Long QT Syndrome

Diagnosis

Mayo Clinic doctors trained in heart disease (cardiologists) and other doctors diagnose people who have long QT syndrome (LQTS).

To diagnose long QT syndrome, your doctor will review your medical and family history and conduct a physical examination. Your doctor may order several tests to diagnose your condition.

• Electrocardiogram (ECG). In an ECG, doctors place sensor patches (electrodes) on your skin to measure the electrical impulses given off by your heart. An ECG measures the timing and rhythm of each electrical phase in your heartbeat. Doctors often use an ECG to diagnose people who have long QT syndrome.
• Holter monitor. A Holter monitor is a portable ECG device that you wear for a day or more to record your heart's electrical activity during your daily routine.
• Stress test. In a stress test, your heart is monitored by an ECG or other tests as you exercise on a treadmill or stationary bicycle. If you have difficulty exercising, your doctor may give you a drug to help stimulate your heart in a similar way as during exercise.
• Genetic tests. Your doctor may order genetic tests to check for several gene mutations known to cause inherited LQTS. Genetic tests don't always identify inherited LQTS. You sometimes may have the condition even though the genetic test results were negative.

Read more about long QT syndrome diagnosis.