Preliminary results of an international study show that coronary bypass surgery produces subtle, long-lasting impairment of mental performance in nearly one in five people who undergo the operation, researchers say. While the scientists say the problem is not seriously debilitating, patients often report trouble concentrating, remembering new information and performing mental tasks as quickly as they could before their operations.
The study found that the trouble persisted in 17 percent of the patients a year after surgery.
The study is also finding that up to 20 percent of bypass patients are depressed one year after their operations and that their mood change stemmed from damage sustained in surgery.
Some patients suffer both depression and mental difficulties. Yet others become depressed for purely psychological reasons, which are not directly associated with the surgery.
The preliminary findings are far from definitive and their significance is not yet certain. The study has thus far enrolled about 600 patients but has followed only about 150 of them, all in Europe, for a year after their surgery.
The design of the study has been questioned by some experts. And the results seem to contradict dozens of other studies that have looked for subtle brain damage without finding any long-lasting effects.
But the researchers conducting the study say that it identifies a problem that escaped the methods used in earlier studies.
Some American heart surgeons have expressed skepticism that the findings will hold up, and many say that physicians and patients should not be unduly alarmed by the findings because the effects on mental performance, if real, are minor.
But the new study has been praised by some European specialists who believe that bypass operations may indeed be causing subtle brain damage that was not previously recognized.
Experts believe surgeons should be made aware of the risk so safer procedures can be devised and patients should be made aware of the risk so that they can take it into account when deciding with their doctors whether to undergo bypass surgery.
In the procedure, which is performed on about 350,000 Americans a year, a surgeon removes a section of a vein or artery from another part of the body and sews it in position to bypass the blocked artery.
The new research has not determined what causes the mental impairment associated with the procedure, but researchers say that various aspects of the bypass procedure could produce the subtle mental impairments.
For example, blood filters used in heart-lung machines that take over the function of the heart and lungs during the surgery might promote the formation of tiny clots that can plug arteries in the brain and destroy brain cells if they are deprived of oxygen for more than 15 minutes.
Subtle mental impairment "is something you can measure, but I don't know whether to attribute any importance to it," said Dr. Joseph G. Reves, the director of the Heart Center at Duke University Medical Center in Durham, N.C.
Most patients who experience the problem, he said, "are back at work, happy and adjusted," and he added that "the benefits of surgery so clearly outweigh this trivial risk" that patients should not worry about it.