Cognitive impairment before and six months after cardiac surgery increase mortality risk at median 11 year follow-up: a cohort study

Background The additive effects of cognitive impairment and depression on mortality risk after cardiac surgery are unknown. Methods Patients were assessed on a battery of six neurocognitive measures before cardiac surgery (N = 521) and at six month follow up (N = 377/521, 72.4%). Cognitive impairment classification was based on cognitive test scores 1 SD below age and sex matched normative data, and classified according to amnestic, non-amnestic and mixed cognitive impairment subtypes. Survival analyses entered cognitive impairment subtypes and depression interactions terms adjusted for 12 common risk factors. Results There were 5407 person years for analysis (median 11.1 year survival, interquartile range of 7.9 to 13.1) and 176 deaths (33.8%) by the census date. Before cardiac surgery, patients with a mixed-cognitive impairment (adjusted hazard ratio (HR) = 2.53; 95% confidence interval (CI), 1.57-4.06, p <.001) and non-amnestic cognitive impairment (adjusted HR = 1.51; 95%, 1.00-2.32, p =.05) were at greater mortality risk. Six month analyses corroborated that the mixed-cognitive impairment group were at higher mortality risk (adjusted HR = 2.35; 95% CI, 1.30-4.25, p =.005). When change in neurocognitive functioning over time was analyzed, a higher mortality risk was evident only amongst patients with cognitive impairment evident at baseline and six months (adjusted HR = 1.83; 95% CI, 1.08-3.10, p =.03). No cognition by depression interaction term was significant. Conclusions These data suggest that a mixed cognitive impairment subtype, and continuing cognitive impairment before and six months after cardiac surgery, is associated with long term mortality, independent of depression and common risk factors.