Women are nearly twice as likely as men to die from complications of heart bypass surgery, and their typically smaller body size may be one of the reasons, according to a study published Tuesday.

In a review of records for 15,440 patients who had undergone coronary artery bypass grafting (CABG), researchers found that 4.24 percent of women died during or immediately after surgery, versus 2.23 percent of men, a statistically significant difference.

The main reasons for the gender gap were the higher rates of "traditional risk factors" among women, said lead study author Dr. Ron Blankstein. In general, the study found, women were older and more likely than men to have problems such as diabetes and advanced heart failure.

But another factor was body size. Patients with a relatively smaller "body surface area" were at greater risk of dying from heart bypass surgery, and in general, women have smaller bodies than men.

Body surface area is an indication of the size of a person's coronary arteries, and smaller vessels can make the surgery "technically more difficult," explained Blankstein, a cardiology fellow at the University of Chicago Hospitals.

This fact, he and his colleagues speculate, may be why smaller body size was linked to poorer survival.

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.

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