Long QT syndrome is a heart rhythm condition in which the heart’s electrical system takes longer than normal to reset between beats. Most people have no symptoms, but it can occasionally trigger a dangerous fast heartbeat that causes fainting, seizures, or — rarely — sudden cardiac arrest. It is important because it can be identified on an ECG and treated, greatly reducing risk. In Singapore, care is guided by a cardiologist or a heart rhythm specialist (electrophysiologist).
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In a medical emergency, or for severe or sudden symptoms such as breathing difficulty, chest pain, fainting or stroke signs, call 995 immediately.
Every heartbeat is driven by a wave of electrical activity that spreads across the heart muscle and then recharges before the next beat. In long QT syndrome this recharging phase is prolonged, which shows up as a longer “QT” interval on an electrocardiogram (ECG). While the condition sounds alarming, understanding your triggers, taking any prescribed medicines reliably, and screening close relatives can make everyday life safe and normal for most people.
What long QT syndrome is
Long QT syndrome is a disturbance of the heart’s electrical system. After each beat, the heart’s cells need to recover their electrical charge before they can fire again. When this recovery takes longer than it should, the heart becomes briefly unstable and can, in some circumstances, tip into a very fast and chaotic rhythm. This abnormal rhythm may cause a sudden loss of consciousness, a seizure-like episode, or, uncommonly, cardiac arrest. The key message is that long QT is both identifiable — usually on a simple ECG — and treatable, so recognising it is the most important step.
Symptoms
Many people with long QT syndrome feel completely well and have no symptoms at all; the condition is sometimes discovered by chance on an ECG done for another reason. When symptoms do occur, the most important is fainting or a blackout, particularly during physical exertion, strong emotion or fright, or in response to a sudden loud noise such as an alarm. Some people have palpitations — a fluttering or pounding sensation in the chest — and occasionally an episode looks like a seizure. A family history of unexplained fainting, drowning, near-drowning, or sudden death at a young age is an important clue that should always be mentioned to a doctor.
Causes
There are two broad forms. Inherited (genetic) long QT is present from birth and results from differences in the genes that control the heart’s electrical channels; it can run in families. Acquired long QT develops later and is usually related to certain medicines that lengthen the QT interval, or to low levels of blood salts such as potassium and magnesium. A wide range of medicines — used for the heart and for many unrelated conditions — can prolong the QT in susceptible people, which is why it matters to tell every doctor and pharmacist about your condition so these can be reviewed or avoided.
Who is at risk
The main risk factor for the inherited form is a family history of long QT syndrome, or of unexplained fainting, seizures, drowning, or sudden death at a young age among close relatives. For the acquired form, risk is higher in people taking QT-prolonging medicines, in those with low blood potassium or magnesium (for example after significant vomiting, diarrhoea, or certain diuretics), and in some other medical conditions. Sometimes inherited and acquired factors combine, so a medicine or a low salt level unmasks an underlying tendency.
How it is diagnosed
The starting point is an ECG, which records the heart’s electrical activity and shows the length of the QT interval. Because the QT can vary, your doctor may repeat the ECG, record it during or after exercise, or ask you to wear a portable monitor for a period so that the rhythm can be captured over daily activities. Genetic testing may be offered, especially where an inherited form is suspected, and can help identify the specific type and guide advice. When a person is diagnosed, screening of close relatives — often with an ECG and sometimes genetic testing — is recommended, because affected family members may not yet have symptoms.
Treatment
Treatment is tailored to the individual and aims to keep the heart’s rhythm steady and reduce the chance of a dangerous episode. Medicines, most commonly beta-blockers, are a mainstay for many people and help calm the heart’s response to exertion and stress. Just as important is avoiding triggers and QT-prolonging medicines: your care team can provide a list of substances to avoid, and correcting low blood salts such as potassium and magnesium removes a reversible cause. For people judged to be at higher risk, an implantable cardioverter defibrillator (ICD) — a small device that can detect and stop a dangerous rhythm — may be recommended. Your cardiologist or electrophysiologist will also give personalised lifestyle and exercise guidance, as activity advice differs from person to person. Where an acquired cause is found, treating or removing it is part of the plan.
Living with it and self-care
Living well with long QT syndrome centres on a few reliable habits. Take any prescribed heart medicines exactly as directed and do not stop them suddenly, as this can itself be risky. Carry a written list of medicines to avoid, and show it whenever you see a new doctor, dentist, or pharmacist — including for minor illnesses, when some over-the-counter or prescribed treatments may not be suitable. Encourage close relatives to be screened, since they may be affected without knowing. Follow your specialist’s advice on exercise and triggers, keep well hydrated, and replace lost salts sensibly during illness with vomiting or diarrhoea. Finally, make sure the people around you — family, friends, and colleagues — know what to do if you collapse: to call 995, start CPR, and use an AED if one is available. Learning CPR yourself is a valuable step for the whole family.
When to seek emergency help
Call 995 immediately and begin CPR if someone collapses and is not breathing normally, sending another person to fetch the nearest AED. Seek urgent medical assessment for any unexplained faint or blackout, particularly if it happens during exercise or strong emotion, and arrange prompt review if a close relative dies suddenly and unexpectedly at a young age. Do not stop prescribed heart medicines on your own, and always tell doctors you have long QT so that QT-prolonging medicines can be avoided.
Common questions
Can I still exercise if I have long QT syndrome?
Many people can stay active, but the right level and type of activity vary from person to person. Your cardiologist or electrophysiologist will give tailored advice based on your form of long QT and your risk, so it is important to ask before taking up new or competitive sport.
Is long QT syndrome inherited?
It can be. The inherited form is present from birth and may run in families, which is why screening of close relatives is recommended. There is also an acquired form linked to certain medicines and low blood salts, which is not passed on but can be triggered later in life.
Why do doctors need to know about my condition before prescribing?
Many common medicines, for the heart and for unrelated illnesses, can lengthen the QT interval. Telling every doctor, dentist, and pharmacist allows them to check each treatment and choose safer alternatives where needed.
Will I need a defibrillator?
Not everyone does. An implantable defibrillator is usually considered only for people assessed to be at higher risk, for example those who have already had a serious rhythm episode. Your specialist will weigh the benefits and risks with you.
Can long QT syndrome be cured?
It is generally a lifelong condition rather than one that is cured, but it can be managed very effectively. With the right medicines, trigger avoidance, and follow-up, most people lead full and active lives. Where the cause is acquired, correcting it can resolve the problem.
Related guides
Sources
- National Heart Centre Singapore
- Singapore Heart Foundation
- HealthHub
- Heart Rhythm Society