For decades, bypass surgery, in which surgeons improve blood flow to the heart by sewing new blood vessels to get around blocked ones, was done the same way.

The heart was stopped while blood was pumped through a heart-lung machine to do the heart’s work. But doctors increasingly worried that the machine, the “pump,” might sometimes lead to strokes or memory problems or personality changes.

In the last seven years, many surgeons began offering and patients increasingly demanded an alternative: off-pump surgery in which the machine was not used and doctors operated on a still-beating heart. Now, a large and rigorous study finds the old way is best.

In the study, published in the New England Journal of Medicine, 2,203 patients were randomly assigned to have their bypass surgery on pump or off.

A year later, it was found that those who had had off-pump surgery had poorer outcomes. Fewer bypasses stayed open and patients were more likely to have needed a repeat operation or to have had a heart attack or to have died. They were no less likely to have had strokes or difficulty thinking.

“This is a big one,” said Dr Eric Peterson, a Duke cardiologist who wrote an editorial accompanying the paper. “It’s a good study and the fact that it did not find superiority was key,” he added. He, like many cardiologists, expectsoff-pump procedures to be superior.

Dr Michael Lauer, director of cardiovascular sciences at the US National Heart, Lung and Blood Institute, said he anticipated and hoped that the new study would dampen enthusiasm for off-pump surgery. “Bypass surgery is one of the most common operations in the world,” Lauer said. “But increasingly, bypasses are being done without the pump. So, this affects a lot of people.”

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