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.

Conclusion: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.