The link between CABG surgery and development of long-term cognitive decline has been controversial in medical literature.
"What we found is that in an observational study of residents of Rochester, Minn., CABG surgery was not a risk factor for dementia," says David Knopman, M.D., Mayo Clinic neurologist and the study's lead investigator. "It was reassuring that the surgery was not associated with increased risk of dementia."
This study took a unique approach to this disputed topic. "In the literature on the long-term outcome of CABG surgery, most work focuses on those who have had the surgery, but there often isn't a suitable comparison group," says Dr. Knopman. His study started with dementia patients and worked backward to find out whether these patients were more likely to have previously undergone CABG surgery and compared them to the rate of CABG surgery in a non-demented control group.
Dr. Knopman explains that his patients often raise the issue of a dementia-heart surgery connection. "Patients often say, 'My memory problems began after my heart surgery, even though I didn't have any obvious complications of the surgery,'" he says.
Now, Dr. Knopman says he can respond that his study indicates that the heart surgery did not directly cause the memory issues. Memory problems may be due to complications experienced as a result of the CABG surgery, though, he says. However, if a patient had no complications due to the surgery, Dr. Knopman would look to other causes of the memory disorder rather than the bypass surgery.
The question, then, says Dr. Knopman, has been, "Could the CABG have a long-term consequence, even if the patients recovered without incident?
"It's been thought that perhaps the bypass procedure itself, whether it caused acute confusion or not, could damage the brain and reduce the cerebral reserve for being able to tolerate future diseases," says Dr. Knopman. "The arterial blood going from the heart to the brain is being manipulated in CABG surgery; it has the added potential for causing embolization from heart to head. Our findings do not support uncomplicated CABG surgery causing later dementia."
Dr. Knopman indicates that his study does not discount the existence of short-term cognitive issues post-bypass surgery. "Our study doesn't at all speak to short-term cognitive problems and CABG surgery -- that wasn't what we studied, and we can't comment about that at all from this research," he says.
The researchers used the Rochester Epidemiology Project medical records linkage system to identify dementia cases for 1990-1994. Dementia was defined by the criteria of the Diagnostic and Statistic Manual for Mental Disorders, Fourth Edition; postoperative confusion that later ceased was excluded. All dementia cases were then matched by age and sex to control cases that were dementia-free in the year of dementia onset in the dementia cases. In the five-year period studied, there were 564 dementia cases. Of these, 21 had undergone CABG before developing dementia. In the control group, 23 people had undergone CABG surgery.
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