Alzheimer's Linked to Bypass Surgery
People with coronary artery disease who undergo heart bypass surgery have a significantly higher risk for developing Alzheimer's disease within five years than patients who have angioplasty, but "most patients will do very well and will not develop Alzheimer's disease" says Benjamin Wolozin, MD, professor of pharmacology at Boston University School of Medicine. His study shows that the risk for Alzheimer's disease is 70% higher in people with heart disease who undergo bypass surgery than in heart patients who undergo
angioplasty. He presented the findings at the 9th Annual International Conference on Alzheimer's Disease and Related Disorders.
The study examined patients 55 years and older with coronary artery disease and without dementia at the start of the study. They underwent either bypass surgery or angioplasty. The patients were then followed for nearly five years after surgery. Overall, the numbers of people with heart disease who develop Alzheimer's disease after surgery is "very small." Seventy-eight patients in over 5,000 bypass patients developed Alzheimer's disease, while 41 in almost 4,000 patients who had angioplasty developed Alzheimer's disease during the five years following surgery.
Other studies have reported memory and thinking problems after bypass surgery, but those problems occurred during the immediate postoperative period. The neurological problems were often associated with the use of a heart-lung bypass pump that circulates blood during the surgery. This is the first study to report an increased risk of Alzheimer's disease during a long-term follow-up period.
Wolozin says his study "has nothing to do with pumps. We are not suggesting that this effect is related to the use of the pump."
Rather, he says, he thinks "the problem is the surgery itself."
Wolozin says bypass surgery is comparable to a traumatic injury to the brain. "Surgical stress causes a steep increase in stress hormones, such as cortisone, and I think the stress hormones trigger a cascade of events that can also reduce oxygen to the brain."
Patient History Important
A major weakness of the study
"is that we don't know anything about the status of these patients before
surgery," says Marilyn Albert, PhD, director of the division of cognitive
neuroscience in the department of neurology at
To be included in the study, these patients had to have "no dementia," which is pretty vague, she says. "We don't know anything about the actual cognition and memory scores of the patients."
Albert, who was not involved in the study, says there is a great deal of interest in cognitive problems after bypass surgery.
"But all of the published studies so far have not established increased risk for Alzheimer's disease after surgery." Moreover, she says researchers using imaging technology to analyze the brains of bypass surgery patients and angioplasty patients report no differences.
But Martin Bednar, MD, PhD, the lead researcher of the study, disagrees.
"Several studies have demonstrated [loss of brain cells] after bypass surgery," he reports.
Bednar is a neurosurgeon and is senior director of clinical trials
at Pfizer Global Research and Development in Groton,
Stress, Low Oxygen, Plaques in Arteries May Increase Risk for Alzheimer's Disease
Steven T. DeKosky, MD, director the Alzheimer's Disease Research Center at the University of Pittsburgh, says that the study results are "not surprising, I would expect as much." He says a number of factors could cause injury to the brain -- tiny pieces of plaque that break off from clogged arteries in the heart could, for example, be carried to the brain where they could interrupt blood flow. Also, he says changes in blood pressure that occur when the patient is put on the heart-lung bypass machine could also cause "vascular damage that injures the brain." DeKosky was not involved in the study.
SOURCES: Martin Bednar,
MD, Pfizer Global Research and Development,
Steven T. DeKosky,
MD, director, Alzheimer's Disease Research Center,