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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Long-QT syndrome and torsades de pointes

Cardiology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Escalate

Polymorphic VT with long QT may rapidly cause cardiac arrest. If pulseless, defibrillate under ALS; if a pulse remains, give IV magnesium, remove causes and use cardioversion for instability while arranging rate acceleration for recurrent pause-dependent torsades.

Synopsis

Measure QT accurately, distinguish congenital from acquired long-QT states and treat torsades without adding further QT-prolonging risk.

  • Measure QT from QRS onset to T-wave end in a lead with a clear T wave and correct for heart rate; automated QTc values require manual review.
  • Repeated QTc of 480 ms or more, a diagnostic score of 3.5 or more, or a pathogenic LQTS variant can establish congenital LQTS after acquired causes are addressed.
  • Torsades is polymorphic VT whose QRS axis twists around the baseline, usually in the setting of QT prolongation and pause dependence.
  • Acquired causes include QT-prolonging medicines, hypokalaemia, hypomagnesaemia, hypocalcaemia and bradycardia.
  • Current RCUK treatment is magnesium 8 mmol IV over 10 minutes, correction of causes, and consideration of isoprenaline or temporary pacing to raise heart rate.
  • Avoid amiodarone in torsades because it can prolong repolarisation further.
  • Congenital LQTS requires inherited-cardiac-condition review, trigger and medicine counselling, family screening and usually beta-blocker therapy.
  • An ICD is for selected high-risk patients; it does not replace beta-blockade, trigger control or correction of acquired factors.

Key red flags

Torsades morphology

Polymorphic broad complexes wax and wane in amplitude and appear to twist around the baseline, often after a short-long-short sequence.

Cardiac arrest

Unresponsiveness with absent normal breathing and no definite pulse converts the problem from torsades-with-a-pulse to VF/pulseless-VT ALS.

Investigation priorities

01
Repeat manual 12-lead QT measurementFirst step

Confirm that QT prolongation is real and reproducible.

Management branches

arrestPulseless torsades

The patient is unresponsive, not breathing normally and has no definite pulse.

  1. Start CPR, call the arrest team and attach a defibrillator.
  2. Treat as VF/pulseless VT with immediate unsynchronised defibrillation under the RCUK ALS algorithm.
  3. Give ALS drugs at the specified shock points while correcting potassium, magnesium and the precipitating cause.
  4. After ROSC, continue monitoring and arrange urgent cardiology/inherited-arrhythmia assessment.

Key medicines

Magnesium sulfateRCUK: 8 mmol IV over 10 minutes for polymorphic VT with QT prolongation.Give with ECG and blood-pressure monitoring; toxicity risk rises in severe renal impairment. This RCUK dose is the resuscitation regimen.
IsoprenalineRCUK adult bradyarrhythmia guidance gives a 5 micrograms/min IV infusion starting dose; in recurrent acquired pause-dependent torsades, titrate only with expert critical-care monitoring to increase heart rate.Can increase myocardial oxygen demand and provoke arrhythmia; specialist use only. It is generally avoided as a strategy for congenital catecholamine-triggered LQTS unless an expert identifies a specific indication.
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Sources and review status6 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • Resuscitation Council UK: Adult tachyarrhythmia algorithm, March 2026Magnesium dose, pacing/isoprenaline option and amiodarone avoidance.
  • ESC: 2022 ventricular arrhythmias guidelineLQTS risk assessment and prevention framework.
  • ESC: How to measure the QT intervalManual technique and diagnostic routes.
  • NHS: Long QT syndromeSymptoms, emergency advice, inherited testing and treatment overview.
  • NHS Genomics Education: Long-QT syndromeInherited phenotype and genomic pathway.
  • MHRA: Citalopram and escitalopram QT prolongationAdditive drug risk, contraindications and electrolyte/ECG monitoring.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom