The new findings appear in today's electronic edition of Circulation.
According to the research, women of all ages died more often than their male counterparts; 5.3 percent of women died before leaving the hospital after bypass surgery, compared to 2.9 percent of men. Breaking those numbers down even further, the decade-by-decade results showed the biggest gap in the small but significant group that had the operation before age 50. Here, 3.4 percent of women died, compared to just 1.1 percent of men."It was by far the most dramatic difference between the genders," says lead study author Dr. Viola Vaccarino, associate professor of medicine at Emory University in Atlanta, where the research took place.
While Vaccarino says the gap between the genders closed a bit over the next two decades of life, another significant spread occurred in those having the operation between the ages of 70 and 79.
"The differences between death rates among the sexes didn't level off again until we looked at operations performed on people in their 80s," Vaccarino says.
Bypass surgery uses snippets of blood vessels taken from various parts of the body to replace sections of damaged or clogged vessels leading to the heart. The goal is to increase blood flow and oxygen. Some 600,000 bypass surgeries are performed in the United States each year, with nearly 200,000 done on women, the American Heart Association says.
Vaccarino isn't clear why the gender difference exists. However, the study did show a higher rate of diabetes and kidney disease among the women in the study, particularly the younger women.
She notes that while women in the study may have had more pre-existing illnesses and risk factors in their medical history, they generally had less heart disease and stronger hearts overall, with fewer heart attacks than men before surgery.
Additionally, when all disease factors were figured into the study calculations, they accounted for less than a 30 percent difference in mortality rates between men and women.
So, what could be causing the gap between the sexes? While Vaccarino says she has no proof, she suspects estrogen may play a role.
While Vaccarino says it's only a theory, there is some evidence to indicate that estrogen could be acting as a kind of inflammatory agent that in some way disrupts the success of the bypass surgery
While early research has indicated this might be the case with synthetic estrogen, Vaccarino admits there is no such proof that natural estrogen -- thought to protect women from heart disease -- could have any detrimental effects on bypass surgery.
Still, she says, "it's a provocative theory we might want to explore further."
The current study examined the medical records of nearly 52,000 patients in the National Cardiovascular Network, a database of women and men who underwent bypass surgery at 23 medical centers around the United States between October 1993 and December 1999.
Of these patients, 15,178 -- or 29.7 percent -- were women. There were fewer white women than white men and, on average, the women were older -- 67.5 years old compared to 64.1 years for men.
Researchers grouped the patients into the following five age categories: under 50, 50 to 59, 60 to 69, 70 to 79, and 80 and older. The doctors then factored out general health characteristics, illnesses other than heart disease, and heart disease risk factors, such as too much weight or smoking.
In the 50-to-59 age group, 2.6 percent of women died, compared to 1.1 percent of men. In the 60-to-69 age group, 3.6 percent of women died, compared to 2.6 percent of men, showing the gap was starting to close.
"But by the time we got to the 70-to-79 age group, the gap widened again," Vaccarino says.
Numbers did not come together again until both groups reached their 80s, when 9 percent of women died, compared to 8.3 percent of men.
Dr. Nieca Goldberg, director of the Women's Heart Center at Lenox Hill Hospital in New York City, says the Emory study is sound, and has significance that reaches far beyond what the data tells us.
"What this study is also saying is that women are not small men, and what we have learned about treating heart disease by treating men, we cannot automatically apply to women. There are differences between the genders that must be addressed," Goldberg says.
Cardiologists must take the initiative to learn more about the physiological differences between women and men to prevent the differences in death rates, Goldberg says.
What To Do
To learn more about women and heart disease, visit The American Heart Association or the The National Coalition For Women With Heart Disease.
To discover the rate of heart disease for women in your state, check the Centers for Disease Control and Prevention.
To learn more about bypass surgery, visit The University of Southern California Keck School of Medicine.