Long QT Syndrome

Definition

Long QT syndrome (LQTS) is an inherited disorder of the ion channels that control the heart's electrical activity — a channelopathy. The heart muscle itself is structurally normal; the fault is in the electrical recovery, or repolarisation, of each beat.^3,4

The delay is visible on an ECG as a prolonged QT interval, corrected for heart rate (QTc). It matters because prolonged repolarisation allows a particular kind of abnormal beat to trigger torsades de pointes, a fast ventricular rhythm that causes sudden loss of consciousness and can progress to cardiac arrest.^1,2

Roughly one person in 2,000 carries the condition, and it is one of the recognised causes of unexplained sudden death in the young.^3,4 It is also one of the most treatable.

Pathophysiology

Why the reset is delayed

Repolarisation depends on potassium flowing out of heart cells while sodium and calcium stop flowing in. Most LQTS is caused by a variant in one of three genes: KCNQ1 and KCNH2, which reduce potassium currents, or SCN5A, which allows a small sodium current to persist when it should have stopped.^3,10 All three leave the cell taking longer to return to its resting state.

Why the genotype changes the advice

The three common subtypes behave differently, and this is practical rather than academic:^3,4

• LQT1 (KCNQ1) — events are typically triggered by exercise, and swimming is a characteristic trigger.
• LQT2 (KCNH2) — events are typically triggered by sudden startle: an alarm clock, a telephone, a shout.
• LQT3 (SCN5A) — events more often occur at rest or during sleep.

Genotype also predicts how well beta blockers work, which is why genetic testing is part of standard care rather than an optional extra.^6,10

Acquired QT prolongation

The QT interval can also be prolonged by medications, by low potassium or magnesium, and by starvation or severe illness.^1,11 Many commonly prescribed drugs are involved — some antibiotics, antipsychotics, antidepressants and anti-nausea medicines among them — and a person with congenital LQTS is far more vulnerable to that additional effect.¹¹

Symptoms

Many people have no symptoms at all and are identified only through family screening or an incidental ECG.⁴ When symptoms occur they are:

• Fainting (syncope), typically sudden and without the usual warning of light-headedness or nausea. The pattern is often characteristic — mid-exercise, or immediately after a startle.^3,4
• Seizure-like episodes, caused by lack of blood flow to the brain, which is why some people with LQTS are first diagnosed with epilepsy.⁴
• Palpitations, less commonly.
• Cardiac arrest, which may be the first presentation. Uncommon, but the reason the condition is taken seriously.^1,2

Fainting during exercise or immediately after a fright should never be dismissed as an ordinary faint. Ordinary faints have warning symptoms and happen when standing still or standing up, not at peak exertion.⁴

Diagnosis

• A 12-lead ECG with careful manual measurement of the QT interval, corrected for heart rate. Automated readings are unreliable in this setting and should be checked by hand.⁴
• Repeat ECGs. The QT interval varies from day to day, and a single normal ECG does not exclude the diagnosis — a common source of false reassurance.^3,4
• Exercise testing, looking particularly at how the QT behaves in the first minutes of recovery.⁴
• The Schwartz score, which combines ECG findings, symptoms and family history into a probability rather than a yes-or-no answer.³
• Genetic testing, which identifies a causative variant in most clinically definite cases and allows cascade screening of relatives.¹⁰
• Family assessment. Inheritance is usually autosomal dominant, so first-degree relatives are offered testing — often the most valuable single consequence of a diagnosis.^1,10

Management

Treatment aims to prevent arrhythmia, and it works. Untreated symptomatic LQTS carries a substantial risk of events; with treatment that risk falls considerably.^5,6

• Beta blockers, the foundation of treatment. Nadolol and propranolol are more effective than metoprolol in this condition — a difference that matters, because beta blockers are not interchangeable here.^5,6
• Avoiding QT-prolonging medicines, checked against a maintained list rather than from memory. This applies to over-the-counter and dental prescriptions too.¹¹
• Correcting potassium and magnesium, and taking illnesses with vomiting or diarrhoea seriously because of the electrolyte loss.¹
• Trigger-specific advice by genotype — swimming supervision in LQT1, removing startling alarms in LQT2.^3,4
• An implantable defibrillator (ICD) for those who have had a cardiac arrest or who continue to have events on treatment. It is not first-line for most people.^1,2
• Left cardiac sympathetic denervation, a surgical option that reduces events in high-risk patients who cannot be controlled medically.⁷

Exercise and sport

This has changed, and older advice is still circulating. People with LQTS were once disqualified from competitive sport almost universally. Long-term follow-up of athletes who continued to play, under treatment and with a management plan, showed event rates far lower than that blanket policy assumed.^8,9 Current European guidance supports shared decision-making rather than automatic exclusion, with the decision resting on genotype, symptom history, QTc and treatment adherence.^2,12

This is a cardiology decision, not a physiotherapy one. But it means the answer to "can I exercise?" is now usually yes, with conditions — and someone told otherwise ten years ago may be living with an out-of-date restriction.^9,12

Co-morbidities and complications

• Torsades de pointes and ventricular fibrillation, the central risks.^1,2
• Misdiagnosis as epilepsy, which delays correct treatment sometimes for years.⁴
• Deafness in Jervell and Lange-Nielsen syndrome, a rare recessive form combining congenital deafness with a markedly prolonged QT and higher risk.³
• Anxiety, in those diagnosed and in parents of diagnosed children — well recognised and frequently under-addressed.^4,9
• ICD complications where a device is fitted, including inappropriate shocks.²

Medications

Listed for recognition. Prescribing sits with the cardiologist or electrophysiologist.

• Nadolol — often preferred, given once or twice daily.⁶
• Propranolol — also effective; shorter acting.^5,6
• Metoprolol — less effective in LQTS and generally avoided where alternatives exist.⁶
• Mexiletine — used selectively in LQT3, where it addresses the persistent sodium current directly.⁴
• Potassium and magnesium supplements where levels are low.¹

Beta blockers in LQTS are taken for prevention, not for symptoms, so there is nothing to feel on a good day and stopping them feels harmless. It is not.⁵

Prognosis

With diagnosis and treatment the outlook is good. Beta blockade substantially reduces cardiac events, and most treated people live a normal life span with normal activity.^5,6

Risk is graded rather than uniform, estimated from QTc, genotype, sex, age and event history — a QTc above 500 ms, a previous arrest and LQT2 or LQT3 genotypes all raise it.^2,3 Risk is highest in those who are undiagnosed, which is the argument for family screening: the treatment works, so finding people is the intervention.^1,10

Living with it

• Carry the diagnosis in writing. A card or phone note naming the condition and the medication prevents a QT-prolonging drug being given in an emergency department or a dental chair.¹¹
• Tell the people you swim and train with, particularly in LQT1. Supervision is a specific recommendation, not general caution.^3,4
• Treat vomiting and diarrhoea properly. An illness that drops potassium is a genuine risk, and a normally trivial event becomes worth managing.¹

Families often find the hardest part is not the medication but deciding how much to restrict a child. That conversation belongs with the cardiologist, and current guidance is considerably less restrictive than it was.^9,12

Role of the physiotherapist

The arrhythmia is not a physiotherapy problem, and we do not manage it. What we contribute sits either side of the cardiology decision:

• Recognising the pattern and referring. Fainting at peak exertion, or immediately after a startle, is a red flag — not a vasovagal faint and not deconditioning. Exercise professionals are sometimes the first to hear about it.⁴
• Delivering the exercise a cardiologist has permitted. Where sport or training has been cleared, often after years of restriction, a supervised graded programme is how confidence returns. This is now a common referral, because the guidance changed.^9,12
• Working within the plan. We ask for the QTc, the genotype if known, the current beta blocker and any activity limits in writing. Beta blockade blunts heart rate, so intensity is prescribed by perceived effort — a heart-rate zone calculated from age is meaningless on nadolol.^5,6
• Emergency preparedness. Knowing where the defibrillator is, and that staff can use it, is a reasonable expectation of any facility training someone with an arrhythmia risk.²

We do not clear anyone for sport, adjust beta blockers, or interpret a QT interval. Bring the cardiologist's letter — it determines what we can do.

Part 1 · References

1. Priori SG, Blomström-Lundqvist C, Mazzanti A, et al. 2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J 2015;36(41):2793–2867.
2. Zeppenfeld K, Tfelt-Hansen J, de Riva M, et al. 2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Eur Heart J 2022;43(40):3997–4126.
3. Schwartz PJ, Crotti L, Insolia R. Long-QT syndrome: from genetics to management. Circ Arrhythm Electrophysiol 2012;5(4):868–877.
4. Wilde AAM, Amin AS, Postema PG. Diagnosis, management and therapeutic strategies for congenital long QT syndrome. Heart 2022;108(5):332–338.
5. Moss AJ, Zareba W, Hall WJ, et al. Effectiveness and limitations of beta-blocker therapy in congenital long-QT syndrome. Circulation 2000;101(6):616–623.
6. Abu-Zeitone A, Peterson DR, Polonsky B, McNitt S, Moss AJ. Efficacy of different beta-blockers in the treatment of long QT syndrome. J Am Coll Cardiol 2014;64(13):1352–1358.
7. Schwartz PJ, Priori SG, Cerrone M, et al. Left cardiac sympathetic denervation in the management of high-risk patients affected by the long-QT syndrome. Circulation 2004;109(15):1826–1833.
8. Johnson JN, Ackerman MJ. Return to play? Athletes with congenital long QT syndrome. Br J Sports Med 2013;47(1):28–33.
9. Tobert KE, Bos JM, Garmany R, Ackerman MJ. Return-to-play for athletes with long QT syndrome or genetic heart diseases predisposing to sudden death. J Am Coll Cardiol 2021;78(6):594–604.
10. Ackerman MJ, Priori SG, Willems S, et al. HRS/EHRA expert consensus statement on the state of genetic testing for the channelopathies and cardiomyopathies. Europace 2011;13(8):1077–1109.
11. Woosley RL, Heise CW, Gallo T, Woosley RD, Romero KA. QTdrugs list. CredibleMeds, AZCERT Inc., Tucson AZ; accessed 1 September 2026.
12. Pelliccia A, Sharma S, Gati S, et al. 2020 ESC Guidelines on sports cardiology and exercise in patients with cardiovascular disease. Eur Heart J 2021;42(1):17–96.