Related Experiment Video
Updated: Jul 8, 2026
Surgical Swine Model of Chronic Cardiac Ischemia Treated by Off-Pump Coronary Artery Bypass Graft Surgery
Published on: March 27, 2018
The CABG surgery volume-outcome relationship: temporal trends and selection effects in California, 1998-2004
James P Marcin1, Zhongmin Li, Richard L Kravitz
1Department of Pediatrics, UC Davis Children's Hospital, and Center for Health Services Research in Primary Care, 2516 Stockton Boulevard, Sacramento, CA 95817, USA.
Insights
A weak link between hospital volume and outcomes for coronary artery bypass graft (CABG) surgery in California disappeared after mandatory reporting began. This suggests mandatory reporting may obscure the volume-outcome relationship in CABG surgery.
Area of Science:
- Health Services Research
- Surgical Outcomes
- Health Policy Analysis
Background:
- The relationship between hospital volume and patient outcomes is a key consideration in healthcare quality assessment.
- Understanding temporal trends and the impact of reporting mandates on this relationship is crucial for effective policy development.
Purpose of the Study:
- To examine the evolution of the volume-outcome relationship for coronary artery bypass graft (CABG) surgery in California between 1998 and 2004.
- To evaluate how voluntary versus mandatory hospital reporting systems influenced this relationship.
Main Methods:
- Utilized patient-level clinical data from California's voluntary (1998-2002) and mandatory (2003-2004) CABG reporting programs.
- Employed hierarchical logistic regression to analyze the association between hospital annual volume and in-hospital mortality, controlling for patient covariates.
Main Results:
- A significant inverse volume-outcome relationship for CABG surgery was observed during the voluntary reporting period (1998-2002), with higher volume hospitals showing lower mortality.
- This association vanished during the mandatory reporting period (2003-2004).
- The absence of the relationship in later years was not attributable to reporting bias from newly included hospitals.
Conclusions:
- The volume-outcome relationship in California CABG surgery weakened and subsequently disappeared with the transition to mandatory reporting.
- The implementation of a mandatory statewide reporting program coincided with the loss of this association, highlighting potential impacts on quality monitoring.
Objective:
To investigate the temporal trends in the volume-outcome relationship in coronary artery bypass graft (CABG) surgery in California from 1998 to 2004, and to assess the selection effects on this relationship by using data from periods of voluntary and mandatory hospital reporting.
Data Sources:
We used patient-level clinical data collected for the California CABG Mortality Reporting Program (CCMRP, a voluntary reporting program with between 68 and 81 hospitals) from 1998 to 2002 and the California CABG Outcomes Reporting Program (CCORP, a mandatory reporting program with 121 and 120 hospitals) from 2003 to 2004.
Study Design:
The patient was the primary unit of analysis, and in-hospital mortality was the primary outcome. We used hierarchical logistic regression models (generalized linear mixed models) to assess the association of hospital annual volume with hospital mortality while controlling for detailed patient-level covariates in each of the 7 years.
Data Collection Methods:
All data were systematically collected, reviewed for accuracy, and validated by the State of California's Office of Statewide Health Planning and Development (OSHPD).
Principal Findings:
We found that during the period of voluntary hospital reporting (1998-2002), with the exception of 1998, higher volume hospitals had significantly lower risk-adjusted in-hospital mortality rates, on average, than lower volume hospitals (1998 odds ratio [OR] per 100 operations performed = 0.962, 95 percent confidence interval [CI]: 0.912-1.015; 1999 OR=0.955, 95 percent CI: 0.920-0.991; 2000 OR=0.942, 95 percent CI: 0.897-0.989; 2001 OR=0.935, 95 percent CI: 0.887-0.986; 2002 OR=0.946, 95 percent CI: 0.899-0.997). We also found that in the period of mandatory reporting (2003 and 2004) there was no volume-outcome relationship (2003 OR=0.997, 95 percent CI: 0.939-1.058; 2004 OR=0.984, 95 percent CI: 0.915-1.058) and that this lack of association was not due to a reporting bias from the addition of data from hospitals that did not originally contribute during the voluntary program.
Conclusions:
In California, where no state regulations support regionalization of CABG surgeries, a weak volume-outcome relationship was present from 1998 to 2002, but was absent in 2003 and 2004. The disappearance of the volume-outcome association was temporally related to the implementation of a statewide mandatory CABG surgery reporting program.
