Conditions + Treatments

Long QT Syndrome LQTS Symptoms & Causes

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Contact the Inherited Cardiac Arrhythmia Program

What is Long QT Syndrome?

Long QT Syndrome (LQTS) is an inherited condition that affects the heart’s electrical rhythm and can cause fast, erratic heartbeats. It is characterized by a prolonged QT interval on an EKG.


  • The first little upward notch of the EKG tracing is called the "P wave." The P wave indicates that the atria (the two upper chambers of the heart) are contracting to pump out blood.
  • The next short flat segment is called the "PR interval." This represents the delay in the propagation of the electrical signal from the atria to the ventricles.
  • The next part of the tracing is a short downward section connected to a tall upward section. This next part is called the "QRS complex." This part indicates that the ventricles (the two lower chambers of the heart) are contracting to pump out blood to the body (depolarization).
  • The next short upward segment is called the "ST segment." The ST segment indicates the amount of time from the end of the contraction of the ventricles to the beginning of the rest period before the ventricles begin to contract for the next beat.
  • The next upward curve is called the "T wave." The T wave indicates the resting period of the ventricles.

When your child's doctor studies your child's EKG, she looks at the size and length of each part of the EKG. Variations in size and length of the different parts of the tracing may be significant.

The tracing for each lead of a 12-lead EKG will look different, but will have the same basic components as described above. Each lead of the 12-lead EKG is "looking" at a specific part of the heart from different angles. Variations in a lead may indicate a problem with the part of the heart associated with that particular lead.

In most instances LQTS is caused by an inherited genetic mutation passed down from a family member. Someone who has a first-degree relative—a parent or sibling—with an inherited arrhythmia like LQTS has a 50 percent chance of having the condition themselves as well. LQTS causes approximately 3,000 to 4,000 sudden deaths children and young adults each year in the United States. It can affect children and young adults, with most patients experiencing their first episode before the age of 40.

Symptoms of Long QT Syndrome include:

  • Palpitations (fast heart beat)
  • Syncope (fainting) during periods of strenuous exercise or emotional distress
  • Seizures
  • Cardiac arrest

What are the different types of Long QT Syndrome?

Long QT Syndrome can occur with symptoms or be asymptomatic (which is when family screening is particularly important. Long QT Syndrome is typically diagnosed as one of the following three types:

  • LQT1: Patients are more likely to have symptoms with exercise/emotional stress
  • LQT2: Patients are more likely to have symptoms with emotional stress
  • LQT3: Patients are more likely to have symptoms during periods of rest or sleep
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