Implantable cardioverter-defibrillator shock prevention does not reduce mortality: a systemic review

Mortality is increased among implantable cardioverter-defibrillator (ICD) recipients who receive shocks; however, whether shocks cause this increase or are simply a marker of risk is unknown. Antiarrhythmic medications, catheter ablation, and enhanced ICD programming all may reduce ICD shocks, but whether shock reduction decreases mortality is unknown.

The purpose of this study was to conduct a meta-analysis to estimate the impact of ICD shock reduction on survival.

Two independent reviewers searched MEDLINE, EMBASE, and clinicaltrials.gov and extracted data from randomized controlled trials assessing the efficacy of interventions to prevent ICD shocks.

Seventeen randomized trials were included in this analysis, including 5875 patients. Mean ejection fraction of all trial participants was 32%, and 25% of the patients received ICD therapy for primary prophylaxis. Antiarrhythmic medications (odds ratio [OR] 0.59, 95% confidence interval [CI] 0.36-0.96, P = .03) and catheter ablation of ventricular tachycardia (OR 0.35, 95% CI 0.19-0.62, P = .0004) significantly reduced the proportion of patients receiving shocks. However, there was no significant reduction in mortality among trials of antiarrhythmic medications (OR 1.07, 95% CI 0.72-1.59, P = .73) or catheter ablation (OR 0.72, 95% CI 0.32-1.64, P = .44). The 5 ICD programming trials had sufficiently heterogeneous interventions that pooling of their results was not performed. However, only the PAINFREE-II (Pacing Fast Ventricular Tachycardia Reduces Shock Therapies) trial demonstrated a significant reduction in shocks (OR 0.38, 95% CI 0.22-0.65), but this was not associated with any significant reduction in mortality (OR 1.41, 95% CI 0.81-2.45).

There is no compelling evidence that existing interventions that reduce ICD shocks significantly improve survival.