Heart and Blood Conditions

Long QT Syndrome Symptoms and Diagnosis

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    • Seattle Children's Main Campus: 206-987-2515
    • Bellevue Clinic and Surgery Center: 425-454-4644
    • Everett: 425-304-6080
    • South Clinic in Federal Way: 253-838-5878
    • Olympia: 360-459-5009
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    • Seattle Children's doctors provide many cardiac services at regional sites throughout the Pacific Northwest. See our complete list of Heart Center locations.

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    • If you are a provider, fax a New Appointment Request Form (NARF) (PDF) (DOC) to 206-985-3121 or 866-985-3121 (toll-free).
    • No pre-referral work-up is required for most conditions. If you have already done testing such as an EKG, Holter monitor or echocardiogram, please fax this information as well as relevant clinic notes and the NARF to 206-985-3121 or 866-985-3121 (toll-free).
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    • View our complete Heart Center Referral Information (PDF).

Symptoms of Long QT Syndrome

Children with long QT syndrome (LQTS) usually do not have symptoms unless they develop an arrhythmia. If their heart begins beating too fast, they might faint because their brain isn’t getting enough blood. Symptoms that occur with fainting may include dizziness, heart palpitations, heart racing and blurred vision.

Sometimes a fainting spell is mistaken for a seizure or it seems like a response to stress. In other cases, a child drowns because they fainted while swimming.

Your child should be seen by their healthcare provider if they faint, have a seizure or nearly drown and there’s no clear reason. They should also be checked if you already know they have LQTS or if there are other family members with the condition.

The heart of someone with LQTS can suddenly stop beating, a condition called sudden cardiac arrest. This may be the first sign of LQTS. Sudden cardiac arrest usually causes death. However, some children who receive treatment quickly, within minutes, can survive.

Long QT Syndrome Diagnosis

To diagnose this condition, your doctor will examine your child and use a stethoscope to listen to their heart. The doctor will ask for details about any symptoms your child has, their health history and your family health history.

Your child will also have an electrocardiogram (ECG) test to tell doctors information about how your child’s heart works.

Using an ECG, a healthcare provider can examine the electrical signal in your child’s heart. The signal produces a pattern. Providers name different parts of the patterns with the letters P, Q, R, S and T. The time from when the ventricles start to squeeze until they are relaxed and ready to squeeze again is the “QT interval.”

A provider can measure this time and know if it takes longer than normal. If it takes longer, it’s called a “prolonged QT interval.” A child with a prolonged QT interval may have LQTS.

An ECG will not always detect LQTS because some children do not have a prolonged QT interval all of the time. To get enough information about the electrical signal in your child’s heart, your child may need to wear a portable ECG device called a Holter monitor. This device can record their heart’s activity for 24 hours.

You child may also need an exercise test. This means we monitor their heart rate and rhythm while they exercise.

The doctor may suggest doing genetic testing to see if genes play a role in your child’s condition. If they do, then others in the family may need to be tested to see if they might be affected.