Smaller body size is a major reason why women have a higher risk of dying after coronary artery bypass graft surgery than men do, according to an article in the August 30 issue of Circulation.

“Women undergoing bypass surgery have a death rate about twice as high as men,” said Ron Blankstein, MD, author of the study and a cardiology fellow at the University of Chicago Hospitals. “Our study shows that a significant degree of their higher mortality may be due to the fact that women generally have smaller bodies.”

Smaller bodies mean smaller coronary arteries that may be technically more difficult on which to operate, he explained. However, even after considering smaller body size and known risk factors for poor outcomes during surgery, such as older age, hypertension, and diabetes, women were still more likely to die after bypass graft surgery than men.

“The worse outcomes among women should not keep them from having surgery,” he said. “For many patients, coronary artery bypass grafting still represents the optimal therapy for their coronary heart disease.”

Researchers reviewed data on 15,440 patients (5,023 women) who underwent surgery at 31 midwestern US hospitals in 1999-2000. Average age for women was 66 years compared with 63 years for men.

Overall, 4.2 percent of women and 2.2 percent of men died during or immediately after surgery, a 90 percent higher death rate for women than men. Nearly half of the excess mortality may be because women were often older and sicker at the time of the surgery than the men, Blankstein said.

Statistical analyses that considered other risk factors, more severe disease, and the presence of other health conditions, reduced the gender gap in death rates from 90 percent to 49 percent.

The gender gap was reduced even further when researchers considered body surface area (BSA). BSA is a measure of body size based on a person’s height and weight. When controlled for women’s lower average BSA, a large part of women’s higher death rate was explained. As a result, the “gender gap” in death risk was reduced from 49 percent to 22 percent.

“Our study shows that body surface area, or body size, is a very important independent predictor for mortality on top of all the other risk factors,” Blankstein said.

After accounting for lower body surface area and other risk factors, why are women still 22 percent more likely to die after bypass graft surgery than men are? That is a critical question for future research, Blankstein said. Potential factors to explore are differences in body fat composition, which may make tissues and blood vessels less likely to heal, and the role of hormones, particularly in postmenopausal women.