Ventricular Tachycardia Prophylaxis in Structural Heart Disease
For adults with structural heart disease (ischemic or non-ischemic cardiomyopathy) and LVEF ≤35%, ICD implantation is the recommended prophylaxis, but only after waiting at least 40 days post-MI and 90 days post-revascularization. 1
Primary Prevention ICD Indications Based on LVEF and Clinical Status
The most recent 2025 ACC/AHA guidelines provide clear thresholds for prophylactic ICD implantation in patients with structural heart disease 1:
Class I Recommendation (Strongest Evidence)
- LVEF ≤30% with NYHA Class I, II, or III symptoms 1
- LVEF 31-35% with NYHA Class II or III symptoms 1
- LVEF ≤40% with inducible VT at electrophysiologic study 1
All patients must have expected survival ≥1 year and be at least 40 days post-MI and 90 days post-revascularization 1.
Critical Timing Considerations
Do not implant an ICD in the early post-MI period (first 40 days) for primary prevention, as this has not shown survival benefit. 1 The DINAMIT trial demonstrated that while ICD implantation 6-40 days post-MI reduced arrhythmic deaths by 58%, this was offset by increased non-arrhythmic deaths, resulting in no overall mortality benefit 1.
Exception for Early ICD Consideration
For patients with clinically relevant ventricular arrhythmias occurring >48 hours but within 40 days post-MI, ICD implantation is reasonable (Class IIa recommendation). 1 These sustained arrhythmias occurring after the acute phase carry increased mortality risk distinct from transient ischemia-related arrhythmias 1.
Electrophysiologic Study-Guided Approach
For patients with LVEF ≤40% and non-sustained VT ≥4 days post-MI, electrophysiologic testing should be performed 1. If sustained VT is inducible and not suppressible with antiarrhythmic drugs (particularly procainamide), ICD implantation is indicated 1.
This approach, validated by the MADIT and MUSTT trials, identifies a high-risk subset representing only 3.2% of post-MI survivors but with substantial modifiable mortality risk 2. The MUSTT trial demonstrated a 76% reduction in cardiac arrest or arrhythmic death (relative risk 0.24,95% CI 0.13-0.45) with EP-guided ICD therapy 2.
Non-Ischemic Cardiomyopathy
The same LVEF thresholds apply to non-ischemic dilated cardiomyopathy. 1 The Defibrillators in Nonischemic Cardiomyopathy Treatment Evaluation trial showed mortality reduction from 14.1% to 7.9% over 2 years with ICD therapy in patients with LVEF ≤35% 1.
Secondary Prevention (Post-Arrest or Sustained VT)
ICD implantation is the first-line treatment for survivors of cardiac arrest or hemodynamically unstable sustained VT (Class I-A indication) 1. The AVID trial demonstrated 31% mortality reduction with ICD versus amiodarone over 3 years 1, and meta-analysis of three major trials showed relative risk reduction of 0.27 (95% CI 0.11-0.41) over 6 years 1.
For sustained VT without hemodynamic compromise:
Contraindications and Exceptions
Do not implant ICD if:
- VT/VF due to transient, reversible causes (electrolyte imbalance, acute ischemia, drug toxicity) 1
- Life expectancy <6 months from non-cardiac disease 1
- NYHA Class IV heart failure without transplant candidacy 1
Important caveat: Even with apparent reversible causes, the AVID registry suggests future arrhythmic risk remains elevated, so clinical judgment is required 1.
Role of Catheter Ablation
Catheter ablation should be considered for recurrent monomorphic VT despite ICD and antiarrhythmic therapy. 1 The VANISH trial showed 28% relative risk reduction in death, VT storm, and appropriate ICD shocks with ablation versus escalated drug therapy in patients with VT despite first-line antiarrhythmic drugs 3.
For VT occurring despite amiodarone specifically, catheter ablation is superior to more aggressive drug therapy 3. However, ablation is adjunctive to ICD therapy, not a replacement for primary prevention 1.
Wearable Cardioverter-Defibrillator
The usefulness of temporary wearable cardioverter-defibrillators in patients with LVEF ≤35% early post-MI is uncertain (Class IIb). 1 This may serve as a bridge during the mandatory 40-day waiting period, but evidence for survival benefit is limited.
Common Pitfalls to Avoid
- Do not use LVEF alone without considering timing post-MI/revascularization – the 40-day and 90-day waiting periods are mandatory for primary prevention 1
- Do not withhold ICD in patients with LVEF 31-35% who have NYHA Class II-III symptoms – this is a Class I indication 1
- Do not assume VT in the first 48 hours post-MI requires ICD – these are typically ischemia-related and do not predict long-term risk 1
- Do not implant ICD without confirming expected survival ≥1 year – device therapy requires sufficient longevity to realize benefit 1