Analysis of 22,349 coronary artery disease patients reveals that coronary artery bypass graft (CABG) surgery associates with a 23% increased risk of cognitive impairment, including mild cognitive decline and dementia. The effect proved most pronounced in carriers of the APOE ε2/ε3 genotype, showing a 91% elevated risk compared to other genetic variants. This finding challenges the assumption that revascularization procedures uniformly benefit brain health through improved circulation. The cognitive risks may stem from surgical factors like anesthesia exposure, cardiopulmonary bypass-induced inflammation, or microemboli during the procedure. However, the observational design cannot establish whether surgery directly causes cognitive decline or whether sicker patients requiring bypass already face higher dementia risk. The APOE genotype interaction suggests personalized surgical decision-making may become important, as this gene variant affects both cardiovascular outcomes and Alzheimer's disease susceptibility. Since this remains an unreviewed preprint, these results require peer review and replication before influencing clinical practice. The study represents incremental progress in understanding surgery-brain connections but highlights the complex interplay between cardiovascular interventions and cognitive preservation in aging populations.