A Systematic Review and Meta-analysis of the Association Between Implantable Cardioverter-Defibrillator Shocks and Long-term Mortality

Background: It is unknown whether implantable cardioverter-defibrillator (ICD) discharges actively contribute to a worse prognosis independent of the underlying arrhythmia. There is considerable variability in the reported risk of mortality after appropriate and inappropriate ICD shocks. The aim of our systematic review was to provide a reliable effect size of the association between ICD shock and mortality for both types of therapies. Methods: On the basis of a systematic literature search, 10 studies were considered eligible for inclusion in the analysis, and data on the hazard ratio (HR) of mortality after ICD shock were extracted from each study. Results: On pooled analysis, a substantial difference was detected in the risk for subsequent mortality between appropriate and inappropriate shocks. Among patients receiving an appropriate ICD shock, the HR for cardiac death was 2.95 (95% confidence interval [CI], 2.12-4.11; P < 0.001) compared with an HR of 1.71 (95% CI, 1.45-2.02) for those receiving an inappropriate shock. Clinical variables like ejection fraction, New York Heart Association class, and length of follow-up did not affect the HRs in our meta-regression models. Conclusions: Our analysis showed a significant association between appropriate and inappropriate ICD shocks and mortality, with a stronger association for appropriate shocks. Previous trials of ICD therapy reduction programming have shown a significant reduction of inappropriate shocks. The management of appropriate shocks is more challenging and may be optimized by the assessment and treatment of the underlying ventricular arrhythmias. The role of therapies aimed at modifying the arrhythmic substrate and the potential impact on ICD shocks and mortality requires further investigation.