April 2011

Document Type


Degree Name



Dept. of Physiology and Pharmacology


Oregon Health & Science University


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 co-morbidities. Subgroup analyses were performed to further describe the relationship between shocks and mortality risk. Results: Over a median follow-up of 41 (IQR 23-64) months, ≥1 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=0.02) versus patients receiving no shocks. While patients with 1-5 days with shock (shockdays) did not show evidence of increased risk of death (1.29 [0.87-1.92]; P=0.20), those with 6-10 shockdays (2.37 [1.31-4.28]; P<0.01) and >10 shockdays (3.66 [1.86-7.20]; P<0.01) had increasingly higher risk. There was no increased hazard for death (0.73 [0.34-1.57]; P=0.42) in patients treated only with antitachycardia pacing (ATP). Conclusion: ICD shocks were associated with increased mortality risk after adjustment for SHFM predicted mortality and both dose and timing of shocks played a role in this association. ATP did not increase mortality risk suggesting that shocks may be themselves detrimental.




School of Medicine



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