beth israel deaconess medical center a harvard medical school teaching hospital

To find a doctor, call 800-667-5356 or click below:

Find a Doctor

Request an Appointment

left banner
right banner
Smaller Larger


Diagnostic Tests

If your doctor suspects you have long QT syndrome, he or she will ask about symptoms you may be having and family history. He or she also may order one or more of the following tests to see if you have a lengthened QT interval:

Electrocardiogram (ECG)


Painless, Noninvasive Test Using Electrodes

This is a painless, noninvasive test in which patches with electrodes are attached to your skin to measure electrical impulses produced by your heart. These impulses are recorded as waves displayed on a monitor or printed out on graph paper.

Shows Heart Rate and Rhythm

It shows how fast your heart is beating and its rhythm (steady or irregular). It also records the timing of the electrical signals as they pass through each part of the heart.

Holter Monitor

Records Heartbeats for 24 or 48 Hours

This is a portable device that records all of your heartbeats over an extended period, usually either 24 or 48 hours.

  • You wear small patches with electrodes on your chest that are connected by wires to a small, portable recorder.
  • The recorder can be clipped to a belt, kept in a pocket, or hung around your neck.
  • During the time you're wearing a Holter monitor, you do your usual daily activities.
  • You can press a button if you are experiencing symptoms, so your doctor will know what your heart rhythm was at the time of the symptoms.

Event Monitor

Records Electrical Activity When You Push A Button

This machine is similar to the Holter monitor, except that not all of your heartbeats are recorded.

  • You wear the device continuously, but it only records electrical activity when you push a button -- and you only push the button when you feel symptoms.
  • These devices may be worn for as long as one to two months.

Additional Tests

Sometimes, the EKG, holter monitor or event monitor will not find a lengthened QT interval. If this is the case, other tests may be needed. These may include:

Medication Stress Test

EKG Taken While Taking A Stimulant

This is an EKG given while you are taking a medication such as adrenaline that stimulates your heart much like exercise would. In this test, your doctor can monitor how adrenaline affects how your heart recharges.

Electroencephalogram (EEG)

Records Brain Waves

This test looks for neurological causes of fainting, such as a seizure disorder. It measures waves of electrical activity produced by the brain. Electrodes attached to your head record electrical impulses from your brain and send them to the EEG machine, so brain waves can be recorded.

Genetic Tests

A genetic screening test is available for the most common genes associated with LQTS. These genes explain most but not all cases, so you may test negative but still have LQTS. If you test positive, then family members may also want to be tested.

Contact Information

Cardiovascular Medicine
Division of the CardioVascular Institute
Beth Israel Deaconess Medical Center
330 Brookline Avenue
Boston, MA 02215