More than half of people who undergo cardiac bypass surgery experience memory problems and other cognitive deficits immediately after surgery. Usually, such problems fade within weeks or months. But recent research indicates heart-bypass patients who show significant cognitive decline immediately after surgery are more likely to show similar decline five years later--even when cognitive function had returned to normal within six months of surgery.
In the study, published in the Feb. 8 New England Journal of Medicine (Vol. 344, No. 6), a team of Duke University researchers led by cardiothoracic anesthesiologist Mark F. Newman, MD, examined 261 patients who had elective coronary-artery bypass grafting (CABG). The patients' average age was 61.
Before surgery and on several later occasions, the researchers gave patients a battery of cognitive tests, measuring their verbal and visual memory, language comprehension, spatial ability, attention and concentration abilities. Results showed that 53 percent of patients experienced significant cognitive declines shortly after surgery. Six weeks later, 36 percent were impaired, and after six months, 24 percent.
Five years after surgery, however, the incidence of cognitive decline had risen again, to 42 percent. Long-term decline was more common for patients who were older, were less educated or experienced cognitive decline immediately after surgery.
"Adjectives such as 'subtle,' 'transient,' and 'subclinical' have been used to describe the cognitive decline that occurs after CABG but such descriptions minimize the importance of these changes to clinicians, patients, and their families," the study authors write.
Stanton P. Newman, DPhil, a health psychologist at University College London who also studies cognitive effects of bypass surgery, says the finding is very important because it demonstrates long-term effects, but it "raises questions about the mechanisms for the long-term changes."
One possible explanation is that bypass surgery itself causes cognitive impairment in some patients. For example, small pieces of matter or air that travel to the brain during surgery, such as coronary-artery plaque, may block vessels in the brain, causing immediate and long-term cognitive decline. And previous research has suggested that using a heart-lung pump during bypass surgery can also increase the danger of brain injury.
Alternatively, some people who undergo bypass surgery--including older patients and those who have arteriosclerosis in the blood vessels of the brain--may be more vulnerable to cognitive decline from the outset. For those people, any small insult to the brain during surgery may trigger an immediate decline after surgery. Although such people typically show improvement soon after surgery, the immediate decline may reflect a general vulnerability that manifests itself more clearly later.
In an editorial accompanying the study, Ola A. Selnes, PhD, and Guy M. McKhann, MD, of Johns Hopkins University, argue that there's only one way to settle the question of whether the surgery causes long-term decline: by comparing heart-bypass patients with patients who have similar cardiovascular risk factors and symptoms, but who do not have surgery. Such research is under way, they note, but the results aren't due for at least two years.
Meanwhile, Duke's Mark Newman concludes, "I wouldn't want people to be scared away from a procedure that may be life-saving for them. We're trying to make a safe operation safer."
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