Editorial Gender Disparity in CABG Outcomes: An Independent Risk Factor or Not, Women Are at a Disadvantage

In this issue of the Journal, Sharoni E. et al. from Rabin Medical Center evaluate the impact of female gender on postoperative morbidity and mortality after coronary artery bypass grafting (CABG) surgery. The authors retrospectively analyzed 1 758 isolated first-time CABG patients operated from 2003 to 2005 and found that women had distinctly different pre- and intraoperative profiles compared with men, and also a significantly higher postoperative mortality. On propensity scoring of 359 matched pairs, and validation with the bootstrap technique, female gender was not found to be an independent risk factor of death after CABG in their study. This data is based on a single center experience and seems to contradict some of the earlier studies demonstrating that female gender is in itself an independent risk factor for mortality.

Previously published data have shown that women are less likely to undergo percutaneous intervention (PCI) or CABG procedures and there is a question whether this is secondary to the perception that women have a less favorable outcome. Over the years, it appeared that women had a higher morbidity and mortality after PCI or CABG and lower success rates for CABG but they shared similar long-term outcomes to men once peri-procedural risk factors and characteristics were accounted for. To date, the controversy still exists about whether differences in clinical outcomes can be attributed to female gender itself or to other associated unfavorable characteristics or factors.

In the majority of the previously published studies women who underwent CABG needed more urgent or emergent operations and had a higher incidence of perioperative myocardial infarction (MI), congestive heart failure (CHF) and anemia. Women undergoing CABG were also older, had a lower body surface area (BSA), and a higher incidence of diabetes, obesity, and hypertension. These associated comorbidities are known to contribute to a significantly higher perioperative mortality following CABG.

From the studies that looked at the rate of perioperative MI following CABG, it appears that the higher incidence of emergent CABG in women is secondary to more acute and unstable disease. This is supported by more recent studies suggesting that, once women present with an acute MI or once they undergo cardiac catheterization, their revascularization rate is not any different from that of their male counterparts. Furthermore, their left ventricular ejection fraction is not adversely affected by the increased urgency at presentation. Other studies have concluded that lower BSA by itself is an independent risk factor for increased mortality regardless of gender.

Women generally receive fewer arterial grafts and less extensive revascularization and this has been demonstrated by many single center series in which bias in decision-making was eliminated or accounted for. This was also reproduced through database analysis and was partly explained by the difference in age between the two sexes and the greater need for emergent CABG among women. It is well known that the use of arterial conduits in itself affects both short- and long-term survival regardless of gender.

Women are more likely to require postoperative inotropic support, more intra-aortic balloon pump (IABP) support and more peri-procedural blood transfusions. They are also more likely to have prolonged hospital stays following CABG. All of these factors have a major influence on the peri-procedural morbidity and complication rate following CABG and may account for the higher incidence of complications in women. Whereas some multivariate regression analysis studies have demonstrated female gender to be an independent risk factor for mortality following CABG, other similar studies using regression analysis have shown that female gender was not an independent predictor of postoperative complications or death, suggesting that these outcomes are associated with co-morbid conditions, which are more prevalent among women than among men.

A limitation of the published study presented in this issue is that it is of an observational retrospective nature from a part of the world where referral patterns for CABG among men and women may be different from that in Western Europe or North America. Another limitation that was also acknowledged by the authors is that it was based on a propensity matching model which has its own limitations. If the model did not include certain balancing variables then that could potentially adversely impact the results.

An important point that was stressed by the authors of this present study, and is echoed by other investigators in previous studies, is that propensity modeling has an important advantage over multivariate analysis and regression adjustment in that the investigator may find that there is effectively no overlap in the distribution of covariants between the groups under investigation.

In summary, female gender appears to be a risk factor for mortality and at least short-term morbidity following CABG. Both regression analysis methods of statistical analysis as well as propensity models have been utilized to support or negate the argument on whether this gender difference is, or is not, an independent predictor of death. Regardless of the final verdict of these studies, gender analysis clearly shows that women are at a disadvantage when it comes to CABG outcomes.

Reference

• 1 Sharoni E, Kogan A, Medalion B, Stamler A, Snir E, Porat E. Is gender an independent risk factor for coronary bypass grafting?.  Thorac Cardiovasc Surg. 2009;  57 204-208