ICD Indications
Secondary Prevention (Strongest Indications)
ICD implantation is mandatory for all patients resuscitated from cardiac arrest due to VT/VF or those with sustained VT causing hemodynamic compromise, as this represents the highest level of evidence for mortality benefit. 1
Core Secondary Prevention Criteria
Cardiac arrest survivors with documented VT/VF require ICD implantation regardless of underlying cardiac pathology, representing a Class I indication with Level A evidence 2, 1
Hemodynamically significant sustained VT warrants ICD placement even without prior cardiac arrest, based on proven survival benefit in the AVID trial 2, 1
Structural heart disease with spontaneous sustained VT (stable or unstable) mandates ICD therapy 2
Critical Exception to Secondary Prevention
- Do NOT implant an ICD if the cardiac arrest occurred during acute MI with normal LV function and complete revascularization was achieved, as the arrhythmogenic substrate was transient 1
Post-Revascularization Secondary Prevention
Patients with prior VT/VF and abnormal LV function should receive ICDs regardless of revascularization timing, as the arrhythmogenic substrate persists despite coronary intervention. 2, 1
If LV function is abnormal (LVEF reduced) and cardiac arrest was likely ischemia-related but revascularization performed: ICD is recommended 2
If LV function is normal and arrest was ischemia-related with successful revascularization: ICD can be useful 2
If arrest was unrelated to ischemia/injury: ICD is recommended regardless of LV function 2, 1
Within 90 days of revascularization with sustained VT not clearly related to acute MI/ischemia: ICD is recommended 2
Common Pitfall
Do not withhold ICD from post-revascularization patients based solely on improved LVEF—the AVID Registry showed similar or worse mortality in "correctable cause" patients treated with revascularization alone 2, 1
Primary Prevention Indications
Ischemic Cardiomyopathy
LVEF ≤30% with prior MI (>40 days post-MI): ICD recommended based on MADIT-II criteria 3
LVEF ≤35% with NYHA Class II-III heart failure: ICD recommended based on SCD-HeFT 3
Non-sustained VT ≥4 days post-MI with LVEF ≤40% and inducible VF/sustained VT at EP study: ICD warranted (Class B indication) 1
Non-Ischemic Cardiomyopathy (NICM)
ICD implantation for primary prevention is NOT recommended within the first 3 months after initial NICM diagnosis, as 70% of patients show significant LVEF improvement with optimal medical therapy. 2
First 3 months: ICD not recommended to allow time for medical optimization 2
3-9 months after diagnosis: ICD can be useful if recovery of LV function is unlikely 2
>9 months: Standard primary prevention criteria apply (LVEF ≤35% with NYHA II-III) 2
Special Consideration for NICM
Even after LVEF improves to >0.35, approximately 5.7% of patients still experience significant ventricular tachyarrhythmias, highlighting persistent risk 2
Disease-Specific Indications
Hypertrophic Cardiomyopathy
- Sudden death survivors and sustained VT patients require ICDs 1
Arrhythmogenic Right Ventricular Dysplasia (ARVD)
- Cardiac arrest survivors should receive ICDs 1
- Antiarrhythmic drugs are first-line for monomorphic VT; ICD reserved for drug failure 1
Idiopathic Dilated Cardiomyopathy
- Cardiac arrest survivors and sustained VT patients require ICDs with excellent prognosis given lack of coronary disease 1
Channelopathies
- Long QT syndrome, Brugada syndrome with high sudden death risk (especially family history of sudden death at young age) warrant prophylactic ICD 1, 4
Syncope with Dilated Cardiomyopathy
- ICD consideration warranted even without inducible arrhythmias, as these patients receive appropriate shocks 1
Pacing-Related Indications
In patients requiring urgent permanent pacing within 90 days of revascularization who meet primary prevention criteria (LVEF ≤0.35) and recovery is uncertain, implant an ICD with appropriate pacing capabilities initially to avoid subsequent upgrade procedures. 2
Upgrades from pacemaker to ICD carry 15.3% major complication rate versus 4.0% for simple generator replacement 2
For NICM <9 months requiring non-elective pacing with uncertain LV recovery: ICD with pacing capabilities recommended 2
Bridge to Transplant/LVAD Patients
ICD implantation is useful in outpatients awaiting transplant or with VAD who are not <40 days from MI 2
Patients with biventricular assist devices (BIVAD) generally tolerate even VF and are unlikely to derive survival benefit from ICD 2
Absolute Contraindications
Do NOT implant ICDs in the following scenarios: 1
- Terminal illness with life expectancy <6 months
- NYHA Class IV heart failure not eligible for transplantation
- Severe neurological sequelae following cardiac arrest
- Severe hemodynamic compromise without possibility of stabilization (unless bridge to transplant)
Timing Restrictions
Within 40 days of acute MI: ICD not indicated for primary prevention, as mortality during this period is primarily from pump failure, not arrhythmia 2, 1
Within 90 days of revascularization: Primary prevention ICD generally deferred unless specific high-risk features present 2
CABG Patch trial showed no benefit for prophylactic ICD immediately post-CABG, likely because acute ischemia was corrected 2