Shocks burden and increased mortality in implantable cardioverter-defibrillator patients.

Background: Implantable cardioverter-defibrillator (ICD) shocks are associated with an increased risk of death. It is unclear whether ICD shocks are detrimental per se or a marker of higher risk patients.

Objective: We aimed to assess the association between ICD shocks and time to death after correction for baseline mortality based on the Seattle Heart Failure Model (SHFM).

Methods: The primary analysis compared time-to-death between patients receiving no shocks and patients receiving shocks of any type adjusted for SHFM score at time of implantation and other comorbidities. Subgroup analyses were performed to further describe the relationship between shocks and mortality risk.

Results: Over a median follow-up of 41 months (interquartile range 23-64), one or more shock episodes occurred in 59% of 425 patients and 40% of the patients died. Patients receiving shocks of any type had increased risk of death (hazard ratio 1.55; 95% confidence interval 1.07-2.23; P = .02) versus patients receiving no shocks. While patients with 1-5 days with shock (shock days) did not show evidence of increased risk of death (1.30 [0.88-1.94]; P = 0.19), those with 6-10 shock days (2.22 [1.21-4.08]; P <.01) and >10 shock days (3.66 [1.86-7.19]; P <.01) had increasingly higher risk. There was no increased hazard for death (0.73 [0.34-1.57]; P = .41) in patients treated only with antitachycardia pacing (ATP).

Conclusion: ICD shocks were associated with increased mortality risk after adjustment for SHFM-predicted mortality, and the burden of shocks played a role in this association. ATP did not increase mortality risk, suggesting that shocks may themselves be detrimental.