Pennsylvania's Guide to Coronary Artery Bypass Graft (CABG) Surgery 2000 - Understanding the Report

What is Coronary Artery Bypass Graft Surgery?

Coronary artery bypass graft (CABG) surgery is a surgical procedure used to treat patients with blockages in the coronary arteries. During the procedure, a surgeon creates an alternate path for blood to flow to the heart muscle by going around, or bypassing, a blocked section of an artery. CABG (pronounced "cabbage") is invasive surgery that is typically recommended for severe blockages that are not treatable by other methods. The surgeon gains access to the heart by cutting the sternum (breast bone). Blood vessels are removed from the patient's leg or detached from the chest wall and "grafted" to the blocked artery. Once the grafts have been attached, blood will flow through the new bypass vessel, avoiding the blockage completely.

CABG is performed by a cardiothoracic surgeon under general anesthesia and generally takes between two and six hours depending on the number of bypasses to be completed (patients might have more than one blockage, so several bypasses may be needed). After the procedure is completed, most patients stay in the hospital for several days and face a rehabilitation period of about one to two months.

Why is it important to look at CABG surgery?

CABG surgery is a frequently performed and costly surgery. Each year, over 20,000 CABG surgeries are performed in Pennsylvania hospitals at an average charge of approximately $60,000.

While most CABG patients have an excellent prognosis for survival, results following surgery may vary among hospitals and surgeons, so it is important to monitor the performance of Pennsylvania hospitals and surgeons who perform CABG surgery. There is evidence that the information contained in reports such as this encourages hospitals and surgeons to examine their processes and make changes that can improve quality of care and, ultimately, save lives.

New measures in this report

Several new measures are being included in this report for the first time. These measures include 30-day mortality and 7-day and 30-day readmission rates. As with the first time any new measures are examined, the information should be viewed with caution. In addition, readers are also cautioned that the ability to predict events decreases over time and should be considered when examining measures that deal with outcomes up to 30 days after CABG surgery. Finally, while these new measures may provide valuable information, it is important to recognize that this report was an initial attempt to report these new measures and that the risk-adjustment methodology will continue to be reviewed.

PHC4's Technical Advisory Group includes a variety of experts in areas such as medicine, statistics, and health economics. As is customary, the Technical Advisory Group was consulted for this report and in-depth discussions were held on including, in particular, 30-day mortality and 30-day readmission information in this report. While the majority of Technical Advisory Group members voted favorably on the inclusion of these measures, there were dissenting opinions. It should, therefore, be understood that the inclusion of 30-day mortality and 30-day readmission rates represented the majority, and not unanimous, vote of the Technical Advisory Group. These measures are discussed further on page 6.

What is measured in this report and why are these measures important?

This report includes information on the number of surgeries performed, mortality (death) rates during the hospital stay or within 30-days following the surgery, readmission rates within 7 or 30 days, and data on post-surgical lengths of stay. This information is reported for the 55 hospitals and 182 surgeons who performed CABG surgery on adult patients in 2000. In addition, average charge is reported for hospitals. These measures were chosen because they are important components in examining quality of care. Further, they can be reliably measured and compared across hospitals. Other quality of care measures, such as complications following surgery, are important as well but are more difficult to evaluate.

Number of cases

This is the number of CABG surgeries analyzed in this report. This figure gives an idea of the experience the hospitals and surgeons have in treating CABG patients. It is important to note, however, that some CABG patients were not counted in this analysis (for example, those that underwent other complex procedures during the same hospital admission as the CABG surgery), so the actual number of cases that a hospital or surgeon treated might be higher.

In-hospital mortality

This measure represents the number of patients who died during the hospital stay in which the CABG surgery was performed.

30-day mortality

This measure represents the number of patients who died within 30 days of the date of their CABG surgery regardless of "where" the patient died. This measure is important because it includes, for example, those patients who may have been discharged from the hospital but died after returning home.

7-day and 30-day hospital readmissions

Some patients are discharged from the hospital following CABG surgery and are then readmitted at a later date. For this analysis, readmissions were counted only if the patient was readmitted for particular reasons (as indicated by the principal diagnosis of the patient during the readmission; examples include infections, other heart-related conditions, etc.). This report examines how often patients were readmitted to a Pennsylvania hospital within 7 days or 30 days of being discharged from the hospital where the CABG surgery was performed. Readmission rates are important from both a quality of care and cost standpoint. While some readmissions will always occur, high quality care may lessen the need for subsequent hospitalizations.

Information on both 7-day and 30-day readmissions is reported because the reasons for readmission may vary across these time periods. 7-day readmissions account for those readmissions that are closer in time to the initial hospitalization and may be more directly tied to the CABG surgery. At the same time, particular complications may occur after the first 7 days, so adding 30-day readmission rates provides a more completed picture. While much of the scientific literature has focused primarily on 30-day readmission rates, readmissions this far away from the discharge may or may not reflect the care a patient received during the CABG surgery (e.g., a health complication unrelated to the surgery could have developed within the 30 days and necessitated hospitalization).

Post-surgical length of stay

This measure represents how long a patient stayed in the hospital after undergoing CABG surgery. How long a patient stays in the hospital may reflect upon the success of the treatment. While complications following surgery were not examined for this report, other analysis has shown that complications following CABG surgery add to the length of time a patient stays in the hospital. At the same time, it is important to note that various approaches to CABG surgery might affect length of stay. For example hospitals that perform an "off-pump" approach to CABG surgery might have different lengths of stay than the hospitals that do not use this approach. Length of stay is reported in average days instead of a statistical rating that indicates whether the length of stay was significantly longer or shorter than expected. Unlike other measures (such as mortality where a lower number of deaths is obviously better than a higher number), it is not known whether shorter lengths of stay are better than longer lengths of stay or vice versa. Reporting the average length of stay in days, therefore, presents information that can be used to examine differences in lengths of stay without taking a position on what is "best."

Hospital charges

The amount a hospital bills for a patient's care is known as the charge. The charges do not include professional fees (e.g., physician fees) or other additional post-discharge costs, such as rehabilitation treatment, long term care and/or home health care. Hospitals generally do not receive full reimbursement of their charges because insurance companies or other large purchasers of health care services generally negotiate discounts with hospitals. The amount collected by the hospital, therefore, may differ substantially from the charge. Hospital charges often vary by regions of the state. Despite their limitations, charges are a commonly reported surrogate for health care costs.

Uses of the report

This report can be used as a tool to examine hospital and surgeon performance for CABG surgery. It is not intended to be a sole source of information in making decisions about CABG surgery, nor should it be used to generalize about the overall quality of care provided by a hospital or a surgeon. Readers of this report should use it in discussions with their physicians who can answer specific questions and concerns about CABG surgery.

Where does the data come from?

Pennsylvania hospitals are required by law to submit certain information to PHC4. The data used for this analysis was submitted to PHC4 by hospitals in Pennsylvania that perform CABG surgery. It encompasses inpatient hospital discharges from January 1, 2000 to December 31, 2000 in which the patient underwent CABG surgery. The data was subject to verification processes by PHC4 and was verified for accuracy by hospitals and surgeons. In addition, hospitals are required to submit data indicating in simple terms "how sick the patient was on admission." This information is used to make sure that differences in the illness level of patients are accounted for when reporting information on CABG surgery.

Accounting for high-risk patients

Some patients who undergo CABG surgery are more seriously ill than others. In order to report fair comparisons among hospitals and surgeons, PHC4 developed a complex mathematical formula to "risk-adjust" the data, meaning that hospitals and surgeons receive "extra credit" for operating on patients that are more seriously ill or at a greater risk than others. Risk-adjusting the data is important because sicker patients might be more likely to die following CABG surgery, be readmitted, or stay in the hospital longer. A comprehensive description of how these adjustments are made can be found in the Research Methods and Results document that accompanies this report. It can be found on PHC4's website at

What do the symbols mean?

The symbols in this report represent the "bottom line" results of hospitals and surgeons who performed CABG surgery. A statistical test is done to determine whether differences in the results are simply due to chance or random variation. A difference is called "statistically significant" when we are 95 percent confident that the difference is not likely to result from chance or random variation. Using in-hospital mortality as an example:

lower than expected (meaning that the hospital or surgeon had fewer deaths than expected after accounting for how sick the patients were in that hospital)

same as expected (meaning that the hospital or surgeon had as many deaths as expected after accounting for how sick the patients were in that hospital)

higher than expected (meaning that the hospital or surgeon had more deaths than expected after accounting for how sick the patients were in that hospital)