Effect of risk-adjusted diabetes on mortality and morbidity after coronary artery bypass surgery

Diabetes is commonly regarded as a risk factor for mortality and morbidity after coronary artery bypass surgery.

Between April 1997 and December 2002, 6,033 consecutive patients underwent isolated coronary artery bypass surgery. Eight hundred and fourteen (13.5%) patients had diabetes (530 oral-dependent, 284 insulin-dependent). Patients with diet-controlled diabetes were classified as nondiabetics. Deaths occurring over time were described using Kaplan-Meier techniques. To control for differences in patient characteristics, we constructed a propensity score (for diabetes) and this was included along with the comparison variable in multivariate logistic regression and Cox proportional hazards analyses.

In-hospital mortality was significantly higher for diabetic patients in the univariate analyses; however, this association disappeared after adjusting for the propensity score. Further analyses found that insulin-dependent diabetes was associated with an increased incidence of acute renal failure (adjusted odds ratio 4.15; p = 0.002), deep sternal wound infection (adjusted odds ratio 2.96; p = 0.039), and prolonged postoperative stay (adjusted odds ratio 1.60; p = 0.017). Oral-controlled diabetes was not associated with any of these outcomes. Four hundred and ninety-eight (8.3%) deaths occurred during the study follow-up. After adjusting for patient characteristics, the adjusted hazard ratio of midterm mortality for diabetes was 1.35; p = 0.013.

Insulin-dependent diabetes has a significant impact on in-hospital morbidity. Although diabetic patients are not at increased risk of in-hospital mortality, longevity is significantly decreased during a five-year follow-up period.