IS BODY-SIZE THE CAUSE FOR POOR OUTCOMES OF CORONARY-ARTERY BYPASS OPERATIONS IN WOMEN

Although small body size and coronary artery diameter are recognized a s major contributors to the increased risk of coronary artery bypass g rafting in women, few studies have established the independent influen ce of body size and gender on outcome. We studied 7025 consecutive pat ients (5694 men, 1331 women) undergoing isolated coronary artery bypas s grafting between 1990 and 1991. Women were older, had higher preoper ative prevalences of urgent operation because of unstable angina, diab etes, peripheral vascular disease, hypertension, and single-vessel cor onary artery disease (p < 0.0001), and a lower prevalence of left vent ricular ejection fraction 40% or less (p < 0.0001). The prevalences of operative mortality (men, 1.8%; women, 3.5%), low-output syndrome (me n, 6.6%; women, 14.8%), and myocardial infarction (men, 2.8%; women, 5 .5%) were higher in women (p < 0.0001). Patients were divided into qua rtiles for body surface area, weight, height, and body mass index. For both men and women, there was no difference in operative mortality be tween the highest and lowest quartiles of body size. Women, however, h ad a higher prevalence of operative mortality than men in the lower qu artiles of body surface area, height, and weight and in the higher qua rtiles of body mass index. Among men, the prevalence of low-output syn drome increased (p < 0.0001) with decreasing body surface area, weight , and body mass index, suggesting that body size did influence the pre valence of low-output syndrome. However, women had a higher prevalence of low-output syndrome than men in every category and quartile of bod y size (p < 0.0001). Multivariable analysis identified gender as a sig nificant determinant of operative mortality (odds ratio 1.83, 95% conf idence interval 1.27 to 2.64) and low-output syndrome (odds ratio 2.52 , 95% confidence interval 2.05 to 3.11). When multivariable adjustment s were made for body size and preoperative risk factors, gender remain ed a predictor of both operative mortality and low-output syndrome. Mu ltivariable assessment of risk for men and women separately identified that urgent operation was a predictor of operative mortality (odds ra tio 2.52, 95% confidence interval 1.32 to 5.61) and low-output syndrom e (odds ratio 1.57, 95% confidence interval 1.14 to 2.17) in women but not men. In conclusion, the increased risk of coronary artery bypass grafting in women may be explained in part by dramatic differences in preoperative risk factors between men and women. In both men and women , small body size did not increase the risk of operative mortality, bu t may have contributed to the risk of low-output syndrome. After adjus ting for preoperative risk variables and body size, gender remains a s ignificant independent predictor of operative mortality and low-output syndrome.