Long QT syndrome

Long QT syndrome is a condition that affects the rhythm of the heartbeat. It can cause fast, irregular heartbeats (known as arrhythmia), which may trigger a sudden fainting spell, or in some cases, if the heart does not regain its normal rhythm it may cause sudden death.

Key points:

  • Some people are born with a genetic mutation that puts them at risk of long QT syndrome. Certain medications and medical conditions can also cause long QT syndrome.
  • Long QT syndrome is treatable. You might need to take medications to keep your heart rhythm steady and regular. In some cases, surgery or an implantable device may be required.
  • If you are diagnosed with long QT syndrome, you need to avoid medications known to cause prolonged QT intervals. Sometimes, certain physical activities or stressors may also need to be avoided.

What is long QT syndrome?

Heartbeats are caused by electrical impulses that spread across the heart muscle, causing contractions of the heart muscle and the heart's pumping action. The electrical activity of the heart is measured using the test called ECG (electrocardigraph).  The ECG is recorded on paper, as spikes and dips called waves. By assessing the pattern of these waves, your doctor can gauge the rhythm and the rate of your heartbeat. In people with long QT syndrome, there is an extra-long, prolonged interval between two distinct points on the ECG.

(WCCHN, Canada, 2013)

Who is at risk of long QT syndrome?

You have an increased risk for long QT syndrome if other members of your family have the disorder. It is often inherited from a parent as a faulty gene (also called congenital long QT syndrome). 


Some medicines can trigger long QT syndrome (called drug-induced long QT syndrome). This usually happens in people with an inherited higher risk of developing it, such as those with slight genetic heart defects. Examples of medicines that may trigger long QT syndrome include:

  • antibiotics such as erythromycin, clarithromycin
  • antihistamines such as terfenadine (no longer available in NZ)
  • antidepressants such as citalopram, escitalopram, lithium 
  • heart medication such as flecainide, amiodarone, sotalol
  • domperidone
  • methadone.

Natural products, herbal supplements or dietary supplements 

An example of a natural product that causes long QT syndrome is Artemisia annua. It is also known as Qing hao, Sweet Annie or Sweet Wormwood. It is used as dried herbs or extracts in several natural health products available in New Zealand. New Zealand does not have a register of herbal medicines or an approval system for natural products so a complete list of products containing Artemisia annua dried herb or extract cannot be provided here. 
If you are at risk of prolonged QT interval, or are taking QT-prolonging medicines you should avoid products containing Artemisia annua. Carefully check the ingredients of any natural health product or dietary supplement before use. Ask your pharmacist for advice if you are unsure about the product.

See Drugs to avoid  (SADS, UK) or www.crediblemeds.org for a list of medicines that should be avoided.
Always check with your doctor or pharmacist if you are unsure of the safety of the medicines you have been prescribed. Also, these websites are non-New Zealand so some of the medicines names may differ.     

What are the symptoms of long QT syndrome?

Many people with long QT syndrome may not have any signs or symptoms. For those who do have symptoms, fainting, blackouts and irregular heart beat are the most common. These episodes can start at any age and may be triggered by:

  • stress
  • intense emotion (such as fright, anger, or pain)
  • a sudden, startling noise such as an alarm bell
  • strenuous exercise, particularly swimming
  • a slow heart rate during sleep.

However, there isn't always a trigger. Children who are born with long QT syndrome may have at least one episode of fainting by the time they are 10 years old. Others may just have 1 or 2 episodes of fainting as children, and then never have another episode again.

How is long QT syndrome diagnosed?

An ECG is the first test that you will have. You may need to repeat ECG recordings or have other tests, such as an exercise ECG.

How is long QT syndrome treated?

Long QT syndrome is most commonly treated with medicines called beta blockers. These work by slowing your heart rate. They do not cure long QT syndrome, but they have been shown to reduce or prevent the symptoms. Read more about beta blockers.

Depending on your symptoms and your risk of having a life-threatening arrhythmia, you may also need to have an implantable cardioverter-defibrillators (ICD) device fitted. These are devices placed inside the body to detect and correct abnormal heart rhythms. ICDs may be necessary for people who do not respond to beta blocker medicines.

If your long QT syndrome has been caused by medicines, these will be reviewed and adjusted so that you still receive the benefits without affecting your QT interval. 

Changes to your lifestyle

If properly treated and controlled, many people with long QT syndrome require very few changes to their normal lifestyle. However, you may need to make some adjustments to your lifestyle such as:

  • Discuss with your doctor if you need to avoid certain sports or activities that increase the risk of fainting or more serious events.
  • Always check the suitability of over-the-counter medicines and supplements with your doctor or pharmacist. Some of these may induce symptoms or react with medicines you may be taking to help reduce your risk of abnormal heart rhythms.
  • Some people may be advised to avoid sudden startling noises such as avoid using alarm clocks or turn your mobile phone off at night when you go to bed.
  • Let your doctor know if you have prolonged (longer than a day) or severe episodes of vomiting or diarrhoea. This can affect your sodium and potassium levels. You should discuss this situation with your doctor who may wish to prescribe oral rehydration supplements. These supplements can help to replenish sodium and potassium levels but should be used under medical supervision.  
  • Always let family and friends know about your condition, or wear a medic-alert bracelet, so that if you faint suddenly, they are aware to contact 111 immediately.  

Learn more

Long QT syndrome Starship Clinical Guidelines, 2018


  1. Artemisia annua and QT interval prolongation Medsafe, NZ, 2019
  2. Update on the diagnosis and management of familial long QT syndrome Heart, Lung and Circulation 2016;25:769-76
  3. Long QT Syndrome Circulation 2014;129: 1524-1529
  4. Drug-induced QT interval prolongation Dec 2011, Canterbury DHB, Drug Information Service
  5. Drug-induced QT prolongation and Torsades de Pointes – the facts Medsafe Update, NZ, 2010
  6. Drugs and the QTc interval Australian Prescriber 2002

Information for healthcare providers

Drugs to avoid www.sads.org.uk
Drugs categorised by their potential to cause QT prolongation 
Update on the diagnosis and management of familial long QT syndrome Heart, Lung and Circulation 2016;25:769-76
Long QT Syndrome Circulation 2014;129: 1524-1529
Drug-induced QT interval prolongation Dec 2011, Canterbury DHB, Drug Information Service
Drug-induced QT prolongation and Torsades de Pointes – the facts Medsafe Update, December 2010
Drugs and the QTc interval Australian Prescriber 2002

Credits: Health Navigator Editorial Team. Last reviewed: 20 Mar 2017