Prognostic Importance of Defibrillator Shocks in Survivors of Sudden Cardiac Death

Implantable cardioverter-de fi brillator (ICD) implantation is standard of care for patients who have survived life threatening ventricular tachyarrhythmias (LTVA). ICD shocks predict future adverse events in patients with ICD implantation for primary prevention. However, the role of ICD shocks in prediction of adverse events in a secondary prevention population is unknown. The Antiarrhythmics Versus ICDs (AVID) Trial (n=1016) was a randomized controlled trial comparing ICD (n=507) and antiarrhythmic drugs (n=509) in the treatment of patients with LTVA. Mean follow-up duration was 916 ± 471 days. We analyzed the ICD arm of the AVID trial using the NHLBI limited access dataset. ICD shocks were categorized as appropriate if underlying rhythm triggering the shock was ventricular tachycardia or ventricular fibrillation. All other ICD shocks were considered as inappropriate. Data on ICD therapy was available for 420 patients. Any shock (n=380), any appropriate (n=296) or any inappropriate (n=72) shock was not associated with increased all cause, cardiac or arrhythmic mortality. However any appropriate shock was associated with increased LTVA. In conclusion, ICD shocks do not confer increased risk of death on follow up in LTVA survivors. Use of ICD shocks as surrogate marker for adverse outcomes is not viable in secondary prevention patients.