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Hospital risk-adjusted mortality rates differ between male, female Medicare beneficiaries undergoing CABG surgery, study reveals

Monday, December 15 2008 | Comments

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What's This? The male and female differences that exist in hospital risk-adjusted mortality rates for Medicare beneficiaries undergoing coronary artery bypass graft (CABG) surgery increase from top- to bottom-tier hospitals, suggesting that female beneficiaries could benefit from having CABG performed at tier 1 hospitals, according to recent data.

"[T]he growing awareness of sex differences in cardiovascular outcomes has raised concerns about whether the sex differential in risk-adjusted mortality rate varies across hospital performance tiers," the study researchers wrote.

In their retrospective analysis, the research team ranked U.S. hospitals that performed CABG surgery on Medicare beneficiaries into 4 performance tiers and determined whether there were overall and sex-specific differences in the risk-adjusted mortality rates across performance tiers. Each hospital had to be outside of the Veterans Affairs Hospital System and had to have performed at least 52 CABG procedures without concomitant valve surgery on Medicare beneficiaries during fiscal years 2003 or 2004.

Each hospital's CABG surgery performance was based on the potential number of lives saved, which was defined as the difference between the hospital's expected number of deaths and its observed number of deaths.

The final study population consisted of 134,407 Medicare beneficiaries and 802 hospitals in fiscal year 2003 and 122,231 Medicare beneficiaries and 768 hospitals in fiscal year 2004.

The number of estimated lives saved in the study hospitals ranged from +15.91 to -21.86 during FY2003 and from +15.06 to -15.82 during FY2004.

As anticipated, the estimated number of lives saved declined from tier 1 to tier 4; however, the researchers noted that the average CABG volume per hospital per year was higher in tier 1 and tier 4 than in the middle 2 tiers. The data revealed a slight decrease in the average hospital observed mortality rate (3.72% vs 3.63%) and risk-adjusted mortality rate (3.68% vs 3.61%) among Medicare beneficiaries undergoing CABG surgery from FY2003 to FY2004.

Furthermore, male beneficiaries had lower observed mortality rates than female beneficiaries (3.7% vs 4.8% in FY2003 and 3.1% vs 4.7% in FY2004). Risk-adjusted mortality rates were also lower among men (3.2% vs 4.7% in FY2003 and 3.1% vs 4.7% in FY2004).

In 2004, the average risk-adjusted mortality rate ranged from 1.39% in tier 1 hospitals to 6.40% in tier 4 hospitals. The sex-specific mortality rate was consistently higher for women in all tiers, with the differential smallest (0.68%) in tier 1 hospitals and greatest (2.67%) in tier 4 hospitals.

"[T]his study provides evidence that Medicare beneficiaries should pay attention to hospital performance rankings for CABG surgery based on lives saved. We also suggest that improving the quality of care in poorer-performing hospitals may be an important opportunity for improving CABG surgery outcomes," the authors concluded.

Furthermore, they said, "The sex differential is smallest at high-performing hospitals meaning that both male and female beneficiaries benefit from having CABG performed at tier 1 hospitals. Future research is needed to focus on the processes and structures that differentiate the top performers and how these lessons can be translated to other hospitals." (Culler S, et al. Arch Intern Med 2008;168:2317-2322.)

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