Long QT syndrome
This is an uncommon quirk of the heart's electrical system: the muscle takes longer than usual to recover between beats.
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Medicines commonly prescribed for Long QT syndrome
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 40 mgActive substance: propranololManufacturer: Kern Pharma S.L.Prescription requiredDosage form: TABLET, 40 mgActive substance: propranololManufacturer: Accord Healthcare S.L.U.Prescription requiredDosage form: TABLET, 10 mg propranololActive substance: propranololManufacturer: Atnahs Pharma Netherlands Bv.Prescription required
This is an uncommon quirk of the heart's electrical system: the muscle takes longer than usual to recover between beats. You can live with it your whole life and never notice, or you can collapse one day on a run — and that will be the first and only warning. The reassuring half of the story carries just as much weight: the condition shows up on an ordinary tracing of the heart, and straightforward treatment cuts the risk several-fold. Everything useful about this page comes down to one thing — finding out in time.
What the QT interval is and why a long one matters
On an electrocardiogram, the stretch from the Q wave to the end of the T wave shows how long the ventricles need to squeeze and then recharge before the next beat. When recharging drags on, the muscle cells come out of it at different moments: some are ready to respond, others are not. In that muddle a stray extra impulse can set off a chaotic ventricular rhythm known as torsade de pointes.
Most of the time the episode stops on its own within seconds and the person feels only a sharp wave of faintness, or blacks out. When it does not stop, the heart stops pumping. That is the mechanism behind sudden cardiac arrest in young, outwardly healthy people.
The length of the interval depends on how fast the heart is going, so what gets measured is a corrected figure, the QTc. The machine prints it automatically, but with borderline numbers a doctor measures it by hand: a few hundredths of a second decide whether there is a diagnosis.
How it shows itself
Most people who carry it have no complaints at all, and it turns up by chance — on a tracing done before surgery, for a sports club certificate, or while a relative is being checked. When there are signs, they look like this:
- Palpitations: sudden thumps in the chest, a sense that the heart stumbled or took off for no reason.
- A convulsive attack mistaken for epilepsy. The brain goes short of blood for a few seconds and the body answers with a seizure. It is a costly mistake: someone takes anticonvulsants for years while the problem sits in the heart.
- Deafness from birth together with fainting in a child: this is the rare and most severe form, and the deafness is not a coincidence but part of the condition.
- Fainting — the main signal, and the one most often waved away.
Fainting is common and the vast majority of episodes are harmless; the circumstances are what tell them apart. The harmless kind happens in a stuffy room, in a queue, at the sight of blood, after standing a long time; it is preceded by nausea, a grey veil across the vision and clammy sweat, and the person usually has time to sit down. What should worry you is different: fainting with no warning at all, during running or swimming, at a sudden noise such as an alarm clock or a doorbell, from fright or strong emotion, in sleep or immediately on waking. And separately, fainting in the first months after childbirth. Any of these deserves a tracing of the heart rather than the phrase "you're overtired".
When to call an ambulance
Immediately, if someone near you:
- is not breathing, or is breathing in rare gasps, and does not respond — this is cardiac arrest;
- has passed out and cannot be roused;
- has passed out while running, swimming or under any other exertion;
- is convulsing.
In Spain, Italy, Portugal, Poland and Ukraine an ambulance is called on the single European number 112. While it is on its way, cardiac arrest is decided by action: chest compressions and an automated external defibrillator if one is nearby. The device speaks its instructions aloud and will not shock anyone who does not need it. Relatives of someone with this diagnosis should take a resuscitation course.
How it is found
The first step is a tracing of the heart. After that a cardiologist or a heart rhythm specialist assembles the whole picture:
- Repeat tracings. The interval shifts from day to day, and one normal recording does not rule the condition out.
- Continuous monitoring — a small device records the rhythm for a day or longer, capturing sleep and exertion.
- An exercise test. The peak of effort is not the only thing that counts: how the interval behaves four minutes into recovery says a great deal.
- Blood tests — potassium, magnesium, calcium, thyroid function: each of these lengthens the interval on its own.
- Detailed family questions: sudden deaths at a young age, the unexplained drowning of a strong swimmer, a car crash with no obvious cause, a sudden infant death.
- Genetic testing. It finds the fault in roughly three quarters of people with an evident syndrome. A negative result does not undo the diagnosis, while a positive one lets relatives be checked precisely.
Why the interval stretches
The inherited form comes from changes in the genes for ion channels — the gates in the membrane of heart cells. Half the children of a carrier inherit the trait. There are several variants, and this is not an academic nicety: in one, the rhythm is thrown by exertion and above all by swimming; in another, by a sharp noise or a shock; in a third, attacks come during sleep. That is why advice to two people with the same diagnosis can differ.
The acquired form is considerably more common than the inherited one. It is brought on by:
- medicines — the commonest cause, dealt with separately below;
- low potassium, magnesium or calcium: after vomiting and diarrhoea, on diuretics, in eating disorders;
- a slow pulse and problems with conduction through the heart;
- an underactive thyroid gland;
- bleeding into the brain and severe stroke;
- hypothermia and serious damage to the heart muscle.
Trouble usually arrives at a junction: a hidden inherited tendency, a newly prescribed drug, and a bout of gastroenteritis that strips out potassium. On its own, not one of the three would have done anything.
Medicines worth knowing about
The list of drugs that lengthen the interval is long and constantly updated. Widely used ones on it include certain anti-arrhythmic drugs, macrolide and fluoroquinolone antibiotics, antifungals, several anti-sickness medicines, some antidepressants and antipsychotics, antimalarials, older allergy remedies and methadone. This is not a lifelong ban — it simply means each prescription is discussed rather than issued out of habit.
- Any new product, including over-the-counter remedies, herbal preparations and supplements, only after a check: a doctor or pharmacist can consult a dedicated list.
- Two drugs from the risk group at once is avoided. So is another trap: medicines that slow each other's clearance, grapefruit juice among them, push blood levels above what was intended.
- Carry a note of the diagnosis — in a wallet, on a phone, on a bracelet. In an emergency there will be no time to ask.
- If a risky drug is genuinely necessary and nothing can replace it, it is given with tracings to keep watch.
What is offered for protection
Treatment is chosen by risk: whether there have been blackouts, how long the interval is, which variant it is, what the family history says.
- Beta blockers are the mainstay for most people. They blunt the heart's response to a surge of adrenaline, removing the trigger itself. They are taken for years, and regularity is what counts: a missed dose leaves you unprotected, and stopping abruptly on your own is dangerous.
- An implantable cardioverter defibrillator — a device the size of a matchbox stitched under the skin of the chest; it watches the rhythm and breaks a dangerous episode with a shock. It is offered to those who have survived a cardiac arrest, whose blackouts continue on treatment, or whose calculated risk is especially high.
- Surgery on the nerves running to the heart (left cardiac sympathetic denervation) — for when drugs are not enough and a defibrillator is unsuitable or fires too often.
- Removing the cause in the acquired form: stopping the culprit drug, replacing potassium and magnesium, treating the thyroid — often that is all it takes.
- A pacemaker if the trouble lies in too slow a pulse.
Living with it, and what matters for the family
The day-to-day rules here are concrete, and most of them are about triggers.
- Water. No swimming alone and no diving; whoever is with you must know the diagnosis and be able to pull you out and resuscitate. For the commonest variant water is the leading trigger, and the drowning of a strong swimmer in a family history usually means an attack rather than an accident.
- Sport. Blanket bans are imposed less often than they used to be, but the amount and type of exercise is settled with a cardiologist, not decided alone.
- Sudden noise. A loud alarm clock, a doorbell, a phone by the pillow are a direct trigger for some people; alerts are set soft and rising.
- Potassium. Vegetables, pulses, fruit, and supplements if a doctor prescribes them. With vomiting or diarrhoea, rehydration solutions and a call to the doctor.
- Fever is brought down rather than waited out: heat lengthens the interval.
- What should not be there: energy drinks, large doses of caffeine, cocaine and amphetamines.
- People around you. School, coach and employer should know the diagnosis, and you should know where the defibrillator in your building is.
- Pregnancy and the first months after birth are a period of higher risk. Beta blockers are usually continued, but care is planned in advance with a cardiologist.
And the most important part about family. If you have the diagnosis, your parents, brothers, sisters and children need a tracing of the heart, and where the genetic fault is known they should be offered a targeted test. Half of close relatives may turn out to carry it without ever having felt a thing. Testing them is not a formality: this is precisely how you prevent the sudden death that a family afterwards describes with the words "he was perfectly healthy".
Online consultation
A remote appointment is useful at several stages. Before a diagnosis, to unpick a blackout: the doctor will go through the circumstances, separate the harmless kind from the worrying kind, look at a tracing you already have, and say whether monitoring, an exercise test and a face-to-face visit to a rhythm specialist are needed. After a diagnosis, online is where the everyday business of living with the syndrome gets handled: the safety of any new medicine or supplement, how the beta blocker is tolerated, potassium and magnesium results, planning a pregnancy, preparing for an operation or dental work. A frequent task of its own is explaining to relatives why they need testing. What an online appointment does not replace is the ambulance: for a blackout during exertion, a seizure or a cardiac arrest, call the emergency service.
This material is for information only and does not replace medical advice.
Consult with a doctor about Long QT syndrome
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Online doctors for Long QT syndrome
Discuss your symptoms and possible next steps for Long QT syndrome with a doctor online.
