Early initiatives measured the quality of cardiac surgery only by how often patients died. Furthermore, because coronary artery bypass grafting surgery (CABG) is the most common, signature cardiac surgical procedure, CABG mortality served for many years as the sole metric of cardiac surgical performance. A major early contribution of the Database was the development of risk-adjustment techniques. To accurately measure cardiac surgery outcomes, it is essential to adjust the results for each surgeon and hospital by accounting for the severity of their patients’ illnesses, a process commonly known as risk adjustment. Some hospitals care for more seriously ill patients, and such patients are at greater risk of dying because of their underlying conditions, not necessarily because of the care they receive. If there was no way to account for such risks, some excellent surgeons and hospitals would have higher death rates and appear to be providing poor quality care, when in fact they simply have sicker patients. To level the playing field, statistical techniques have been developed to account for the condition of patients before surgery. This has resulted in one of the most commonly reported measures of cardiac surgery quality, the risk-adjusted or risk-standardized mortality rate. STS has developed risk models for CABG, valve, and combined valve and CABG operations that have all received national recognition and endorsement.
There is now an increasing recognition nationally that performance measurement must be more comprehensive than just single procedures and outcomes. For example, consider two patients who survive CABG surgery. One has a perfectly uncomplicated course and receives all the appropriate treatments postoperatively, whereas the other patient develops kidney failure or a serious wound infection. Although both patients are survivors, their quality of care may have been very different. Because of such considerations, many organizations have recommended the use of multiple measures of quality for specific conditions and procedures, sometimes combining them into one number called a composite score. The composite score is a single number or rating that summarizes all available information about the quality of care delivered by an individual provider. It is this principle that led The Society of Thoracic Surgeons to develop what is known as the STS CABG composite score and rating, now one of the most sophisticated and widely regarded overall measures of quality in health care. Subsequently the STS AVR composite score and most recently the STS AVR+CABG composite score were developed due to the success of its CABG predecessor, and further composite measures for other procedures are currently being developed.