2. Overview
Ventricular fibrillation (VF) is a common cause of sudden cardiac death
(SCD) and is sometimes preceded by monomorphic or polymorphic
ventricular tachycardia (VT). Although cardiopulmonary resuscitation,
including chest compressions and assisted ventilation, can provide
transient circulatory support for the patient with cardiac arrest, the only
effective approach for terminating VF is electrical defibrillation
Success with external defibrillation led to the development of an
implantable defibrillator, followed in 1980 by the first automatic internal
defibrillator implantation in humans . FDA approval followed in 1985,
initially only for secondary prevention in survivors of cardiac arrest.
3. Indications
Secondary prevention :
1- Patients with a prior episode of resuscitated VT/VF or sustained
hemodynamically unstable VT in whom a completely reversible cause cannot
be identified.
Includes :
- Those with idiopathic VT/VF and congenital long QT syndrome,
but not patients who have VT/VF limited to the first 48 hours after an
acute myocardial infarction (MI).
2- Patients with episodes of spontaneous sustained VT in the presence of
heart disease (valvular, ischemic, hypertrophic, dilated, or infiltrative
cardiomyopathies) and other settings (e.g., channelopathies).
4. Indications
Primary prevention
1- Patients with a prior MI (at least 40 days ago) and left ventricular ejection fraction (LVEF)
≤30 percent.
2- Patients with a cardiomyopathy, New York Heart Association (NYHA) functional class II to
III , and LVEF ≤35 percent.
3- Heart failure patients who have intraventricular conduction delay (≥120 milliseconds) .
4- High risk for life-threatening VT/VF includes :
- Patients with congenital long QT syndrome who have recurrent symptoms and/or
torsades de pointes despite therapy with beta blockers .
- High-risk patients with hypertrophic cardiomyopathy or arrhythmogenic right ventricular
ventricular (RV) cardiomyopathy.
- High-risk patients with Brugada syndrome, catecholaminergic polymorphic VT
5. Not Recommended
1. Patients with ventricular tachyarrhythmias due to a completely reversible
disorder in the absence of structural heart disease.
2. Patients who do not have a reasonable expectation of survival with an
acceptable functional status for at least one year.
3. Patients with incessant VT or VF in whom other therapies (e.g., catheter
ablation) should be considered first.
4. Patients with severe psychiatric illnesses that may be aggravated by
device implantation
6. Not Recommended
5. Patients with VF or VT amenable to surgical or catheter ablation in whom
the risk of sudden cardiac death is normalized after successful ablation.
6. Patients with syncope without inducible ventricular tachyarrhythmias and
without structural heart disease.
7. When To Consider
Patients with HF with reduced ejection fraction (HFrEF) with LV ejection
fraction (LVEF) ≤35 percent and it should be performed after patients have
received optimal (maximum tolerated up to target doses) evidence-based
medical therapy for at least three months after initial diagnosis of HFrEF
(or for at least 40 days after myocardial infarction) and after identification
and treatment of any reversible causes of LV systolic dysfunction .
Some patients with LVEF between 35 and 50 percent may be candidates
for CRT, including those anticipated to require frequent ventricular pacing
(generally >40 percent of the time) or who have a QRS ≥150 ms with left
bundle branch block (LBBB) and refractory symptoms attributable to HF.
8.
9.
10. Choice between CRT-D versus CRT-P
There are no prospective data demonstrating a survival benefit of CRT-D over
CRT-P .
In observational studies , Those less likely to benefit from CRT-D compared
with CRT-P include :
1- older patients (age ≥75 years)
2- patients without coronary artery disease particularly if they are without dilated
LV or midwall fibrosis
3- pacemaker-dependent patients without coronary artery disease.
CRT-P devices are smaller, less expensive, possibly incur less risk of infection, and
have been subject to fewer recalls and advisories .
11. ELEMENTS OF THE ICD
The ICD system is comprised of the following elements :
1. Pacing/sensing electrodes
2. Defibrillation electrodes
3. Pulse generator
