Heart surgery does not induce cognitive decline
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Coronary artery bypass grafting (CABG) is not a major risk factor for either short- or long-term cognitive decline or dementia, according to two reports in the journal Neurology. The widespread assumption that a decline in cognition occurs after CABG is apparently based on studies that did not include comparable control groups.
To rectify this limitation, researchers at Johns Hopkins University in Baltimore, led by Dr. Guy M. McKhann, prospectively followed patients who had undergone CABG. One hundred forty had conventional bypass surgery, in which the heart is stopped and a heart-lung machine is used to circulate blood during the operation; and 72 patients underwent “off-pump” bypass surgery, during which only a portion of the heart is immobilized.
In addition, 99 patients with similar degrees of coronary artery disease were treated with drugs, and 69 were healthy “control” subjects, matched to the treatment groups by age, gender and education level.
McKhann’s group administered a battery of neuropsychological tests before the study began, at 3 months and at 12 months after treatment. Before treatment, the three groups with coronary artery disease scored significantly lower than the healthy controls in all eight cognitive categories.
All four groups exhibited similar degrees of improvement in cognition after 3 months and 12 months, but those with coronary artery disease remained proportionately lower compared with the healthy controls.
“Thus,” the authors write, “during this 12-month follow-up, there was no statistical evidence of cognitive decline in any of the coronary artery disease groups as compared to each other or the heart-healthy controls.”
The perceived decrements in cognition can therefore be attributed to cognitive impairments as a result of cerebrovascular disease before surgery, they suggest.
In the second paper, Dr. D. S. Knopman and colleagues at the Mayo Clinic College of Medicine in Rochester, Minnesota, performed a study that included patients with dementia and healthy controls individually matched by age and gender (557 subjects in each group).
Twenty-four patients in the dementia group and 28 in the control group had undergone CABG prior to the onset of dementia. The results were similar for analyses restricted to Alzheimer’s diseases cases and their matched controls.
“Our null result suggests that CABG surgery did not cause subclinical brain disease, and did not predispose patients to later dementia or Alzheimer’s disease,” Dr. Knopman’s team concludes.
“The results may temper the neurologists’ concern over the safety of (CABG)—important because many of our patients are at risk of cardiovascular disease,” Dr. Wade S. Smith, from the University of California, San Francisco, and Dr. Mark Mapstone, from the University of Rochester in New York, write in an accompanying editorial.
SOURCE: Neurology, October 11, 2005.
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