Appropriate Therapy But Not Inappropriate Shocks Predict Survival in Implantable Cardioverter Defibrillator Patients

Background: Inappropriate implantable cardioverter defibrillator (ICD) shocks have been linked to a worse clinical outcome due to direct myocardial injury. Hypothesis: The occurrence of ventricular tachyarrhythmia indicating progression of the underlying heart disease, but not the ICD shock itself, has prognostic impact in clinical routine. Methods: In a retrospective study, 1117 recipients of an ICD were analyzed with respect to appropriate and inappropriate therapies and survival. Results: During a mean follow-up of 2.92 years, appropriate therapy occurred in 27.7% and 54.0% of patients who had received an ICD for primary and secondary prevention of sudden cardiac death (SCD), respectively (P < 0.0001). Inappropriate shock therapy occurred in 15.0% and 25.4% of patients who had received an ICD for primary and secondary prevention of SCD, respectively (P = 0.122). Appropriate ICD therapy had a strong impact on overall survival (P < 0.0001), and this association was found both in primary (P < 0.0001) and secondary (P = 0.002) prevention of SCD. Inappropriate ICD shocks had no impact on total mortality, neither in primary nor secondary prevention of SCD. Conclusions: Inappropriate shocks do not affect survival, in strong contrast to appropriate ICD therapy. Our study does not support the hypothesis that shock therapy in itself worsens clinical outcome. However, it confirms that appropriate ICD therapy is a warning sign and should prompt physicians to consider additional treatment strategies.