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Coronary artery bypass surgery, hospital volume, and risk.

To the Editor:

The recent article by Goodney and colleagues1 in Circulation found that differences in 30-day mortality rates between low- and high-volume hospitals were consistent across both low- and high-risk surgical groups, leading the authors to conclude that a policy of targeted regionalization is unlikely to be of value in coronary artery bypass surgery (CABG). On the surface, this finding appears to directly contradict results of an earlier analysis performed by our group, in which we observed that differences in in-hospital mortality rates after CABG may be modified by a patient’s predicted operative risk.2 So how can discrepancies between these 2 studies be resolved?

Although there are indeed several methodological differences between the studies (which Goodney et al1 carefully point out), we believe the authors minimized the most likely explanation for dissimilar results: Dramatically different definitions of low-risk. Specifically, the lowest-risk group in our study–ie, the group in which hospital volume appeared to have no substantial effect–had a predicted operative mortality rate of <0.5%. This is in comparison to a predicted operative mortality rate of 4.3% for the corresponding lowest-risk group in the study by Goodney et al1 (broadly defined as the lower 75th risk percentile). In fact, if one scrutinizes their results, the study by Goodney and colleagues re-confirms one of our key findings; we also noted that hospital volume has an important and consistent effect on patients with predicted …