However, body size and traditional risk factors did not fully explain the higher death risk among female patients, Blankstein told Reuters Health.
"Just being female is itself a risk factor," he said. "We need to figure out why this is."
Blankstein and his colleagues report their findings in the annual Cardiovascular Surgery Supplement of Circulation, a journal published by the American Heart Association.
During CABG, a surgeon takes blood vessels from a patient's leg or elsewhere in the body and uses them to reroute blood around a blockage in the arteries that normally supply the heart. Though coronary artery disease can often be managed with drug therapy or angioplasty —— a less invasive procedure that opens up clogged arteries —— some patients require CABG.
Blankstein said that while the new findings are "sobering," they should not discourage women from having the surgery if they need it.
"For a lot of women," he noted, "bypass still represents the best option for their disease."
The study involved patients who underwent CABG at one of 31 hospitals in the Midwestern U.S. in 1999 and 2000. Overall, women were 90 percent more likely than men to die during or soon after surgery.
When the researchers accounted for a variety of potential risk factors, including age, co-existing diseases and body size, the gender gap narrowed substantially. Still, women remained 22 percent more likely to die compared with men.
It will be important to find out why this discrepancy persists even when standard risk factors are considered, Blankstein said.
Some open questions, according to the researchers, are whether body fat plays a role, since it affects healing in tissues and blood vessels, and whether hormonal differences between women and men could be at work.