The best bypass surgery choice may be to use a heart–lung machine, after all, according to a new study published Thursday in The New England Journal of Medicine.

Surprising many in the field, off-pump surgery did not win out in a large comparison study—and actually resulted in patients who were slightly more likely to need additional operations or to have heart attacks.

Some patients who have had open-heart surgery while hooked up to a heart–lung machine have complained of a cognitive cloudiness that set in after their procedure. The machine, also called a cardiopulmonary-bypass pump, keeps the blood circulating and oxygenated while the heart is stopped for the operation, but some have worried that it can have long-term effects on the brain.

In an effort to avoid post-op "pumphead," many doctors and patients had been opting for off-pump surgery that allowed the heart to keep beating during the operation. And each year, some 20 percent of the quarter-of-a-million bypass patients have off-pump surgery, The New York Times noted.

In the U.S. Department of Veterans Affairs-sponsored study, 2,203 cardiac patients were randomly assigned to either on- or off-pump bypass surgery. After medical monitoring and follow-up, the researchers found no difference in the neuropsychological states of patients, and even that, "patients in the off-pump group had worse composite outcomes…than did patients in the on-pump group," the authors wrote.

"For the vast majority [of patients], there's no advantage to doing it off-pump and there may be some disadvantages," Frederick Grover, a professor of surgery at the University of Colorado in Denver, and study co-author, told the Associated Press.

"This is a big one," Eric Peterson, a cardiologist from Duke University who wrote a commentary that ran with the study, told the Times. "It's a good study, and the fact that it did not find superiority was key."

Some heart surgeons who specialize in off-pump surgery will continue to stand by the procedure, the Times reported. The technique "will probably remain a technique reserved for selected patients and skilled surgeon advocates," Peterson wrote in his editorial.

In 2001, a study of 261 on-pump heart disease patients (also published in The New England Journal of Medicine) showed that 42 percent later showed cognitive decline. But other researchers complained that the study had neglected to include a control group for comparison. A six-year study published in August in The Annals of Thoracic Surgery followed 395 people, some of whom had coronary disease and other who didn't, who underwent on- or off-pump surgery or non-surgical intervention. The researchers found that in fact it was heart disease—not the type of surgery—that determined whether cognitive slipping was more likely.

"I would find myself hard pressed to justify it for someone who is at moderate or somewhat-high risk," Grover told Reuters about off-pump surgery. "I don't think the trade-off is worth it myself."

In his editorial, however, Peterson noted that despite the study's size and surprising findings, it "is unlikely to end the debate about off-pump and on-pump" bypass surgery.

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