Testing & Diagnosis for Long QT Syndrome LQTS in Children

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Contact the Inherited Cardiac Arrhythmia Program

Clinical diagnosis of Long QT Syndrome is difficult, as many do not experience symptoms. If your doctor suspects that your child has Long QT Syndrome, (due to episodes of fainting or arrhythmias), he/she may suggest medical testing in addition to a complete medical history and physical examination. Our approach at Boston Children’s is to evaluate the family as well as the patient history since the individual patient may not be symptomatic. We have a structured approach that evaluates the type of Long QT Syndrome and the clinical risk stratification through a series of diagnostic tests that may also include genetic analysis.

Electrocardiogram (EKG or ECG)

An electrocardiogram is one of the simplest and fastest procedures used to evaluate the heart. Before the test, electrodes (small, plastic patches) are placed at certain locations on your child's chest, arms and legs. After the electrodes are connected to the EKG/ECG machine by lead wires, the electrical activity of your child's heart is measured and printed out for the physician to evaluate.


Echocardiography is a procedure that evaluates the structure and function of the heart by using sound waves to produce a moving picture of the heart and heart valves. The picture is much more detailed than a plain X-ray image and involves no radiation exposure. Types of echocardiography include cardiac ultrasound, cardiac Doppler, transesophageal echocardiography (TEE).

Exercise electrocardiogram

Exercise EKG testing (also called a stress EKG or stress ECG) measures cardiac rhythm and function by having a patient exercise on a treadmill or bicycle.

Holter monitoring

A Holter monitor is a tiny, portable EKG machine that is worn for a 24-hour period or longer to look for signs of irregular, fast or slow heart rhythms during normal activities. Your child will have tiny patches on their chest that attach with lead wires to the small monitor.

Event Monitoring

An event monitor is similar to a Holter monitor, and is used to test for symptoms that occur less frequently. There are three kinds of event monitors:

Leadless: These monitors are designed to capture post-event activity. This small flat recorder that is placed against your child’s chest over her heart at the first sign of symptoms. You will need to manually record the ECG sample by pressing a button once the recorder is in place.

  • Looping Recorder worn with electrodes/leads: This recorder constantly records and erases (loops over) your child’s ECG. When your child feels symptoms you will need to press the device's Record button to capture the ECG at that moment in time. The recorder also saves a short sample of the time before the symptom, enabling your clinician to see what was happening in your child's heart, before, during and after the symptoms.
  • Automatically triggered recorder: Works the same as a looping recorder but can detect sudden changes in heart rate and automatically capture that information.
  • Magnetic Resonance Imaging (MRI) - MRI is a procedure that uses a combination of large magnets, radiofrequencies and a computer to produce detailed images of organs and structures with the body.
  • Genetic Analysis: Genetic testing has become increasingly effective in identifying family members at risk of this rare condition. Because LQTS can be inherited, your child's cardiologist may suggest that other family members also undergo genetic testing.
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