Hospital volume may not be best criteria for selecting hospital for coronary bypass surgery

January 13, 2004

For coronary artery bypass graft surgery (CABG), hospital procedural volume is only modestly associated with outcomes and therefore may not be an adequate quality indicator, according to a study in the January 14 issue of The Journal of the American Medical Association (JAMA).

There have been recent calls for using hospital procedural volume as a quality indictor for CABG surgery, but further research into analysis and policy implication is needed before hospital procedural volume is accepted as a standard quality measure, according to background information in the article.

Eric D. Peterson, M.D., M.P.H., of the Duke Clinical Research Institute, Durham, N.C., and colleagues examined the association between hospital CABG procedural volume and outcome using clinical data available from the Society of Thoracic Surgeons (STS) National Cardiac Database. The analysis included 267,089 CABG procedures performed at 439 U.S. hospitals between January 1, 2000, and December 31, 2001.

The researchers found that the median (interquartile range) annual hospital volume for isolated CABG procedures was 253 (165-417), with 82 percent of centers performing fewer than 500 procedures per year. The overall operative mortality was 2.66 percent. After adjusting for patient risk and clustering effects, rates of operative mortality decreased with increasing hospital CABG volume (0.07 percent for every 100 additional CABG procedures). "While the association between volume and outcome was statistically significant overall, this association was not observed in patients younger than 65 years or in those at low operative risk and was confounded by surgeon volume. The ability of hospital volume to discriminate those centers with significantly better or worse mortality was limited due to the wide variability in risk-adjusted mortality among hospitals with similar volume. Closure of up to 100 of the lowest-volume centers (i.e., those performing 150 or less CABG procedures/year) was estimated to avert fewer than 50 of 7,110 (less than 1 percent of total) CABG-related deaths," the researchers write.

"Our study [expanded on] prior analyses using contemporary analytic techniques to properly account for clinical factors, differences in site variability, and clustering within sites. We found that, compared with high-volume hospitals, low-volume hospitals tended to operate on patients with higher risk and under more emergent conditions," the author write. "Our study further demonstrates the limitations of using hospital volume as an indicator of the quality of CABG surgery. Hospital volume had generally poor predictive accuracy as a means of identifying hospitals with significantly better or worse CABG mortality rates. Similarly, using volume as a sole referral criterion for selecting a provider would unfairly defer cases from nearly half of very-low-volume centers with outcomes equal or better than overall STS mortality results."

"In this national study we found that hospital procedural volume was only modestly associated with risk-adjusted CABG mortality rates; however, there were many low-volume hospitals with low mortality rates and some high-volume centers with rates higher than expected. This study suggests that hospital CABG surgery volume is best considered as a surrogate for quality in a setting where other more direct process and outcome assessments are not available. Instead it seems more reasonable to support the continued growth of national clinical databases, which are capable not only of tracking risk-adjusted surgical care patterns and outcomes, but also of improving them," the authors conclude. (JAMA. 2004;291:195-201. Available post-embargo at
Editor's Note: The study was sponsored by the Society of Thoracic Surgeons. Specifically, the Duke Clinical Research Institute has a contract with the STS to be their National Cardiac Data Warehouse and Analysis Center (Dr. Peterson, principal investigator of this subcontract).


In an accompanying editorial, David M. Shahian, M.D., of Lahey Clinic, Burlington, Mass., discusses the issues concerning cardiac surgery and hospital volume.

"A number of methodological, statistical, and conceptual concerns regarding the relationship between volume and outcome remain unresolved. Many investigations have used inadequately adjusted Medicare administrative data, volume thresholds vary substantially among procedures and studies, and the mechanism for the association between volume and outcome remains uncertain. The overall relationship is also confounded by the fact that many low-volume programs have excellent outcomes," he writes.

"The public and the media must be educated as to the limitations of even the most sophisticated risk models, the futility of attempting to rank hospitals, and the fluctuations in outcome that occur naturally from year to year. Consumers, regulators, and insurers would be best advised to study such outcome data longitudinally to identify consistent and egregious outliers."

"Most importantly, the processes that permit some hospitals and surgeons to consistently obtain better results must be identified. The fact that many low-volume hospitals achieve excellent outcomes suggests that superior processes, rather than volume per se, may be an important mechanism for high performance. Perhaps some of these processes are more easily and consistently implemented by high-volume centers, but they are certainly not restricted to them. Efforts to disseminate these best practices to all hospitals and surgeons must intensify, because this is the best way to reduce interprovider variability and to improve the quality of all cardiac surgery programs. Use of processes known to be associated with superior results will become a more widely adopted quality measure, as this approach does not rely on sophisticated yet still imperfect methods of risk adjustment," Dr. Shahian concludes. (JAMA. 2004;291:246-248. Available post-embargo at

Editor's Note: Dr. Shahian is a former member of the Society of Thoracic Surgeons National Database Committee, a current member of the STS Evidence-Based Medicine Workforce, and chair of the STS Task Force on Cardiac Risk Models. He also serves as chair of the Massachusetts Cardiac Care Quality Commission. The views expressed in this editorial do not necessarily reflect the opinion or policies of the STS or any agency of the Commonwealth of Massachusetts.

The JAMA Network Journals

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