Among the many factors involved in deciding how to treat coronary artery disease, physicians must evaluate overall outcomes and the potential for complications. Some studies have found that cognitive decline and neurologic complications, such as stroke, have been associated with coronary artery bypass surgery. A new study finds no evidence that bypass patients have a greater risk of long-term cognitive decline than patients not undergoing surgery. The study is published in the May 2008 issue of Annals of Neurology (http://www.interscience.wiley.com/), the official journal of the American Neurological Association.
Led by Ola A. Selnes and Guy M. McKhann of the Johns Hopkins University School of Medicine, the study involved 152 patients who had bypass surgery and 92 patients with coronary artery disease who did not have surgical intervention. Patients underwent a series of memory and other cognitive tests at the beginning of the study period, and after 3, 12, 36 and 72 months. Of these, 96 bypass patients and 61 control patients completed cognitive testing after six years.
The results showed that there were no significant differences in cognitive scores between the two groups at the beginning of the study. Both groups showed modest decline in cognitive performance during the study period, but there were no significant differences in the degree of decline between the groups after six years.
The authors point out that the bypass patients had conditions that might be associated with worse cognitive performance, including higher incidence of cardiovascular risk factors, more severe coronary artery disease and more surgery requiring general anesthesia during the follow-up period. Despite these factors, no differences between the two groups were found. While other studies have looked at the long-term effects of bypass surgery on cognitive function, this is the first prospective long-term study comparing cognitive outcomes of bypass patients to cardiac patients who did not have surgery.
The lack of any difference in the long-term cognitive trajectories between the surgery patients and our study controls suggests that late cognitive decline 5 or more years after CABG is not specific to the use of cardiopulmonary bypass, the authors state.
As to why cognitive changes occurred in both groups, there is evidence that patients with risk factors for vascular disease (such as high blood pressure) and markers of atherosclerosis (hardening of the arteries) have higher rates of cognitive decline over time than patients without these risk factors. The authors note that since both groups in the study had such risk factors, it is likely that the cognitive decline is related either to normal aging in the context of cardiovascular disease or to progression of the underlying vascular disease over time. More studies are needed, however, to determine if better control of these risk factors would lessen the degree of cognitive decline in patients with coronary artery disease.
The authors note that the study emphasizes the importance of including control subjects when studying long-term cognitive outcomes after surgical procedures. They conclude that the risk of late cognitive decline should not be a consideration when choosing between types of intervention for coronary artery disease.