Discriminant analysis of the changing risks of cornary artery operations: 1971-1979

The risk or perioperative myocardial infarction (PMI) and operative mortality (OM) associated with coronary artery bypass grafting (GABG) has declined since the introduction of this procedure 15 years ago. Rigorous scientific investigation of the reasons for this trend has been hindered by the complex interactions between changing indications for operation, criteria for patient selection, and management methods. Using univariate and multivariate logistic regression analyses, we investigated the effects of 42 variables on PMI and OM for two cohorts undergoing GABG between 1971 and 1975 (Group A) and 1977 and 1979 (Group B). According to previously identified risk factors, Group B patients were at higher potential risk than those in Group A. Nevertheless, the PMI and OM rates declined from 8.7% ± 0.9% to 4.6% ± 0.7% (p = 0.005) and from 2.4% ± 0.5% to 1.2% ± 0.4% (p = 0.07), respectively. In calendar year 1979 (N = 438), the PMI and OM rates were 2.8% ± 0.8% and 0.7% ± 0.4%. More importantly, the independent determinants of PMI and OM for the two time intervals were distinctly different. Factors which affected the PMI rate in Group A were no longer determinants of PMI in Group B; with the exception of emergency operation and, to a modest extent, congestive heart failure (CHF), predictors of OM in Group A were not determinants of OM in Group B. Thus the adverse impact of multiple patient-related and disease-related determinants of PMI and OM has been neutralized over this decade by the real improvements in patient management. The specific factors and management concepts responsible for these superior results in sicker patients remain uncharacterized; however, in general terms, more sophisticated medical, anesthetic, and nursing management and more refined surgical expertise have essentially nullified the concept of high-risk candidates. Furthermore, the more propitious early results being attained currently may translate directly into parallel long-term improvements in functional benefit and survival.