Trends in coronary artery bypass surgery results: a recent, 9-year study

The demographics of patients undergoing coronary artery bypass grafting (CABG) have changed over time and may contribute to differing operative mortality and the combination of mortality and morbidity (M + M). In this study, the trends in results are analyzed and causes are suggested.

Prospectively collected data concerning 4,839 CABG operations was divided into three time cohorts (1990 to 1992, 1993 to 1995, 1996 to 1998) and analyzed by univariate and multivariate techniques.

Mean age and female gender frequency increased in the later time cohorts (60.7 +/- 9.0 to 63.4 +/- 9.9 years and 16.5% to 21.4%, respectively). The following comorbidities were more prevalent in the later time cohorts: diabetes (26.7% versus 18.6%), renal failure (8.5% versus 2.2%), peripheral vascular disease (20.7% versus 11.0%), previous cerebrovascular accident (6.7% versus 5.0%), urgent procedures (41.5% versus 26.9%), unstable angina (47.8% versus 31.7%), urgent CABG following myocardial infarction (17.1% versus 7.3%), previous percutaneous transluminal coronary angioplasty (8.0% versus 4.5%), ejection fraction less than 35% (20.5% versus 10.4%), (all p < 0.05). Procedurally, increased utilization of the left internal mammary artery, multiple arterial conduits, and warm blood cardioplegia occurred in the later cohorts (91.2%, 22.2%, and 80.4% versus 78.7%, 3.4%, and 38.0%, respectively). The mortality rate was 2.0% and the M + M rate was 15.6% in all 4,839 patients. The mortality and M + M for the three cohorts were 1.6%, 2.0%, and 2.3% and 18.4%, 17.2% and 12.5%, respectively. The risk-adjusted mortality and M + M decreased from 2.4% and 15.9%, respectively, in 1990 to 1992 to 1.8% and 8.4% in 1996 to 1998 (p < 0.001). The difference in adjusted event rates was minimized when the surgical factors were entered into the model.

Over time, there has been a trend toward operating on older patients with more comorbidities. Though hospital mortality has been stable, risk-adjusted M + M has been in a constant decline. This decline was associated with an increased use of left internal mammary artery grafts, multiple arterial conduits, and warm blood cardioplegia during the later years of the study.