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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.

Bradycardia and heart block

Cardiology · UK scope · Sources checked 25 Aug 2026 · Clinical review pending

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Bradycardia with shock, syncope, myocardial ischaemia, severe heart failure or immediately post-ROSC needs immediate RCUK treatment. High-grade AV block with a broad QRS is a pacing/chronotrope emergency: RCUK says not to give atropine because it is ineffective and may worsen the block.

Synopsis

Classify bradyarrhythmias, identify imminent asystole and use atropine, chronotropic infusions and pacing in the correct conditional branch.

  • Bradycardia is a rate, not a diagnosis; athletes and sleep can be physiological, while symptoms and conduction level determine urgency.
  • First-degree AV block: every P conducts with a constant PR over 200 ms.
  • Mobitz I: progressive PR lengthening before a dropped QRS; Mobitz II: fixed PR intervals with sudden non-conducted P waves.
  • A 2:1 AV block cannot be reliably called Mobitz I or II from the ratio alone; QRS width and specialist assessment help localise it.
  • Complete AV block shows independent atrial and ventricular activity; a slow broad escape implies distal disease and higher asystole risk.
  • RCUK life-threatening features are shock, syncope, myocardial ischaemia, severe heart failure and immediately post-ROSC.
  • With adverse features give atropine 500 micrograms IV, repeating every 3-5 minutes to a total of 3 mg—except cardiac transplant or high-grade broad-QRS AV block.
  • If response is inadequate, use transcutaneous pacing and/or isoprenaline 5 micrograms/min starting infusion or adrenaline 2-10 micrograms/min while arranging expert transvenous pacing.
  • Even after a satisfactory response, recent asystole, Mobitz II, complete block with broad QRS or a ventricular pause over 3 seconds signals risk of asystole.
  • Permanent pacing is driven by symptoms, block type, reversibility and rhythm; NICE recommends dual-chamber pacing for symptomatic SSS/AV block with specific exceptions.

Key red flags

Second-degree AV block

Mobitz I has progressive PR prolongation then a dropped QRS; Mobitz II has constant conducted PR intervals with unexpected dropped QRS. Mobitz II indicates RCUK asystole risk even after symptoms improve.

Complete AV block

P waves and QRS complexes are independent. A narrow junctional escape may be temporarily more reliable; a slow broad ventricular escape suggests infranodal disease and high risk.

Life-threatening features

Shock, syncope, myocardial ischaemia, severe heart failure or immediately post-ROSC. Extreme bradycardia may progress to effective cardiac arrest even before a pulse disappears.

Risk of asystole despite initial improvement

Recent asystole, Mobitz II AV block, complete heart block with broad QRS, or ventricular pause over 3 seconds.

Investigation priorities

01
ABCDE, repeated pulse/BP/perfusion assessment and continuous ECG/SpO2First step

Identify symptomatic low output and deterioration while treatment is prepared.

Management branches

No adverse featuresObserve, treat cause and assess asystole risk

Bradycardia without shock, syncope, ischaemia, severe heart failure or immediate post-ROSC state.

  1. Perform ABCDE, monitor, obtain 12-lead and identify reversible causes.
  2. If none of recent asystole, Mobitz II, complete block with broad QRS or pause over 3 seconds is present, observe and treat the cause.
  3. If an asystole-risk feature is present, seek urgent expert help, monitor in an appropriate area and consider transvenous pacing even if the current response appears satisfactory.
  4. Do not treat physiological asymptomatic sinus bradycardia purely to normalise the number.

Key medicines

Atropine IV500 micrograms IV; repeat every 3-5 minutes if needed to a maximum total of 3 mg.Do not give after cardiac transplant or in high-grade AV block with broad QRS per RCUK. It may be ineffective in distal block and should not delay pacing; monitor for tachyarrhythmia/ischaemia and anticholinergic effects.
Isoprenaline IV infusionRCUK starting rate 5 micrograms/min IV; titrate under continuous expert monitoring to perfusion and heart rate while pacing is arranged.Can provoke tachyarrhythmia and myocardial ischaemia and increase oxygen demand; continuous ECG/BP, correct hypovolaemia and avoid uncontrolled titration.
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Sources and review status6 sources · checked 25 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 25 Aug 2026; clinical approval remains outstanding.

  • RCUK 2025 Adult Advanced Life Support
  • RCUK Adult bradyarrhythmia algorithm 2025
  • NICE TA88: dual-chamber pacemakers for symptomatic bradycardia
  • NICE TA324: dual-chamber pacing in symptomatic sick-sinus syndrome without AV block
  • 2021 ESC cardiac pacing guideline landing pageDetailed diagnostic/pacing context where NICE technology appraisals are narrower.
  • RCUK ECG six-stage rhythm approach

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