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Death rates decline following coronary bypass surgery regardless of hospital volume

April 22, 2008

Rates of death following coronary artery bypass graft (CABG) surgery have declined since 1997 while the number of procedures performed has decreased, according to a report in the April issue of Archives of Surgery, one of the JAMA/Archives journals. This suggests that the volume of CABG procedures performed at a given facility may not be a reliable predictor of how patients will fare following the surgery.

"The relationship between increased hospital CABG volume and lower mortality has been consistently observed in the clinical literature," the authors write as background information in the article. "The robustness of this association has led some investigators to suggest that postsurgical morbidity [illness] and mortality [death] could be reduced substantially if hospitals with little working experience in cardiac techniques stopped performing procedures such as CABG."

Rocco Ricciardi, M.D., M.P.H., then of the University of Minnesota, Minneapolis, and now of Lahey Clinic, Tufts University, Burlington, Mass., and colleagues analyzed hospital discharge data from a random sample of 108,087,386 patients admitted to U.S. hospitals between 1988 and 2003. A total of 1,082,218 (1 percent) underwent CABG, while 186,483 received heart valve replacement and repair and 1,589,942 received percutaneous transluminal coronary intervention, another procedure used to treat coronary artery disease. "During our 16-year study period, the rate of CABG increased from 7.2 cases per 1,000 discharges in 1988 to 12.2 cases in 1997 but then decreased to 9.1 cases in 2003, while the rate of percutaneous interventions tripled," the authors write.

"For CABG, the proportion of high-volume hospitals declined from 32.5 percent in 1997 to 15.5 percent in 2003," they continue. Despite this shift, the in-hospital death rate following CABG decreased from 5.4 percent in 1988 to 3.3 percent in 2003. Hospitals performing the fewest CABG procedures experienced the largest decreases in death rates.

The findings suggest that improved quality practices may have disseminated to all facilities performing CABG, the authors note. In addition, lower death rates may have remained constant at previously high-volume hospitals that began performing fewer CABG procedures.

"Our data indicate that in-hospital mortality rates and, possibly, quality care practices are improving everywhere independent of CABG volume," the authors write. "This finding should challenge the setting of any arbitrary volume cut point: positive effects on patient outcome are multifactorial and are inadequately described by procedure volume. In addition, the in-hospital mortality rate after CABG may have diminished to such low levels that it is no longer a useful marker of quality."

JAMA and Archives Journals