📋 Key Information Summary
- ICDs are life-saving devices that detect and terminate ventricular tachycardia (VT) and ventricular fibrillation (VF) using anti-tachycardia pacing (ATP) or defibrillation shocks.
- Primary prevention ICD: Implant in patients at high risk of sudden cardiac death (SCD) who have not experienced sustained VT/VF — requires LVEF ≤35% and NYHA II–III heart failure on optimal medical therapy ≥3 months, or specific cardiomyopathy/genetic criteria.
- Secondary prevention ICD: Implant in survivors of cardiac arrest due to VT/VF, or patients with sustained haemodynamically significant VT, or syncope with inducible VT — no LVEF threshold required.
- MADIT-II and SCD-HeFT trials demonstrated 23–31% relative mortality reduction with primary prevention ICDs in ischaemic and non-ischaemic cardiomyopathy.
- All ICD patients must be on guideline-directed medical therapy (GDMT) for at least 3 months before primary prevention implantation to allow LVEF reassessment.
- CRT-D (cardiac resynchronisation therapy–defibrillator) is preferred when LVEF ≤35% with QRS ≥150 ms and LBBB morphology.
- Subcutaneous ICD (S-ICD) avoids transvenous lead complications and is an option for patients without pacing indications.
- Inappropriate shocks occur in 10–20% of patients — SVT is the most common cause; correct programming and beta-blockers reduce risk.
- ICD infection is a serious complication with 18–40% in-hospital mortality for endocarditis; complete device and lead extraction is mandatory.
- Remote monitoring (e.g., Medtronic CareLink, Abbott Merlin) is standard of care and reduces time to clinical intervention.
- Regular device checks at 3–6 monthly intervals (in-clinic) with continuous remote monitoring between visits.
- Generator replacement depends on battery status (ERI); typical longevity is 5–7 years for single-chamber, 4–6 years for dual-chamber/CRT-D.
- End-of-life discussions should include ICD deactivation to avoid painful shocks in patients with irreversible terminal illness.
Introduction & Australian Epidemiology
Implantable cardioverter defibrillators (ICDs) deliver life-saving shock therapy for ventricular fibrillation (VF) and ventricular tachycardia (VT) and are indicated for both primary and secondary prevention of sudden cardiac death (SCD) in high-risk patients. Since the first human implant by Dr Michel Mirowski in 1980, ICDs have become the single most effective intervention for prevention of arrhythmic death.
In Australia, approximately 5,000–6,000 new ICDs are implanted annually, with over 40,000 patients currently living with an active device. Implantation is performed at tertiary cardiac centres across all states. The Australian Institute of Health and Welfare (AIHW) data indicate that cardiac arrhythmias contribute to approximately 25,000 deaths per year, with SCD accounting for an estimated 3,000–4,000 of these.
ICDs are classified as Class I (strong) indications by the Cardiac Society of Australia and New Zealand (CSANZ), European Society of Cardiology (ESC), and American Heart Association/American College of Cardiology (AHA/ACC) guidelines for both primary and secondary prevention in appropriate patient populations. Device therapy is funded under Medicare Benefits Schedule (MBS) item numbers for implantation, generator changes, and lead revisions.
Contemporary ICDs offer tiered therapy — starting with painless anti-tachycardia pacing (ATP) before escalating to high-energy defibrillation. Modern devices incorporate remote monitoring, MRI-conditional designs, and extended battery longevity. The shift towards subcutaneous ICD (S-ICD) systems further reduces transvenous lead-related complications.
Indications: Primary vs Secondary Prevention
Primary Prevention
Primary prevention ICDs are implanted in patients at high risk of SCD who have not yet experienced a life-threatening ventricular arrhythmia. Landmark randomised trials — MADIT (1996), MUSTT (1999), MADIT-II (2002), and SCD-HeFT (2005) — established mortality benefit in selected populations.
| Indication | Criteria | Class | Key Evidence |
|---|---|---|---|
| Ischaemic cardiomyopathy | LVEF ≤35%, NYHA II–III, ≥40 days post-MI, ≥3 months GDMT | Class I | MADIT-II, SCD-HeFT |
| Non-ischaemic dilated cardiomyopathy (DCM) | LVEF ≤35%, NYHA II–III, ≥3 months GDMT | Class I | SCD-HeFT, DANISH* |
| LVEF ≤30%, NYHA I (ischaemic) | ≥40 days post-MI, ≥90 days post-revascularisation | Class I | MADIT-II |
| Hypertrophic cardiomyopathy (HCM) | ≥1 major risk factor (see below) | Class IIa | ESC HCM Guidelines 2020 |
| Arrhythmogenic right ventricular cardiomyopathy | ≥1 risk factor for SCD | Class IIa | Padua criteria |
| Long QT syndrome | Syncope/beta-blocker failure, QTc ≥500 ms | Class IIa | AHA/ACC 2017 |
| Brugada syndrome | Survived cardiac arrest, spontaneous VT with syncope | Class I (secondary prev.) | Brugada Consensus 2013 |
DANISH Trial note: The DANISH trial (2016) showed no significant all-cause mortality benefit for ICD in non-ischaemic DCM, though SCD was reduced by 50%. CSANZ and ESC still recommend primary prevention ICD in non-ischaemic DCM with LVEF ≤35% and NYHA II–III, but shared decision-making is emphasised.
HCM Major Risk Factors for SCD
- Maximum left ventricular wall thickness ≥30 mm
- Family history of SCD in first-degree relative <40 years
- Unexplained syncope within preceding 6 months
- Non-sustained VT on Holter (≥3 beats at ≥120 bpm)
- Abnormal exercise blood pressure response (hypotensive or blunted rise)
- Late gadolinium enhancement on CMR (extensive fibrosis ≥15% LV mass)
Secondary Prevention
Secondary prevention ICDs are implanted in patients who have survived a cardiac arrest or experienced sustained VT. The AVID (1997), CIDS (2000), and CASH (2000) trials demonstrated 20–31% relative reduction in mortality compared with amiodarone.
| Indication | Class | Notes |
|---|---|---|
| Survived cardiac arrest (VF/VT) not due to reversible cause | Class I | Exclude acute MI <48 h, correctable electrolyte/ischaemic cause |
| Sustained VT with haemodynamic compromise | Class I | Regardless of LVEF |
| Syncope with inducible VT on EPS | Class I | EPS indicated when cause of syncope unclear |
| Sustained VT with near-normal LVEF | Class I | Consider underlying channelopathy or structural disease |
Reversible causes: ICD implantation is NOT indicated for VT/VF occurring within 48 hours of acute myocardial infarction, or due to fully correctable causes (e.g., severe electrolyte disturbance, drug toxicity, myocarditis with full recovery). These patients should undergo reassessment at 3 months.
Device Components & Programming
System Components
Transvenous ICD System
Medtronic Evera™ · Abbott Gallant™ · Boston Scientific Dynagen™
Generator
Subpectoral or pre-pectoral can; single-, dual-chamber, or CRT-D
Defibrillation lead
Right ventricular (RV) apex or septum; integrated bipolar/sensing
Pacing leads
Atrial lead (dual-chamber), LV lead via coronary sinus (CRT-D)
MRI conditional
Most current models are 1.5 T and 3 T conditional
Subcutaneous ICD (S-ICD)
Boston Scientific EMBLEM™ MRI S-ICD
Generator
Left lateral thorax (subcutaneous)
Lead
Subcutaneous electrode along left parasternal line
Advantages
No transvenous lead — eliminates lead fracture, venous occlusion, endocarditis risk
Limitations
No bradycardia or ATP pacing; larger shocks; size/weight limit
Indication
Patients without need for pacing, CRT, or ATP; young patients; venous access issues
ICD Programming — Rate Zones & Therapies
Modern ICDs use programmable rate-based detection zones and tiered therapy. Evidence from the ADVANCE III, MADIT-RIT, and PROVIDE trials demonstrates that long detection intervals and high rate thresholds significantly reduce inappropriate shocks.
| Zone | Rate Threshold | Detection | Therapy |
|---|---|---|---|
| VT-1 (slow VT) | 150–188 bpm | 30/40 intervals | ATP (burst, 8 pulses, 88% CL), then shock |
| VT-2 (fast VT) | 188–250 bpm | 18/24 intervals | ATP (burst), then shock 36 J → 36 J → 36 J |
| VF | >250 bpm | 12/16 intervals | Shock 36 J → 36 J → 36 J (max energy) |
Programming principle: "Higher, slower, longer" — higher rate cutoffs, slower detection (long detection intervals), and ATP before shock reduces inappropriate and unnecessary therapies without increasing mortality (MADIT-RIT, ADVANCE III).
Anti-Tachycardia Pacing (ATP)
ATP is a painless pacing therapy that terminates monomorphic VT by penetrating and resetting the re-entrant circuit. Up to 70–80% of VTs ≤200 bpm are terminated by ATP alone, avoiding painful shocks. ATP programming should include burst pacing at 84–88% of the VT cycle length.
Complications
Inappropriate Shocks
Inappropriate shocks are delivered for rhythms other than VT/VF, occurring in 10–20% of patients over 3–5 years. They cause significant psychological distress, reduce quality of life, and are associated with increased mortality.
Common Causes
SVT/AF with Rapid Ventricular Response
Accounts for 50–60% of inappropriate shocks. Rate exceeds VT detection zone.
Prevention: rate discrimination algorithms (onset, stability, morphology); optimise rate control with beta-blockers
Moderate Causes
T-wave Oversensing / Myopotentials
R-wave double counting or skeletal muscle noise sensed as VF. More common with integrated bipolar leads.
Prevention: adjust sensitivity; change lead polarity to true bipolar; reposition lead if recurrent
Serious Causes
Lead Fracture / Connector Problem
High-voltage noise artefact triggers VF zone. Medical emergency — requires urgent revision.
Prevention: epicardial or S-ICD in young/active patients; system revision for recurrent fracture
Recurrent inappropriate shocks: Patients presenting with ≥2 inappropriate shocks should have urgent device interrogation. If lead fracture or system malfunction is identified, the affected zone should be deactivated and revision scheduled promptly. Repeat shocks cause myocardial injury and worsen outcomes.
ICD Infection
Pocket infection and CIED (cardiac implantable electronic device) endocarditis occur in 0.5–2.2% of initial implants and 1–4% of revision procedures. Staphylococcus aureus and coagulase-negative staphylococci (CoNS) account for >70% of cases.
1
Pocket Infection
Erythema, warmth, erosion, purulent discharge at generator site. Usually within 12 months of procedure. Blood cultures may be negative.
2
CIED Endocarditis
Lead vegetations on echocardiography (TOE superior to TTE), positive blood cultures, systemic sepsis. Higher mortality (18–40% in-hospital).
3
Management
Complete device and lead extraction is mandatory for all CIED infections. IV antibiotics ≥2–4 weeks post-extraction (6 weeks if endocarditis). Re-implant at contralateral site after blood culture clearance.
Antibiotic Therapy for CIED Infection
Flucloxacillin
Staphylex® · Generic · Penicillinase-resistant penicillin
Adult dose
2 g IV 4–6 hourly (12 g/day)
Duration
4 weeks (pocket infection) to 6 weeks (endocarditis)
Renal adjustment
No dose adjustment required; monitor in severe CKD
PBS status
✔ PBS General Benefit
Vancomycin
Generic · Glycopeptide (MRSA cover)
Adult dose
15–20 mg/kg IV 12 hourly (target trough 15–20 mg/L)
Indication
MRSA/MRSE or penicillin allergy
Renal adjustment
Dose and interval adjustment required; therapeutic drug monitoring essential
PBS status
✔ PBS General Benefit
Ceftriaxone
Rocephin® · Generic · Third-generation cephalosporin
Adult dose
2 g IV once daily
Indication
Gram-negative organisms, HACEK organisms
Renal adjustment
No dose adjustment required
PBS status
✔ PBS General Benefit
Other Complications
| Complication | Incidence | Management |
|---|---|---|
| Pneumothorax | 0.5–2% | Aspiration or chest drain if symptomatic |
| Lead dislodgement | 1–2% | Repositioning within 6 weeks |
| Cardiac perforation/tamponade | 0.1–0.5% | Emergent pericardiocentesis; surgical repair |
| Venous thrombosis/occlusion | 2–5% | Anticoagulation; contralateral re-implant if severe |
| Lead fracture | 1–3% at 5 years | Lead revision or extraction |
| Twiddler syndrome | <1% | Generator pocket revision; suture anchoring |
| Electrical storm (≥3 shocks in 24 h) | 10–30% (lifetime) | IV amiodarone, sedation, beta-blockade, catheter ablation |
Device Checks & Follow-Up
Follow-Up Schedule
Post-ICD implantation follow-up is essential for safety, battery monitoring, arrhythmia review, and optimisation of device programming. Remote monitoring is now standard of care and is endorsed by CSANZ, ESC, and HRS/EHRS.
24–72 hours
Post-implant wound check, chest X-ray, threshold testing. Verify sensing, pacing, and defibrillation safety margin (≥10 J below maximum output).
2–6 weeks
First in-clinic device check. Assess wound healing, lead impedances, thresholds, arrhythmia history. Enrol in remote monitoring programme.
3 months
Review GDMT optimisation; assess for shock burden, SVT episodes, lead parameters. Programme any necessary zone or therapy adjustments.
6–12 monthly
Routine in-clinic reviews. Battery status (ERI check), lead integrity, arrhythmia log review, programming adjustments as needed.
ERI (Elective Replacement Indicator)
Generator replacement within 3 months of ERI notification. Safety period after ERI is approximately 3 months depending on manufacturer.
Remote Monitoring
Remote Monitoring Platforms
Medtronic CareLink™ · Abbott MyMerlin™ · Boston Scientific LATITUDE™
Function
Daily automatic transmission of device status, arrhythmia events, lead parameters
Alert transmission
Immediate notification for VT/VF therapies, lead alerts, battery ERI
Evidence
CONNECT, TRUST trials: reduced time to clinical decision; reduced ED visits
MBS coverage
Device check items apply; remote monitoring itself is manufacturer-funded
At Each Device Check — Essential Components
1
Interrogation
Download arrhythmia log, shock/ATP therapies, percentage pacing, battery longevity, lead impedances and thresholds.
2
Clinical Review
Symptom assessment, syncope/presyncope, palpitations, exercise tolerance. Review medications (drug interactions with amiodarone, QT-prolonging agents).
3
Programming
Adjust rate zones, detection intervals, ATP/shock therapies based on arrhythmia burden. Review SVT discrimination settings.
4
Safety Checks
Defibrillation threshold testing if lead revision or new implant. Assess for lead advisories (manufacturer recalls). Check MRI conditional status before any imaging.
MRI safety: Most current ICDs are MRI-conditional (1.5 T and/or 3 T). Before any MRI, confirm the device model is MRI-compatible, programme the device to "MRI mode," and ensure continuous monitoring during scanning. Post-scan, restore normal programming immediately. Non-MRI conditional devices are an absolute contraindication to MRI.
Special Populations
Pregnancy
ICD in Pregnancy
ICDs can be implanted in the second trimester under echocardiographic guidance (no fluoroscopy). Subcutaneous ICD preferred to avoid radiation. Transvenous ICD can be performed with minimal fluoroscopy and lead shielding. Pregnant patients with existing ICDs should be monitored for lead integrity as cardiac remodelling may alter thresholds.
Paediatrics
Paediatric ICD Considerations
Channelopathies (LQTS, CPVT, Brugada) and HCM are common indications. Epicardial leads preferred in small children (<30 kg). S-ICD may be unsuitable in paediatric patients due to body habitus. Higher rate of lead revisions due to growth. Psychological support essential — shocks can cause PTSD in children and adolescents.
Elderly (≥75 years)
Geriatric Considerations
Mortality benefit of primary prevention ICD attenuates after age 75–80. Shared decision-making regarding comorbidity burden, frailty, and goals of care. Danicic et al. and NICE guidelines suggest careful patient selection. Consider S-ICD to avoid transvenous complications. Life expectancy <1 year is a relative contraindication.
Renal Impairment
CKD and Dialysis Patients
ICD infection risk is significantly higher in dialysis patients (up to 10×). Defibrillation thresholds may be higher. CRT-D often preferred as CKD is frequently associated with cardiomyopathy. Vancomycin dosing requires TDM in CKD. Ensure dialysis access planning does not compromise ipsilateral ICD implantation.
Immunocompromised
Immunosuppressed Patients
Higher infection risk with device implantation. Consider perioperative antibiotics beyond standard prophylaxis. Subcutaneous ICD may be preferred to avoid transvenous infection risk. Close follow-up for pocket healing. SOT and chemotherapy patients — coagulation status must be optimised prior to implant.
End-of-Life & ICD Deactivation
ICD deactivation is an essential component of advance care planning for patients with terminal illness. Delivering shocks to dying patients causes suffering without altering outcomes. ICD deactivation should be discussed as part of palliative care planning, ideally well before end-stage disease.
Ethical obligation: All Australian healthcare professionals have an obligation to discuss ICD deactivation in patients with irreversible terminal illness. Deactivation of the shock function does NOT deactivate bradycardia pacing, which may continue to be appropriate. A magnet can temporarily suspend tachyarrhythmia therapies in an emergency.
Process: Device deactivation requires device interrogation by a cardiac physiologist, EP nurse, or cardiologist. The defibrillation function is programmed off while bradycardia pacing may be maintained if clinically appropriate. Written documentation of deactivation should be added to the patient's advance care directive.
Aboriginal and Torres Strait Islander Health Considerations
Aboriginal and Torres Strait Islander Health
📚 References
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