Long QT syndrome factsheet


Long QT syndrome (LQTS) is a heart rhythm disorder which can cause periods of abnormally fast or erratic heart rhythm called arrhythmias.

A QT interval is the time that it takes the heart muscle to contract and then recover. During this small period, the heart is at risk. If another electrical impulse arrives during the longer than normal QT interval, it can cause arrythmia. When arrythmia happens, there is less blood pumped from the heart, which can cause oxygen supply to drop. When there is a drop in oxygen to the body and brain, your child may experience a loss of consciousness or a fainting episode.

These episodes can be life-threatening if they are not recognised and treated quickly.

 Signs and symptoms

LQTS is a condition that people are born with, but it is usually only picked up in older children and young adults.

The most common symptoms of LQTS are:

  • fast or irregular heartbeats 
  • fainting or collapsing 
  • seizures

These symptoms, or episodes, commonly happen when your child is doing activities that increase their heart rate. This can include:

  • exercise, like swimming
  • emotional situations
  • responding to sudden loud noises. 


Many children do not show symptoms of LQTS, which makes it hard to diagnose early. Your child may be referred to a cardiologist (heart specialist) who can make a diagnosis based on their symptoms and after any appropriate tests including an echocardiogram (ECG). An ECG records your child’s heart activity to diagnose heart conditions and abnormal heart rhythms.  

Once your child is diagnosed with LQTS, it is very important that other direct family members (parents and siblings) are tested. Your child’s cardiologist or geneticist (genetic specialist) will let you know how other family members can be tested. 

If genetic testing finds a gene fault, other family members can be tested to find out if they carry the same gene change.

It is important to know that LQTS in the same family can affect family members very differently. Some family members with LQTS may never have any symptoms in their lifetime. Others, even within the same family, have more severe symptoms. 


The treatment for LQTS is aimed at reducing the risk of the arrhythmia from occurring. Lifestyle changes and medication are very effective and can be discussed and tailored to your child. 


The first treatment is usually a beta-blocker medication. These can include:

  • propranolol
  • atenolol
  • nadolol.

Beta-blockers help to control irregular heartbeats and can help slow the heart rate. 

Lifestyle modifications

Your child’s cardiologist will give you information about lifestyle changes and medication specific to your child. For most children, this includes avoiding strenuous activity, especially competitive sports, and swimming. In some cases, your child will need to avoid loud noises that may startle them or awake them when sleeping. 

Implantable cardioverter defibrillator

If beta-blockers are not effective in managing your child’s heart rhythm, your child may need to have an operation to implant an implantable cardioverter defibrillator (ICD). This device is like a pacemaker but is also able to deliver an electrical shock if it senses that the heart is beating in a potentially dangerous rhythm. This shock can help return the heart to normal rhythm and get it pumping again. 

Automatic External Defibrillator

An Automated External Defibrillator (AED) is a portable device that is used to deliver an electric shock to make the heart rhythm normal again. It is an external machine that has adhesive pads that need to be applied to your child’s chest for the shock to be delivered. The current devices are all preprogrammed to analyse the rhythm once the pads are applied. They will audibly instruct the user what action is needed. It is best to speak to your child’s cardiologist about whether this device is recommended.


Medication to avoid

It is important to note that there are many medications that may further lengthen the QT interval or increase the risk of the abnormal fast heart rhythm. Check with your child’s doctor or cardiologist before starting new medications.

Resources and more information

The Children's Hospital at Westmead

The Heart Centre for Children at Westmead

The Heart Centre for Children incorporates cardiology, cardiac surgery, cardiac research and the Edgar Stephens Ward at The Children's Hospital at Westmead. They offer comprehensive information about cardiac (heart) services provided to children.
Related Links
Australian Genetic Heart Disease Registry

Australian Genetic Heart Disease Registry

The Registry was established in 2007 to collect valuable information on Australian families with genetic heart disease to provide a better understanding of these conditions in Australia. They offer detailed information on conditions for patients.
Related Links


CredibleMeds®​​​​​​​ is an online resource, published in the United States, that promotes the safe use of medicines, including the QTdrugs list of drugs that should be avoided by those with long QT syndrome.
Related Links
Last updated Tuesday 12th December 2023


This factsheet is provided for general information only. It does not constitute health advice and should not be used to diagnose or treat any health condition.

Please consult with your doctor or other health professional to make sure this information is right for you and/or your child.

The Sydney Children’s Hospitals Network does not accept responsibility for inaccuracies or omissions, the interpretation of the information, or for success or appropriateness of any treatment described in the factsheet.

© Sydney Children’s Hospitals Network 2024