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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Long QT = QTc >450 ms (males) or >460 ms (females). QTc >500 ms significantly increases risk of TdP
- Congenital: ion channelopathies (Romano-Ward = AD, Jervell-Lange-Nielsen = AR + sensorineural deafness)
- Acquired (far more common): drugs (antiarrhythmics, macrolides, antipsychotics, methadone), hypokalaemia, hypomagnesaemia, hypocalcaemia
- Torsades de Pointes (TdP): polymorphic VT with undulating QRS axis — treated with IV magnesium 2 g and overdrive pacing
- Congenital LQTS: beta-blockers reduce events; ICD if high risk; avoid QT-prolonging drugs
Overview
Long QT syndrome (LQTS) refers to a prolongation of the QT interval on ECG representing delayed ventricular repolarisation. This creates a vulnerable period for triggered activity, predisposing to the polymorphic ventricular tachycardia Torsades de Pointes (TdP), which may degenerate into ventricular fibrillation and sudden death. Congenital LQTS is caused by mutations in cardiac ion channel genes (15+ subtypes identified; LQT1, LQT2, and LQT3 account for 90%). Acquired LQTS is far more common and results from drugs, electrolyte disturbances, or metabolic conditions. Always correct the QT for heart rate using Bazett formula: QTc = QT/√RR.
Epidemiology
Congenital LQTS affects approximately 1 in 2,000–5,000 people. It is an important cause of sudden cardiac death in young people and children. Acquired LQTS is much more common and is one of the most frequent causes of drug withdrawal from the market. Key drug classes include: class Ia/III antiarrhythmics (amiodarone, sotalol), macrolide antibiotics (erythromycin, clarithromycin), fluoroquinolones, antipsychotics (haloperidol, pimozide), SSRIs, methadone, domperidone, and ondansetron.
Clinical Features
Symptoms
Syncope — often triggered by exercise (LQT1), auditory stimuli/emotion (LQT2), or sleep/rest (LQT3)
Palpitations (preceding syncopal episodes)
Seizures (misdiagnosed as epilepsy — prolonged VT causing cerebral hypoperfusion)
Sudden cardiac death (may be first presentation)
Family history of unexplained sudden death or drowning at young age
Congenital deafness (Jervell-Lange-Nielsen syndrome)
Signs
Usually no clinical signs at rest
Bradycardia (LQT3 — Na⁺ channel mutation)
Signs detected on ECG: prolonged QTc, T-wave morphology abnormalities
Investigations
First-line
12-lead ECGMeasure QTc (Bazett: QT/√RR). QTc >450 ms (male) or >460 ms (female). T-wave morphology helps identify subtype: LQT1 = broad-based T; LQT2 = notched/bifid T; LQT3 = late-onset peaked T with long ST
BloodsK⁺, Mg²⁺, Ca²⁺ (exclude acquired causes), TFTs
Medication reviewIdentify all QT-prolonging drugs (cross-reference with CredibleMeds.org)
Second-line
Exercise stress testQT response to exercise — LQT1 shows failure to shorten QT appropriately with exercise
Ambulatory ECGQT variation with heart rate, arrhythmia detection
Specialist
Genetic testingIdentify pathogenic variant (LQT1-3 account for 90%). Enables cascade family screening
Epinephrine QT stress testParadoxical QT prolongation with low-dose adrenaline suggests LQT1
1
All patients
- Avoid all QT-prolonging drugs (CredibleMeds.org for up-to-date list)
- Correct electrolyte abnormalities (maintain K⁺ >4.0, Mg²⁺ >0.8 mmol/L)
- Genetic counselling and cascade family screening
2
Congenital LQTS — beta-blockers
- First-line for LQT1 and LQT2: nadolol or propranolol (non-selective beta-blockers preferred over selective)
- LQT3: mexiletine (Na⁺ channel blocker) may be beneficial; beta-blockers less effective
- Lifestyle: LQT1 avoid strenuous exercise (especially swimming); LQT2 avoid loud alarms, emotional stress; LQT3 avoid excessive sleep without monitoring
3
High-risk patients — ICD
- Survivors of cardiac arrest
- Recurrent syncope despite beta-blocker therapy
- QTc >500 ms with high-risk genotype
- Left cardiac sympathetic denervation (LCSD) — alternative for patients not suitable for ICD or with recurrent ICD shocks
4
Acute Torsades de Pointes
- IV magnesium sulphate 2 g over 10 min (first-line, even if Mg²⁺ normal)
- Overdrive pacing (increase HR to shorten QT)
- Isoprenaline infusion if pacing not immediately available
- DO NOT give amiodarone (prolongs QT further)
Complications
- Torsades de Pointes: Polymorphic VT that may self-terminate or degenerate into VF
- Sudden cardiac death: Especially in young people — often first presentation of congenital LQTS
- Misdiagnosis as epilepsy: Syncope from TdP may present as apparent seizures
UKMLA Exam Tips
- 1TdP = polymorphic VT + long QT. Treatment = IV magnesium. Do NOT give amiodarone (it prolongs QT)
- 2Young person + syncope during exercise → think LQT1. During emotional stress/alarm → think LQT2. During sleep → think LQT3
- 3Jervell-Lange-Nielsen = long QT + congenital sensorineural deafness (autosomal recessive)
- 4Common QT-prolonging drugs: amiodarone, sotalol, erythromycin, clarithromycin, haloperidol, methadone, domperidone
- 5Always check QTc when prescribing known QT-prolonging drugs — QTc >500 ms = high risk of TdP
- 6Bazett formula: QTc = QT/√RR. Know how to calculate it from an ECG strip
practicetest your knowledge on long qt syndromeApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — cardiovascular and beyond.
open q-bank