CardiologyTier 2Topic

Defibrillators (know indications for)

What an ICD does

ICD terminates VT/VF by anti-tachycardia pacing or shock
Prolongs life; does not treat heart failure and does not improve symptoms
- CRT improves symptoms - the two are often combined (CRT-D)

Device	Use	Limitation
Transvenous ICD	Standard	Lead complications, infection, extraction risk
Subcutaneous ICD	HCM, long QT, young patients, poor venous access, prior device infection	No bradycardia pacing, no anti-tachycardia pacing, no CRT
Wearable defibrillator	Bridging a temporary high-risk period	Adherence-dependent

Use in Australia

Most implants are for ischaemic cardiomyopathy
Uptake in Australia limited by access, referral patterns and remoteness
Appropriate shock rates are much lower than trial-era estimates - modern medical therapy has reduced arrhythmic death

Substrate for sudden cardiac death

Substrate for sudden cardiac death:
- Scar (post-MI) or fibrosis (cardiomyopathy)
- -> zones of slow conduction
- -> reentrant VT
- -> degeneration to VF
Channelopathies produce SCD without structural disease - repolarisation or depolarisation abnormality
An ICD treats the arrhythmia, not the substrate - optimal medical therapy still comes first

Assessment before implant

EF on echo - after >=3 months of optimal medical therapy, and >=40 days post-MI
Reversible causes excluded - ischaemia, electrolytes, drugs, thyroid
Life expectancy and functional status
Holter/loop recorder for NSVT
CMR for scar burden where the aetiology is unclear
Genetic testing and family screening in inherited arrhythmia syndromes

Secondary prevention - implant if

Survived VT/VF cardiac arrest from a non-reversible cause, OR
Haemodynamically significant sustained VT, OR
Sustained VT with LV dysfunction
"Reversible" means genuinely reversible - acute ischaemia treated by revascularisation, not simply "the potassium was low"

Primary prevention - implant if all of

Primary prevention - implant if all of

LVEF <=35%, AND
NYHA II-III, AND
>=3 months optimal medical therapy, and >=40 days post-MI, AND
Expected meaningful survival >1 year

Primary prevention in high-SCD-risk conditions

Primary prevention in high-SCD-risk conditions

Hypertrophic cardiomyopathy
Long QT syndrome
Brugada syndrome
Arrhythmogenic right ventricular cardiomyopathy
Selected repaired congenital heart disease (e.g. TOF with QRS >180 ms)

Caveats

DANISH: no significant mortality benefit in non-ischaemic cardiomyopathy, especially over 60 - guidelines still recommend it, but the discussion is genuinely balanced
Do not implant if NYHA IV without CRT or transplant candidacy

Ongoing care

Device checks, remote monitoring
Deactivation discussion as part of advance care planning - raise it before the terminal phase
Driving restrictions after implant and after any shock

Who gets them

Ischaemic cardiomyopathy - the largest group
Dilated cardiomyopathy
HCM, ARVC
Channelopathies - long QT, Brugada, CPVT
Repaired congenital heart disease
Cardiac sarcoidosis and amyloidosis

Complications

Inappropriate shocks - AF with rapid ventricular response, SVT, lead noise, T-wave oversensing
- Psychologically damaging and associated with worse outcomes
Lead failure and fracture
Device infection - often requires complete system extraction
Pneumothorax, haematoma, tricuspid regurgitation

Monitor

Shock burden and appropriateness
Battery and lead integrity
EF - a recovered EF does not automatically mean the device is removed
End-of-life deactivation planning

11 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.

Get premium access