Frequency, predictors and prognostic impact of implantable cardioverter defibrillator shocks in a primary prevention population with heart failure and reduced ejection fraction.

INTRODUCTION: The role of the implantable cardioverter defibrillator (ICD) in primary prevention real-world population is debated. We sought to evaluate the incidence, predictors and prognostic impact of ICD shocks in consecutive heart failure patients implanted for primary prevention at our tertiary institution.

METHODS AND RESULTS: We retrospectively selected a sample of 497 patients (mean age 64.8 years, 82.1% men, average left ventricular ejection fraction, LVEF, 27.1%). At long-term follow-up (median time 70.4 months), total mortality was 40.8%, and 16.5% of patients had received at least one appropriate shock (3.12%/year). Inappropriate shock [odds ratio (OR) 1.93, 95% confidence interval (95% CI) 1.08-3.47; P = 0.027] and length of follow-up (1 year, OR 1.01, 95% CI 1.00-1.01; P = 0.0031) were associated with the occurrence of appropriate shock, whereas atrial fibrillation (OR 2.65, 95% CI 1.55-4.51, P < 0.001), length of follow-up (1-year OR 1.01, 95% CI 1.00-1.01, P < 0.001) and appropriate shock (OR 1.93, 95% CI 1.08-3.47, P = 0.027) were associated with the occurrence of inappropriate shock. Neither appropriate nor inappropriate shock independently increased mortality risk, whereas older age (hazard ratio 1.05; 95% CI 1.04-1.07; P < 0.001), atrial fibrillation (hazard ratio 2.25; 95% CI 1.67-3.02; P < 0.001) and lower LVEF (hazard ratio 0.97; 95% CI 0.94-0.99; P = 0.004) did.

CONCLUSION: Incidence of shocks in real-world primary prevention ICD recipients might be lower than expected, and the association between ICD shocks and prolongation of survival is not as clear-cut as might be perceived. Further investigations from larger real-world samples are warranted.