Cognitive Dysfunction Influences Mortality Risk After Heart Surgery

Barbara Boughton

September 20, 2010

September 20, 2010 (San Francisco, California) — Cognitive health — particularly in language and visual memory — seems to predict the risk for mortality after heart surgery even 8 or more years later, according to new research unveiled at the American Neurological Association 135th Annual Meeting.

In this observational study, the cognitive outcomes of patients undergoing coronary artery bypass graft surgery were compared with controls with coronary artery disease under medical management and those who were heart healthy.

Results of the study, which enrolled 388 patients, indicated that after an average follow-up of 8.8 years, overall survival after bypass was worst among those who scored the lowest on cognitive tests.

"What we found is that those who had the best cognitive function had the best survival," said lead study author Rebecca Gottesman, MD, PhD, assistant professor in the Cerebrovascular Division of the Department of Neurology at Johns Hopkins School of Medicine, Baltimore, Maryland. "So cognitive dysfunction is probably a marker for some other health problems — perhaps early Alzheimer's disease or having had small strokes in the brain."

It is important to keep cognitive dysfunction in mind when assessing prognosis, Dr. Gottesman added. "Patients who have cognitive problems may have worse health outcomes — and not just because they are elderly."

Preoperative Dysfunction

Previous studies have shown that people who undergo coronary artery bypass graft surgery have preoperative cognitive dysfunction, and the researchers initiated the study to see what influence such dysfunction might have on survival outcomes, Dr. Gottesman said.

"There have been anecdotal reports showing that people who have cognitive impairment seem to die earlier than those who don't," she said. "The question is, 'Is this because they are older or is there some other kind of health problem that is influencing mortality?'"

In the study, cognitive testing in 8 domains was administered to patients undergoing coronary artery bypass procedures before surgery, to controls with cardiovascular disease treated with medical management, and to heart-healthy controls at baseline.

Overall mortality rates based on quartiles of global cognitive performance were 34%, 26%, 25%, and 20% for the lowest cognitive scores to the highest.

Low performance in visual memory tasks (P = .0003) and language (P = .01) was particularly likely to influence survival. Low scores on motor speed (P = .08) and psychomotor speed (P = .06) also showed a trend toward increased risk for mortality, although these results did not reach statistical significance.

Baseline demographics of the entire cohort, including the medical and heart-healthy controls, showed an elevated incidence of hypertension (51%) and myocardial infarction (41%). The mean age of the cohort at baseline was 64.4 years.

To further understand the mechanisms behind the association of cognitive dysfunction and mortality, the researchers plan to analyze the observational cohort for potential confounders, such as underlying cerebrovascular disease, Dr. Gottesman said.

"We'd like to know if there is some kind of degenerative process going on as opposed to just cerebrovascular disease," she said.

Interesting Questions, Potential Flaws

Although the study raises some interesting questions, it also has some potential flaws, commented Jacob DeLaRosa, MD, chief of cardiovascular surgery at Idaho State University Portneuf Medical Center in Pocatello.

"The study does make sense because patients with atherosclerotic disease don't just have disease in the heart, but also in the brain and the legs. It's not just a local disease, but a systemic problem, and patients who are sicker just have more health problems," he said.

Yet Dr. DeLaRosa noted that the study would have been more illuminating if it had compared patients undergoing coronary artery bypass procedures to those who had other types of surgical intervention, rather than medical management for cardiovascular disease. "It's important to compare apples to apples," he said.

He also noted that the study did not spell out the specifics of the coronary artery bypass procedures that some patients in the study underwent. Type of heart surgery might have influenced cognition and mortality, because patients who receive cardiopulmonary bypass during surgery as opposed to those who have surgery with a beating heart may lose brain cells, he said.

The study was supported by the National Institutes of Health and the Dana Foundation. Dr. Gottesman and Dr. DeLaRosa have disclosed no relevant financial relationships.

American Neurological Association (ANA) 135th Annual Meeting: Abstract M-36. Presented September 13, 2010.


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