Long QT syndrome

Physical exam

Long QT syndrome (LQTS) is a rare inherited condition that can cause abnormal heart rhythms (arrhythmias). It affects around 1 in 2,000 people.

These arrhythmias are caused by a delay in your electrical system, which keeps you heart pumping, known as ‘prolonged repolarisation’.

Prolonged repolarisation shows up on an ECG as a lengthened QT interval, which is part of the heartbeat cycle.

What are the symptoms of LQTS?

The symptoms of LQTS vary from person to person but the most common are blackouts and palpitations. These are caused by abnormal heart rhythms. Other symptoms will depend on:

  • the type of LQTS you have
  • your gender
  • your age
  • the length of QT interval (part of the heartbeat cycle).

What causes LQTS?

LQTS is a channelopathy and can be caused by certain medications you’re taking for other conditions. It’s also an inherited heart condition which means it can also be passed down from your parents through your genes.

Types of LQTS

There are two different channels that can affect the electrical system in your heart:

  • potassium channel LQTS, which carries the risk of sudden death if you are startled or awoken suddenly
  • sodium channel LQTS, which increases your risk of sudden death when you’re sleeping.

In most cases, LQTS delays the flow of potassium ions out of your heart’s cells. However, for some people, the sodium channels are affected and too many sodium ions are allowed into your heart’s cells. Both types can lead to dangerous arrhythmias.

What are the risks for LQTS?

If you have LQTS, abnormal heart rhythms can happen in response to:

  • stress
  • a sudden noise
  • strenuous exercise (particularly swimming)
  • a slow heart rate during sleep. 

An abnormal heart rhythm may return to normal but, if it doesn’t, your risk of sudden cardiac death is high. If someone is unconscious and not breathing, call 999 and start cardiopulmonary resuscitation (CPR) until medical help takes over. If there’s someone nearby, ask them to find a public access defibrillator.

Your risk of sudden cardiac death is higher if you have:

  • blackouts
  • a very long QT interval on your ECG
  • sodium channel mutations
  • previously had a cardiac arrest.

It’s important to speak to your doctor if you have any questions or concerns. They may advise you to avoid competitive sport, which can be difficult if you’re a very active person, or used to exercising at a high level. Your doctor will be able to explain the activities where your risk is lower.

How is LQTS diagnosed?


You’ll be given an ECG to monitor the electrical activity of your heart. Sometimes this test needs to be done more than once and further tests, such as an exercise ECG, can help confirm your diagnosis.

As LQTS is sometimes inherited, you may also be invited for genetic testing  to screen for any faulty genes that are linked with the condition. Your immediate family members (such as your parents, siblings and your children) may also be invited for an assessment.

What treatments are available for LQTS?

You’re likely to be given medication and, if you’re at risk of a life-threatening arrhythmia, you may also need a pacemaker or ICD fitted or have surgery to disrupt the nerves that release adrenaline and other natural chemicals into your heart.

If you have a potassium channel LQTS, your doctor may also prescribe potassium supplements or suggest you increase your uptake of potassium-rich foods like bananas, vegetables and pulses.

Can I live a normal life with LQTS?

With regular check-ups, you can continue to live a normal and active life. However, you should be aware that:

  • If you need an ICD, there may be things to plan for, such as not driving for a little while after having it fitted.
  • You may have to give up some competitive sports, but your doctor can advise you on physical activity which comes with less risk.
  • You may have to take potassium supplements or increase the amount of potassium-rich food in your diet.
  • Some over-the-counter medicines or supplements can increase your symptoms so you should discuss these with your doctor before taking them.
  • Prolonged (longer than a day) or severe episodes of vomiting or diarrhoea can affect your sodium and potassium levels. You should discuss this 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.

Read about the Rosser family and how they’ve been affected by Long QT syndrome.

Genetic Information Service

If you have further questions about inherited heart conditions, call our Genetic Information Service on 0300 456 8383. Lines are open from 9am to 5pm, Monday to Friday (charged at a rate similar to 01 or 02 calls).

Inherited abnormal heart rhythms booklet

This booklet explains what an inherited abnormal heart rhythm is, genetic screening, testing and implications for your family and future generations. 

Order or download now

Our scientists are helping to beat heartbreak

Your donations help us fund hundreds of top scientists all over the UK, working on more than a thousand different research projects.

They're finding new, better treatments for people with heart and circulatory diseases, and developing new ways to better prevent or diagnose them.

Donate to help beat heartbreak

Want to know more?

Order or download our publications: