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Study links bypass surgery to mental decline
©New York Times © St. Petersburg Times, published February 8, 2001 Five years after heart bypass surgery, 42 percent of patients show a significant decline on tests of mental ability, probably from brain damage caused by the surgery, doctors from Duke University say in a new study. Older patients and those who experienced a drop in test scores soon after surgery were most likely to show declines five years later, the study found. The report, being published today in the New England Journal of Medicine, has evoked mixed reactions among experts. On one hand, they say that a lowered test score does not necessarily mean a person is mentally impaired and that the 42 percent figure may needlessly frighten patients away from surgery that can save their lives. On the other hand, researchers say that the study is well-prepared and that it highlights an ugly truth that surgeons know but are not eager to discuss with patients: Some patients do wind up mentally impaired after bypass surgery. Doctors are not sure why, though they suspect various factors that interfere with blood flow to the brain during surgery. The findings also seem likely to fuel the debate about whether all bypass operations each year in the United States are necessary, or whether more patients with blocked arteries, particularly older people, should be treated with medication or less invasive procedures to open clogged blood vessels. The researchers are not the first to link mental decline to bypass operations. But earlier studies were shorter term, and many doctors hoped that the cognitive losses would be temporary. The new study is the first to show lasting changes in so many patients so long after the surgery. The study, based on 261 patients who had bypass surgery at Duke from 1989 to 1993, relied on mental tests performed before surgery and then six weeks, six months and five years later. The average age of the patients was 61, with a range of 50 to 71. Patients were considered to have declined mentally if their test performance at five years was at least 20 percent lower than their score before surgery. A 20 percent drop was similar to the difference in function between subjects at ages 40 and 60. The drop in scores in the bypass patients could not be attributed to aging, the authors said, because it was more than two to three times the mental decline found in 5,888 Medicare patients who did not have bypass surgery and whose cognitive abilities were followed for five years in a separate study. A doctor not associated with the study, William A. Baumgartner, chief of cardiac surgery at Johns Hopkins Hospital, said researchers at his hospital were also studying the problem but had found far fewer patients with significant long-term problems, perhaps 8 percent to 10 percent. "I was shocked at the 42 percent," Baumgartner said. "We just haven't seen that in our five-year follow-up. People who read this thing are going to be scared out of their minds that they're going to be some kind of invalid. In our series, that is clearly not the case. They need further work to see how this affects the well-being of patients." Dr. Mark F. Newman, an author of the study and chief of cardiothoracic anesthesiology at the Duke Medical Center, said he and his colleagues were not sure how many of the patients themselves were troubled by their declines or even aware of them, since the changes might not have caused problems in their daily lives. "For someone who is working, it may be very devastating," Newman said. "For others, it might just be annoying." But Newman said he hoped the findings would not lead patients to shun bypass surgery. "In a lot of patients, we prolong their life," he said. "We have to continue working on improving the quality of their life as well." Several elements of a bypass have the potential to cause brain damage, Newman said. One is the heart-lung machine, through which the patient's blood is circulated to pick up oxygen. Doctors suspect that air bubbles produced by the machine may block blood flow through minute vessels inside the skull, killing brain cells. The machine may also pump droplets of fat released from the surgical site to the brain, where they can cause the same problem as air bubbles. It is also possible that the machine does not provide enough oxygen for some patients, and that lack of oxygen can also injure brain cells. The other possible source of trouble is fatty deposits in the patient's own aorta. Surgeons clamp it and may sew blood vessels to it during bypass surgery; those procedures can break off deposits, which may then travel to the patient's head and block blood flow through small vessels in the brain. Newman said newer techniques in which the operation is done without the machine, and with little manipulation of the aorta, may help to protect the brain. But not all patients are candidates for the new techniques. In the United States, about 20 percent of bypass operations are done without the heart-lung machine. The machine will always be needed for some cases, Newman said, and for that reason researchers are trying to develop drugs that patients can be given during surgery to help their brain cells tolerate the declines in blood pressure and oxygen level that cannot always be avoided. But other researchers say that it is by no means clear that the heart-lung machine should take all the blame. Dr. Ola A. Selnes, a neuropsychologist at Johns Hopkins, who wrote an editorial in the edition of the journal that includes Newman's study, said other studies had shown cognitive declines in elderly patients who had opera-tions not involving the heart; the stress of anesthesia and surgery may have been too much for them.
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