From the Guidelines
Implantable cardioverter-defibrillators (ICDs) are recommended for survivors of cardiac arrest due to ventricular tachycardia (VT) or ventricular fibrillation (VF) when there is no completely reversible cause identified, as they have been shown to reduce sudden death and total mortality compared to antiarrhythmic drug therapy 1. The primary indication for ICDs is for secondary prevention of sudden cardiac death in patients who have already experienced a life-threatening arrhythmia.
Key Indications
- Cardiac arrest survivors with structural heart disease
- Those with a left ventricular ejection fraction (LVEF) ≤35%
- Patients with inherited arrhythmia syndromes like Long QT syndrome, Brugada syndrome, or hypertrophic cardiomyopathy who have survived a cardiac arrest ICDs are not indicated when the cardiac arrest was due to a completely reversible cause such as acute myocardial infarction, electrolyte abnormalities, drug overdose, or other transient factors that have been fully corrected.
Timing of ICD Implantation
The timing of ICD implantation is typically at least 40 days after myocardial infarction and 90 days after revascularization, as earlier implantation has not shown mortality benefit.
Mechanism of Action
ICDs work by continuously monitoring heart rhythm and delivering electric shocks when dangerous arrhythmias are detected, thereby terminating the arrhythmia and preventing sudden death.
Additional Features
Modern devices also provide anti-tachycardia pacing, bradycardia pacing support, and can store data about arrhythmic events for physician review, as supported by guidelines from the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society 1.
From the Research
Indications for ICD after Cardiac Arrest
The indications for implantable cardioverter-defibrillator (ICD) therapy after cardiac arrest are based on various studies, including:
- Survivors of sudden cardiac arrest (SCA) with a reversible cause, except in those with completely reversible causes 2
- Patients with sustained ventricular tachycardia (VT) and aborted sudden cardiac death (SCD), where ICD therapy has been shown to significantly increase survival 3
- Survivors of out-of-hospital cardiac arrest due to ventricular fibrillation (OHCA-VF), where the subcutaneous implantable defibrillator (S-ICD) may be a suitable option for those without a remote myocardial infarction and left ventricular ejection fraction (LVEF) > 35% 4
Patient Selection for ICD Therapy
Patient selection for ICD therapy after cardiac arrest depends on various factors, including:
- Presence of a reversible cause of SCA 2
- History of myocardial infarction (MI) and LVEF 3, 4
- Presence of non-sustained VT and decreased LVEF 3
- Age, sex, and comorbidity burden, which are not associated with ICD implantation 5
- STEMI and successful revascularization, which are inversely associated with ICD implantation 5
Outcomes of ICD Therapy
The outcomes of ICD therapy after cardiac arrest include:
- Lower all-cause mortality in survivors of SCA with a reversible cause, except in those with myocardial infarction 2
- Improved survival in patients with sustained VT and aborted SCD 3
- Reduced mortality in survivors of OHCA-VF with early ICD implantation, after adjustment for prognostic factors 5
- Appropriate ICD shock therapy in 15% of patients with early ICD implantation 5