By JOHN FAUBER
July 19, 2004
Philadelphia - For years, doctors have known that many people who undergo heart surgery experience temporary memory problems, but a provocative new study suggests they also may be at greater risk for developing Alzheimer's disease.
Looking at a group of about 9,000 people who underwent either coronary artery bypass graft or angioplasty, researchers found that bypass surgery increased the risk of later developing Alzheimer's by 70%.
Marilyn Albert, a Alzheimer's researcher who was not involved in the study, said the findings were "very surprising."
"People who have (bypass surgery) often complain that they are not normal afterward," said Albert, director of the division of cognitive neuroscience at Johns Hopkins University School of Medicine. "Everybody's worried about the cognitive problems of surgery."
The new finding, believed to be the first study tying bypass surgery to Alzheimer's, was presented Monday at the ninth International Conference on Alzheimer's Disease and Related Disorders of the Alzheimer's Association.
Several studies have found that patients who undergo heart surgery may experience memory problems that usually go away in a few months.
"Memory loss after (bypass surgery) is well known," said Steven DeKosky, an Alzheimer's researcher at the University of Pittsburgh Medical Center.
DeKosky, a professor of neurology who is not involved in the study, speculated that people who already are at risk for Alzheimer's and then undergo heart surgery may suffer additional damage to the brain that accelerates the onset of dementia.
"All you may be doing is making worse a system that was destined to fail," he said. "The concept makes sense."
Even though the study's findings are disturbing, he said he would not recommend people avoid heart surgery.
"(The finding) is very preliminary," DeKosky said.
The study, conducted by researchers at Pfizer Inc., Loyola University Medical Center in Maywood, Ill., and the Hines Veterans Administration Hospital in Hines, Ill., compared 5,216 people who had bypass surgery and 3,954 people who had angioplasty in 1996 and 1997.
Over the course of up to six years, 119 of them were diagnosed with Alzheimer's - and 78 of those had had bypass surgery.
The study's authors offered several explanations for the finding: detrimental changes in blood flow and blood pressure as a result of being on a heart-lung machine may cause brain cells to die; stress hormones that can be damaging to the brain also may increase during surgery; and, in addition, tiny clots may break off from arteries and fat during surgery and travel downstream to the brain.
"We think it's the stress and trauma of the surgery," said co-author Benjamin Wolozin, a professor of pharmacology at Boston University Medical Center.
Wolozin, a former Loyola University researcher, said he did not think the increased Alzheimer's risk was due to the effects of anesthesia. In fact, some research suggests that anesthesia and other types of surgery actually may help protect against temporary cognitive decline.
Co-author Martin Bednar said he believed people who are predisposed to Alzheimer's may suffer the loss of brain cells during surgery, which in turn lowers their reserve brain function.
"If you tap into that reserve, your chances of being diagnosed with Alzheimer's are increased," said Bednar, senior director of Pfizer Global Research & Development. Pfizer now is working to develop drugs that may protect the brain during heart surgery, Bednar said.
He said bypass surgery is beneficial for many people, but he believes it can be made even better.
"There's a half a million people a year who have bypass surgery," he said. "What we really want to do is bring attention to an issue. We think this is a big deal."Second study also presented
However, the issue is likely to remain controversial, especially in light of a second study done by researchers at the Mayo Clinic suggesting that bypass surgery is not a major risk factor for developing dementia.
That study, which covered a five-year period in the early 1990s, also was presented at the Alzheimer's conference.
Bill Thies, vice president of medical and scientific affairs at the Alzheimer's association, said the issue is likely to remain unresolved for a while.
"It's a great debate," Thies said. "We'd like to know if you should give different advice (about heart surgery) to someone who has a family history of Alzheimer's disease."
It is possible that bypass surgery is not responsible for the increased risk, Thies added, but rather it is the overall vascular health of people who undergo the surgery compared with those who receive the less-invasive angioplasty procedure.