DALLAS (AP) - Patients who undergo bypass surgery soon after a heart attack may have an increased risk of stroke - a finding that suggests there may be a price to pay for aggressively treating heart disease, researchers say.

Researchers involved in the study, called the largest of its kind, looked at more than 18,000 patients who had either mild heart attacks or a type of chest pain called unstable angina between 1995 and 1998.

People who had bypass surgery within two weeks of being hospitalized were twice as likely to have a stroke as those who had later bypasses. The early bypass patients were four times more likely to have a stroke than those who did not have surgery at all.

"Doctors may have a valid and important reasons for referring patients for bypass surgery," said Dr. Shamir Mehta, a cardiologist at McMaster University in Hamilton, Ontario, and a study co-author. "We all are adopting a more aggressive approach to the management of these patients, which I think is largely appropriate. Our study simply sends a gentle reminder to physicians that, in certain high-risk patients, there is an increased stroke risk after early bypass surgery."

During bypass surgery, surgeons take a blood vessel from another part of the body, such as the leg, and construct a detour around the blocked part of a heart artery. Stroke as a complication of bypass surgery is considered rare.

Only 238 of the patients, or 1.3 percent, had strokes during a six-month follow-up. But 46 of them, about one-fifth, were fatal.

"There was a marked early increase in strokes during the first month after admission, followed by a lower rate of increase over the next five months" according to the study in Monday's Circulation, a journal of the American Heart Association.

The research did not find an increased stroke risk for patients who underwent procedures such as balloon angioplasty, in which a tiny balloon to is used to unclog a blood vessel.

The patients who had strokes were older and more likely to have higher blood pressure, diabetes and other risk factors.

During bypass surgery, blood clots can form, circulation can be compromised and bleeding can happen. Such factors can contribute to the chance of stroke in heart patients, who already run a higher risk.

Dr. Eric Topol, chairman of cardiology at the Cleveland Clinic, said doctors should be aware of the higher percentage of stroke deaths after an early bypass.

"We need to get that down as close to zero as possible. We need to come up with better ways to prevent that," he said.

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