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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.

Electrical cardioversion and antiarrhythmic drugs

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

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For tachyarrhythmia with shock, severe hypotensive syncope, myocardial ischaemia, severe pulmonary oedema or immediately after ROSC, perform synchronised cardioversion. If the patient becomes pulseless, disable synchronisation and use the cardiac-arrest defibrillation pathway.

Synopsis

Deliver synchronised cardioversion safely, choose rhythm-specific energy and use emergency antiarrhythmics in their correct licensed or resuscitation context.

  • Synchronised cardioversion times the shock to the R wave to avoid energy delivery during ventricular repolarisation.
  • A conscious patient needs carefully titrated sedation or anaesthesia, but instability must not be allowed to worsen while waiting.
  • RCUK 2025 energies: AF at maximum defibrillator output; flutter/regular narrow tachycardia 70-120 J; VT with a pulse 120-150 J.
  • Re-enable and visually confirm synchronisation before every repeat shock; many defibrillators reset after delivery.
  • For persistent instability after up to three shocks, RCUK uses procainamide 10-15 mg/kg IV over 20 minutes (maximum 1 g) or amiodarone 300 mg IV over 10-20 minutes, followed by another shock.
  • For stable regular narrow tachycardia, the March 2026 RCUK adenosine sequence is 6 mg, 12 mg, then 18 mg as rapid IV boluses.
  • Emergency cardioversion is not delayed for anticoagulation; planned AF/flutter cardioversion requires a thromboembolism strategy when duration exceeds 48 hours or is uncertain.
  • Amiodarone has important lung, liver, thyroid, ocular, neurological and cardiac toxicity; long-term use needs explicit indication and monitoring.

Key red flags

Unstable tachyarrhythmia

Shock, syncope with severe or ongoing hypotension, myocardial ischaemia, severe pulmonary oedema or immediately post-ROSC favours immediate electricity.

Broad or irregular warning

Regular broad tachycardia is VT until proven otherwise; irregular broad tachycardia may be pre-excited AF or polymorphic VT and should not receive routine AV-nodal blockade.

Investigation priorities

01
12-lead ECGFirst step

Define rhythm, regularity, QRS width, QT, pre-excitation and ischaemia.

Management branches

unstableImmediate synchronised cardioversion

A perfusing tachyarrhythmia causes a life-threatening adverse feature.

  1. Call expert and anaesthetic help, perform ABCDE assessment, attach pads, monitor continuously and obtain IV access.
  2. Sedate or anaesthetise a conscious patient with careful haemodynamic planning when feasible without dangerous delay.
  3. Confirm synchronisation, then use maximum defibrillator output for AF, 70-120 J for flutter/regular narrow tachycardia, or 120-150 J for VT with a pulse; escalate and repeat to three shocks.
  4. If still unstable, give procainamide 10-15 mg/kg IV over 20 minutes (maximum 1 g) or amiodarone 300 mg IV over 10-20 minutes, then repeat synchronised cardioversion.
narrowStable regular narrow tachycardia

QRS is under 120 ms, rhythm regular and no adverse feature is present.

  1. Perform vagal manoeuvres while recording the ECG.
  2. If ineffective and the rhythm is not flutter and there is no pre-excitation concern, give adenosine 6 mg by very rapid IV bolus and flush.
  3. If unsuccessful give 12 mg, then 18 mg, each rapidly with continuous ECG recording and resuscitation capability.

Key medicines

AdenosineRCUK March 2026: 6 mg, then 12 mg, then 18 mg by very rapid IV bolus, each followed by a rapid flush. This algorithm-specific sequence differs from the cited product SmPC's licensed 3 mg, 6 mg, then 12 mg sequence.Do not use for irregular broad tachycardia or pre-excited AF. Give with continuous ECG and immediate resuscitation capability. The cited UK SmPC contraindicates bronchospastic chronic lung disease including asthma, long-QT syndrome, severe hypotension, decompensated heart failure, and sick-sinus or second-/third-degree AV block without a functioning pacemaker; avoid concurrent dipyridamole unless an expert-adjusted strategy is essential.
Procainamide10-15 mg/kg IV over 20 minutes, maximum 1 g.Continuous ECG and BP monitoring; stop or slow for hypotension, QRS widening or QT prolongation.
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Sources and review status7 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 advanced life support 2025Adverse features, shock energies and failed-cardioversion drugs.
  • Resuscitation Council UK: Adult tachyarrhythmia algorithm, March 2026Current adenosine sequence and stable tachyarrhythmia routes.
  • NICE NG196: Atrial fibrillation – recommendationsCardioversion and anticoagulation framework.
  • MHRA: Amiodarone monitoring reminderLong-term organ toxicity and 6-monthly thyroid/liver testing.
  • eMC: Amiodarone 30 mg/mL solution SmPCGeneral licensed IV regimen, monitoring and contraindications.
  • eMC: Eliquis 5 mg SmPCNVAF dose and reduction criteria.
  • eMC: Adenosine 3 mg/mL injection SmPCProduct-specific licensed dosing, contraindications and interactions, contrasted with the current RCUK algorithm.

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

If drug treatment fails, use synchronised cardioversion; consider verapamil or a beta-blocker only after rhythm, ventricular function and contraindications are assessed.
Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom