What is long QT syndrome?

LQTS is a disorder of the heart’s electrical system. The electrical system controls the rate (speed) and rhythm of your heart. When it is working properly, your heart beats in a regular rhythm, at a normal rate. When it isn’t working properly, you have an arrhythmia. LQTS is a type of arrhythmia.

An EKG (electrocardiogram) measures and records the electrical activity that passes through the heart as it beats. Each part of the beat is mapped on a graph and has a name – P, Q, R, S, and T. Long QT is an abnormally long interval between the Q and T points of the pattern on an EKG.

If you have LQTS, your heart’s structure is perfectly normal, but you may have fast, chaotic heartbeats. The fast heartbeats may cause a sudden fainting spell or a seizure. In some cases, the heart can stop and cause sudden death. Long QT is treatable.


There are two types of long QT syndrome: 

  1. Inherited LQTS is the result of a gene mutation. Many genes associated with LQTS have been found, and hundreds of mutations have been identified. 
  2. Acquired LQTS can be caused by certain medications. Over 100 different medications can lengthen the QT interval (drug-induced long QT syndrome). Electrolyte imbalances such as low body potassium (hypokalemia) can also cause acquired LQTS. 

Some people with LQTS don’t have any symptoms. People who do have symptoms may experience unexplained fainting, unexplained seizures, and abnormal heartbeat (arrhythmia). Symptoms may be triggered by exercise or stress. If not detected and treated, LQTS could lead to sudden death in some cases.

Who is at risk?

If you have a family history of diagnosed LQTS or unexplained fainting, unexplained seizures, or sudden death in young people, you should advise your family doctor or healthcare provider as you may be at risk of inherited LQTS or other inherited rhythm disorders.

Children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents should be screened for LQTS.

If you are taking a medication that may lead to acquired LQTS, your healthcare practitioner will monitor your health and watch for signs of LQTS. 


LQTS can be an inherited or acquired condition. 

Certain medications can cause LQTS including some types of antidepressant and antipsychotic medications, antibiotics and diuretics. 

An electrolyte imbalance and low body potassium or sodium can trigger LQTS. Excessive vomiting, diarrhea or an eating disorder may all cause an electrolyte imbalance.


To diagnose LQTS your healthcare provider will review your medical history and give you a complete physical exam.

Prolonged QT intervals are detected with an EKG (electrocardiogram). This is a printed record of your heart's electrical activity that provides information about its rhythm, chambers, heart damage and other abnormalities.

Other tests may include:

LQTS is a difficult condition to diagnose because some people do not have a visibly prolonged QT interval on an EKG. If LQTS is suspected, it is important to be referred to a cardiologist who specializes in cardiac rhythm disorders for further testing.


LQTS is a treatable condition and your doctor may prescribe medication or surgery or may recommend lifestyle changes.


Beta-blockers are the most commonly prescribed medication. They slow your heart rate by reducing the effect of adrenaline on your heart. It’s important to talk to your doctor about the medications that work best for you and to follow instructions carefully.


In certain circumstances, you may need to have surgery on the nerves that regulate your heartbeat. If LQTS causes dangerously abnormal heart rhythms, you may need an implantable cardioverter defibrillator (ICD).


 Many people with LQTS need to make very few changes to their lifestyle, it their condition is properly treated and controlled. However, you might be required to make some adjustments. For example, certain sports or activities increase the risk of fainting or more serious events. It is important to talk to your cardiologist about how you can live a healthy, active lifestyle without risking further complications.

Related information 

Visit the Canadian SADS Foundation for publications about living with long QT syndrome.

To join or start an arrhythmia support group in your area go to the Heart Arrhythmia Alliance.

Managing your medications

Living Well with Heart Disease (PDF)


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