The results of this study show that the vast majority of the 40,374 isolated CABG surgeries performed during 2003 and 2004 in California were associated with "probable" or "possible" survival enhancing indications. The findings are consistent with data obtained from more detailed clinical studies of the clinical appropriateness of CABG surgery [13
], and are, in the aggregate, reassuring. However, hospitals varied significantly in terms of the severity of CAD selected for bypass surgery. Most CABG operations were for SEIs, but in 32 hospitals (26%), patients lacking a probable SEI constituted at least one-fifth of patients taken to surgery.
We used a hierarchical logistic regression model on hospital characteristics and patient demographics to estimate ICC values, which measures the fraction of variation (residual variance) that is explained by hospital or surgeon or both. We found that these fractions were small for hospital and surgeon, suggesting that patient mix might be more important than hospital and surgeon effects in explaining the variation in use of CABG surgery for SEI. We also found that the ICC value for hospitals was larger than the value for surgeons, suggesting that some elements of cardiac surgical decision making might be related more directly to hospital referral patterns and culture than to the judgment of individual surgeons.
For a number of reasons, the proportion of surgeries performed for "probable SEIs" is not a strong measure of quality or appropriateness at the level of the individual surgeon or hospital, but this metric may still be useful as a window into the critical issue of patient selection. As a ratio measure, the SEI proportion simultaneously reflects the tendency of providers to perform CABG surgery on patients with SEIs and to eschew operation on patients lacking SEIs. Thus, a low SEI rate could indicate failure to operate on eligible patients with extensive CAD, enthusiastic acceptance of patients with minimal disease, or both. In addition, hospitals and their surgeons may vary in terms of local referral patterns. An aggressive PCI program, for example, could siphon away all but the 3-vessel and left main disease patients, resulting in a high SEI proportion, whereas in areas with fewer interventional cardiologists, patients may be preferentially shunted towards surgery, resulting in a low SEI proportion. Our prior beliefs as to the direction of this effect were not strong; in fact, it could be argued that a hospital with an enthusiastic PCI program would have a low SEI proportion if interventionists were handling patients with 3-vessel and left main coronary disease in preference to CABG surgery. Despite these limitations, it is reasonable to hypothesize that hospitals with a high SEI rate have a low incidence of inappropriate surgery; no conclusions can be drawn about hospitals with low SEI rates. In any case, the most important application of the SEI metric will be to stimulate individual hospitals to examine their own data in support of internal quality improvement.
During the 1980s and 1990s, RAND developed appropriateness criteria [26
] for CABG surgery. In a subsequent multi-institutional study, 74–95% of CABG surgeries were deemed necessary or crucial [27
]. Our results are consistent with the RAND findings. However, the CCORP (and STS) data currently lack certain information available to RAND investigators, including left anterior descending (LAD) coronary artery involvement and the intensity of medical management. As a result of this study, the Clinical Advisory Panel, the oversight body of the CCORP, has approved recommendations to add LAD involvement as a required new element for statewide data collection.
In the multivariable analysis, patients in older age groups (over age 65) undergoing CABG surgery were more likely than younger patients to have a "probable SEI." Similarly, CABG patients with significant chronic comorbidities such as hypertension, PVD, diabetes, CVD and CHF were more likely than CABG patients without those comorbidities to have a "probably SEI." The most plausible explanation for this finding is that surgeons may "screen out" elderly and chronically ill patients without SEIs [due to concern about their perioperative risk in the setting of uncertain survival benefit) and refer them back to cardiologists for possible PCI or medical therapy. Of course, primary care physicians and cardiologists may also be less likely to refer elderly and chronically ill patients without SEIs to surgeons, for the same reason. The higher "probable SEI" rate among men than women was unexpected, but may reflect unmeasured gender differences in the spectrum of coronary disease (e.g., prevalence of LAD involvement with one or two-vessel disease).
In summary, the "probable SEI" proportion varies substantially among California hospitals that perform CABG surgery. Extreme values of this metric do not necessarily indicate a problem with quality. In particular, we need to know whether low SEI rates at the hospital level correlate with clinical inappropriateness, using more detailed methods such as the RAND approach. Additional research is also needed to determine whether the observed variation in patient selection results from market factors, referral patterns, patient preferences, or local clinical culture. Also, hospitals with SEI proportions at the extreme high- or low-end of the distribution may wish to examine their own data in more detail to assure themselves that patient selection is occuring in accord with current standards of evidence and practice.