Plasma amyloid β₄₂ and amyloid β₄₀ levels are associated with early cognitive dysfunction after cardiac surgery

Decreased cognitive function associated with coronary artery bypass graft (CABG) surgery is common. These deficits might be related to the cognitive dysfunction seen in the spectrum of mild cognitive impairment (MCI) to Alzheimer's disease (AD), which are the result of accumulation of amyloid beta (Aβ) peptide in the brain. We measured cognition both before and after CABG surgery and assayed Aβ levels to investigate whether the cognitive dysfunction of cardiac surgery was associated with Aβ levels. The plasma of 332 patients who had undergone neuropsychological testing before and 3 and 12 months after CABG surgery was analyzed for Aβ42 and Aβ40. Patients were classified as having pre-existing cognitive impairment (PreCI) if cognitive function was decreased in two or more tests compared with a healthy control group, and postoperative cognitive dysfunction (POCD) was defined as a decline in two or more tests compared with the group mean baseline score. PreCI was present in 117 patients (35.2%) and POCD in 40 (12%) at 3 months and 41 (13%) at 12 months after surgery. Both plasma Aβ42 and Aβ40 levels assessed before the CABG surgery were significantly decreased in patients who later had POCD at 3 months. Decreased preoperative plasma levels of Aβ42 and Aβ40 in patients who exhibit POCD at 3 months suggest that POCD at this time might share a common pathology with MCI/AD. This process might be exacerbated by anesthesia.