Coronary bypass surgery death rates decline, regardless of hospital volume

Coronary bypass surgery death rates decline, regardless of hospital volume

Since 1997, rates of death subsequent to coronary artery bypass graft (CABG) surgery have been dropping, while the number of procedures performed has decreased, according to an article released on April 21, 2008 in Archives of Surgery, a JAMA/Archives journal. This indicates that the volume of CABG procedures that are conducted in a given facility may not be an accurate predictor of patients' health after the surgery.

The authors note that this has not always been observed. In fact, they state that "The relationship between increased hospital CABG volume and lower mortality has been consistently observed in the clinical literature." This has in turn led to certain attitudes about how CABG procedures should be organized: "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."

In order to investigate this, 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 examined the hospital discharge records from a random sample of more than 108,087,386 patients admitted to United States hospitals between the years of 1988 and 2003. A total 1,082,218 of these (1%) underwent CABG surgery, 186,483 received heart valve replacement and repair. and 1,589,942 received percutaneous transluminal coronary intervention (another procedure often used to treat coronary artery disease.)

The authors write that CABG procedures fluctuated in proportion over time. "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."Additionally, the distribution of these surgeries in different hospitals changed. "For CABG, the proportion of high-volume hospitals declined from 32.5 percent in 1997 to 15.5 percent in 2003."

These findings indicate that the quality of practice may have improved over time in all facilities performing CABG. Lower death rates may have remained constant at the previously high volume hospitals that subsequently began performing fewer CABG procedures, increasing the mortality rate at these facilities.

The authors conclude with some modifications to the current popular opinion on CABG volume and effectiveness. "Our data indicate that in-hospital mortality rates and, possibly, quality care practices are improving everywhere independent of CABG volume." They continue: "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."

Volume-Outcome Relationship for Coronary Artery Bypass Grafting in an Era of Decreasing Volume

Rocco Ricciardi; Beth A. Virnig; James W. Ogilvie Jr; Peter S. Dahlberg; Harry P. Selker; Nancy N. Baxter

Arch Surg. 2008;143(4):338-344.

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Section Issues On Medicine: Cardiology