01Purpose and principlesWhat the treatment does and how it fits into care.
ICD and CRT solve different problems. An ICD terminates dangerous ventricular rhythms; CRT treats electromechanical dyssynchrony and can improve symptoms and outcomes in selected HFrEF. A combined CRT-D is chosen when both benefits are expected.
Device eligibility is not based on LVEF alone. Clinicians confirm optimised medical therapy, QRS morphology and duration, functional class, arrhythmic history, reversible causes, comorbidity, patient goals and a reasonable prospect of meaningful survival.
Long-term care includes programming, remote monitoring, heart-failure optimisation, psychological support and advance-care planning. Deactivating ICD shock therapy near end of life does not ordinarily turn off pacing.
Key points
- 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.
02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.
Stored electrograms show sustained VT or VF meeting programmed criteria, treated by anti-tachycardia pacing or shock.
Rapid AF/SVT, over-sensing, lead fracture or electromagnetic noise can trigger therapy without ventricular tachyarrhythmia.
Three or more episodes of sustained ventricular arrhythmia or appropriate ICD therapies within 24 hours is a critical syndrome requiring specialist intensive management.
Persistent symptomatic HFrEF with LVEF 35% or less and a broad QRS, especially LBBB at 150 ms or more, after optimised therapy is the classic profile.
Persistent symptoms may reflect inadequate biventricular pacing, AF, suboptimal lead position, scar, untreated ischaemia/valve disease or insufficient medical optimisation.
Pocket inflammation, erosion, fever, bacteraemia, diaphragmatic stimulation, syncope or abrupt lead-parameter change requires prompt device assessment.
03Assessment before treatmentTests and checks that guide safe selection.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Device interrogation with stored electrogramsFirst step - Why
- Determine rhythm, therapy sequence, appropriateness, battery and lead integrity.
- Interpretation and limitations
- Do not label a shock appropriate from symptoms alone; stored ventricular and atrial signals adjudicate mechanism.
- 02
12-lead ECG - Why
- Assess rhythm, QRS duration/morphology, pacing capture and post-shock changes.
- Interpretation and limitations
- Measure QRS before CRT selection; after CRT, morphology and pacing markers help confirm biventricular activation.
- 03
Echocardiogram - Why
- Measure LVEF, chamber size, valve disease and response to CRT.
- Interpretation and limitations
- Eligibility commonly uses LVEF 35% or less; repeat after optimised treatment and after CRT to assess reverse remodelling.
- 04
U&Es, magnesium and troponin when indicated - Why
- Find triggers for VT/VF and assess consequences of repeated therapy.
- Interpretation and limitations
- Correct electrolytes; interpret troponin with symptoms, shocks and ischaemic context.
- 05
Coronary and structural assessment - Why
- Identify reversible ischaemia, scar, cardiomyopathy or valve disease.
- Interpretation and limitations
- Revascularisation or disease-specific treatment may be needed alongside, before or instead of device therapy.
- 06
Chest radiograph and blood cultures when indicated - Why
- Assess lead position, pneumothorax or suspected infection.
- Interpretation and limitations
- Positive cultures or pocket erosion can mandate complete system extraction; a normal radiograph does not exclude electrical lead failure.
04Treatment approachPreparation, options, escalation and aftercare.
01secondarySecondary-prevention ICD assessmentFirst stepThe patient survives VT/VF arrest or sustained haemodynamically important VT.+
- 1Stabilise, document the rhythm and identify reversible causes such as acute ischaemia, electrolyte disturbance, drug toxicity or a transient acute illness.
- 2Assess ventricular function, coronary disease, cardiomyopathy, neurological outcome, comorbidity and expected meaningful survival.
- 3If no fully reversible cause explains the event and recurrent malignant ventricular arrhythmia risk remains, refer for specialist ICD evaluation.
- 4Discuss transvenous versus subcutaneous/extravascular systems, pacing need, shocks, complications, driving and future shock deactivation.
02hf-selectionPrimary prevention and CRT selectionHFrEF persists despite optimised evidence-based treatment.+
- 1Confirm LVEF, NYHA class, sinus rhythm/AF, QRS duration and LBBB morphology after treatment optimisation.
- 2Use the NICE TA314 matrix for LVEF 35% or less: narrow QRS generally favours ICD only when sudden-death risk is high; broader QRS and LBBB increasingly favour CRT-P or CRT-D according to NYHA class and defibrillator indication.
- 3For the classic LBBB QRS 150 ms or more phenotype, recommend CRT when symptoms and prognosis support it; choose CRT-D when defibrillation benefit is also expected and CRT-P when it is not.
- 4In AF, ensure a plan for high biventricular capture; ESC advises considering AV-junction ablation if conducted AF prevents more than 90-95% capture.
03shockAfter an ICD shockThe patient reports device therapy.+
- 1If more than one shock, collapse or ongoing chest pain, breathlessness, palpitations or presyncope occurs, call 999 and use monitored emergency care.
- 2If a single shock occurs and the patient feels completely well, contact the device service promptly the same day or as instructed and transmit a remote interrogation; do not drive until advised.
- 3Interrogate stored electrograms, check electrolytes/ischaemia and distinguish appropriate VT/VF therapy from inappropriate sensing or SVT.
- 4Treat the trigger, optimise programming and medicines, and consider VT ablation for recurrent appropriate therapy rather than accepting repeated shocks.
04active-shocksCardiac arrest or inappropriate repeated shocksThe ICD is repeatedly discharging or cardiac arrest persists.+
- 1AlternativeFor cardiac arrest, start ALS and give external shocks when indicated, placing pads more than 8 cm from the generator or using an alternative position.
- 2If shocks are clearly inappropriate and a perfusing rhythm persists, place a clinical magnet over the ICD to suspend tachy-therapies while monitoring continuously and obtaining immediate device help.
- 3Remember the magnet ordinarily does not disable bradycardia pacing; remove it if malignant ventricular arrhythmia develops and external defibrillation is not immediately ready.
- 4After stabilisation, interrogate and correct programming, lead or rhythm causes before discharge.
05Complications, monitoring and follow-upAdverse effects, response and longer-term review.
- Use scheduled and remote interrogation for battery, lead impedance, sensing, capture, arrhythmia episodes and delivered therapies.
- Track heart-failure symptoms, weight, renal function, blood pressure and adherence to evidence-based HFrEF therapy.
- After CRT, measure biventricular pacing percentage and reassess ECG and LVEF; investigate capture below the desired near-continuous range.
- Review every shock using stored electrograms and address psychological distress as well as the arrhythmic cause.
- Inspect the pocket and act on fever, erosion, redness, swelling or discharge.
- Revisit goals of care and shock-deactivation preferences during progressive illness; document that pacing can remain active when shock therapy is withdrawn.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
ICD treats, it does not prevent
Anti-tachycardia pacing and shocks terminate detected rhythms. Treating ischaemia, heart failure and arrhythmic substrate reduces recurrence and shock burden.
CRT needs capture
AF with rapid conducted beats can prevent effective biventricular pacing; rate control or AV-junction ablation may be required to deliver the intended therapy.
A magnet is temporary
Over an ICD it usually suspends tachycardia detection/therapy only while present. It is a bridge to expert correction, not definitive treatment.
External shocks remain valid
An ICD does not preclude standard ALS defibrillation; move pads away from the generator to reduce device damage and current shunting.
CRT-P versus CRT-D is a prognosis decision
Adding defibrillation makes sense only when arrhythmic death risk and meaningful survival justify shocks beyond the resynchronisation benefit.
Shock deactivation is not euthanasia
Stopping burdensome tachy-therapies allows the underlying disease to take its course and can be separated from ongoing bradycardia pacing.
07Common pitfallsFrequent interpretation and management errors.
- 01
Assuming every ICD shock is appropriate without stored-electrogram review.
- 02
Leaving a patient at home after repeated shocks or a shock with ongoing symptoms.
- 03
Applying external pads directly over the device generator.
- 04
Choosing CRT from LVEF alone without QRS duration, morphology, NYHA class and optimised treatment.
- 05
Assuming ICD shock deactivation also stops pacing.