Indications for Implantable Cardioverter-Defibrillator (ICD) Therapy
An Implantable Cardioverter-Defibrillator (ICD) is used to prevent sudden cardiac death by treating life-threatening ventricular arrhythmias such as ventricular tachycardia (VT) and ventricular fibrillation (VF).
ICDs may also provide backup pacing, anti-tachycardia pacing (ATP), and cardioversion/defibrillation shocks.
The American College of Cardiology (ACC), American Heart Association (AHA), and Heart Rhythm Society (HRS) publish guideline-based recommendations for ICD implantation.
Primary Reference:
2017 ACC/AHA/HRS Guideline for Management of Ventricular Arrhythmias and Prevention of Sudden Cardiac Death
Purpose of an ICD
ICDs are used for:
Prevention of sudden cardiac death (SCD)
Treatment of sustained VT/VF
Protection in patients with reduced ejection fraction
Arrhythmia termination through ATP or shock therapy
Indications fall into two broad categories:
I. Secondary Prevention ICD Indications
ICD implantation is Class I (definite) for patients who have survived:
Cardiac arrest due to VF not from a reversible cause
Sustained VT with hemodynamic compromise
Spontaneous sustained VT, even if hemodynamically stable
VT/VF occurring >48 hours after MI (and not due to transient ischemia)
These patients have a high risk of recurrent life-threatening arrhythmias.
II. Primary Prevention ICD Indications
Primary prevention aims to stop sudden cardiac death before the first arrhythmic event.
A. Ischemic Cardiomyopathy
Class I (recommended):
Left ventricular ejection fraction (LVEF ≤ 35%)
At least 40 days post-MI
On optimal guideline-directed medical therapy
NYHA Class II or III symptoms
Class I (recommended):
B. Non-Ischemic Cardiomyopathy
C. Genetic and Structural Heart Diseases
Class I (recommended):
Hypertrophic cardiomyopathy with high-risk features (e.g., massive LVH, syncope, NSVT, family history of SCD)
Arrhythmogenic right ventricular cardiomyopathy (ARVC) with sustained VT or severe dysfunction
Long QT syndrome with syncope or documented VT/VF
Brugada syndrome with syncope or documented arrhythmia
Catecholaminergic polymorphic VT (CPVT) with stress-induced syncope or VT
Reference:
ESC Guidelines – Sudden Cardiac Death
III. ICD After Cardiac Procedures or Acute Events
ICD may be indicated after:
Cardiac surgery if persistent VT/VF
Revascularization only after waiting period, unless VT/VF persists
Myocarditis, sarcoidosis, or infiltrative disease with malignant arrhythmias
ICD is not indicated if the arrhythmia is due to:
IV. Contraindications (Class III – NOT Indicated)
ICD implantation is not appropriate when:
Ventricular arrhythmia is due to a reversible cause
Patient has LVEF > 35% without other risk factors
Expected survival is < 1 year due to non-cardiac disease
NYHA Class IV heart failure not eligible for transplant or LVAD
Patient declines device therapy
V. Summary Table: ICD Indications
| Condition | Indication | Class |
| VF arrest not from reversible cause | ICD recommended | Class I |
| Sustained VT with hemodynamic compromise | ICD recommended | Class I |
| Spontaneous sustained VT (stable or unstable) | ICD recommended | Class I |
| Post-MI LVEF ≤35% (NYHA II–III, ≥40 days post-MI) | ICD recommended | Class I |
| Post-MI LVEF ≤30% (NYHA I, ≥40 days post-MI) | ICD recommended | Class I |
| Non-ischemic cardiomyopathy LVEF ≤35% (NYHA II–III) | ICD recommended | Class I |
| Hypertrophic cardiomyopathy w/ high-risk features | ICD recommended | Class I |
| Long QT syndrome with syncope/VT | ICD recommended | Class I |
| Brugada syndrome with syncope/VT | ICD recommended | Class I |
| ARVC with sustained VT or severe dysfunction | ICD recommended | Class I |
| Reversible arrhythmias (drugs, electrolytes) | ICD not indicated | Class III |
| Severe comorbid illness with life expectancy <1 yr | ICD not indicated | Class III |
Key Takeaways
ICDs prevent sudden cardiac death by treating VT/VF.
Secondary prevention ICDs are used after life-threatening arrhythmias.
Primary prevention ICDs are used in patients with low EF or high-risk inherited conditions.
ICD is not indicated if the arrhythmia is due to a correctable or transient cause.
Decisions should follow ACC/AHA/HRS guideline recommendations.