to occur, it's called a prolonged QT interval.
Remote ECG monitoring
If your long QT symptoms tend to come and go, they may not be captured during a standard ECG recording. In this case your doctor may recommend remote or continuous ECG monitoring. There are several different types.
- Holter monitor. A Holter monitor is a small, wearable device that records a continuous ECG, usually for 24 to 48 hours.
- Event monitor. This portable device is similar to a Holter monitor, but it records only at certain times for a few minutes at a time. You can wear it longer than a Holter monitor, typically 30 days. You generally push a button when you feel symptoms. Some devices automatically record when an abnormal rhythm is detected.
A genetic test for long QT syndrome is available and recommended by many doctors to confirm the diagnosis. Check with your insurer to see if it is covered.
It's important to understand that genetic tests for long QT syndrome can't detect all inherited cases of long QT syndrome. It's recommended that families speak to a genetic counselor before and after testing.
If you have a positive genetic test for long QT syndrome, your doctor may recommend that other family members also be tested to determine whether they inherited the same gene.