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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.

Implantable cardioverter-defibrillators and CRT

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

RapidFull
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Escalate

Call 999 after more than one ICD shock, any shock with collapse or ongoing chest pain, breathlessness, palpitations or presyncope, or suspected electrical storm. If a shockable cardiac arrest persists, deliver external defibrillation with pads more than 8 cm from the generator; a magnet can suspend inappropriate ICD shocks but does not disable pacing.

Synopsis

Select ICD or cardiac resynchronisation therapy for appropriate arrhythmic and heart-failure indications, and respond safely to shocks and device complications.

  • An ICD detects ventricular tachyarrhythmia and can deliver anti-tachycardia pacing or a shock; it does not prevent the arrhythmia from starting.
  • Secondary prevention considers survivors of VT/VF arrest or haemodynamically important sustained VT after reversible causes are excluded.
  • Primary prevention balances LVEF, heart-failure status, substrate, life expectancy and competing non-arrhythmic mortality after optimised treatment.
  • CRT coordinates ventricular contraction using biventricular or conduction-system pacing; CRT-P paces, while CRT-D also defibrillates.
  • NICE TA314 uses LVEF 35% or less plus NYHA class, QRS duration and LBBB morphology to select ICD, CRT-P or CRT-D.
  • The strongest conventional CRT response is expected with symptomatic HFrEF, sinus rhythm, LBBB and QRS 150 ms or more despite optimised therapy.
  • One shock with complete recovery still requires prompt device-team contact; repeated shocks or ongoing symptoms are an emergency.
  • Inappropriate shocks can result from AF/SVT, lead noise or programming; interrogation of stored electrograms is essential.

Key red flags

Electrical storm

Three or more episodes of sustained ventricular arrhythmia or appropriate ICD therapies within 24 hours is a critical syndrome requiring specialist intensive management.

Device infection or lead complication

Pocket inflammation, erosion, fever, bacteraemia, diaphragmatic stimulation, syncope or abrupt lead-parameter change requires prompt device assessment.

Investigation priorities

01
Device interrogation with stored electrogramsFirst step

Determine rhythm, therapy sequence, appropriateness, battery and lead integrity.

Management branches

secondarySecondary-prevention ICD assessment

The patient survives VT/VF arrest or sustained haemodynamically important VT.

  1. Stabilise, document the rhythm and identify reversible causes such as acute ischaemia, electrolyte disturbance, drug toxicity or a transient acute illness.
  2. Assess ventricular function, coronary disease, cardiomyopathy, neurological outcome, comorbidity and expected meaningful survival.
  3. If no fully reversible cause explains the event and recurrent malignant ventricular arrhythmia risk remains, refer for specialist ICD evaluation.
  4. Discuss transvenous versus subcutaneous/extravascular systems, pacing need, shocks, complications, driving and future shock deactivation.
Open full textbook →Answer 2 questionsCardiology check
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. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE TA314: ICDs and cardiac resynchronisation therapyUK selection matrix and ICD/CRT recommendations.
  • NICE NG106: Chronic heart failureOptimised HFrEF management and referral context.
  • ESC: 2021 cardiac pacing and CRT guidelineCRT phenotype and AF capture strategy.
  • ESC: 2022 ventricular arrhythmias guidelineICD prevention and ventricular-arrhythmia assessment.
  • Resuscitation Council UK: Adult advanced life support 2025External defibrillation and magnet actions in ICD patients.
  • NHS: Pacemaker and ICD patientsCurrent shock safety advice and escalation.

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