Background

Increased postoperative glycemic variability (GV) has been shown to be associated with an increased risk for adverse outcomes. However, the impact of postoperative GV on the long-term mortality after cardiac surgery, particularly with regarding other associated interactive factors, remains unknown. In this study, we sought to investigate whether postoperative GV is associated with one-year mortality, and to determine whether preoperative hemoglobin A1C (HbA1C) levels or diabetes status contribute to the risk of GV-related one-year mortality following coronary artery bypass grafting (CABG).

Methods

Data from the Medical Information Mart for Intensive Care-IV (MIMIC-IV) database derived from 3,598 patients, who underwent their CABG surgery and subsequently admitted to the ICU between 2008 and 2019, were retrospectively analysed. Patients were categorized into two groups based on the postoperative GV levels: the GV-Low group (GV < 0.219, n = 2,399) and the GV-High group (GV ≥ 0.219, n = 1,199). Cox proportional hazards models were used to examine the association between postoperative GV and one-year mortality. Kaplan-Meier curves were used to assess cumulative survival, while restricted cubic splines (RCS) were employed to explore the relationship between postoperative GV changes and one-year mortality. Cox regression was then applied to assess the impact of postoperative GV changes on one-year mortality.

Results

The one-year mortality rate was 4.92% following CABG. Multivariate Cox proportional hazards analysis revealed a significant association between postoperative GV and one-year mortality, with a hazard ratio of 1.273 (95% CI, 1.155–1.405) per 1-unit increase in Log-transformed GV in the unadjusted model, 1.255 (95% CI, 1.136–1.390) in the partially adjusted model, and 1.146 (95% CI, 1.035–1.269) in the fully adjusted model. The association followed a linear pattern (p-non-linearity= 0.962). In addition, the association was stronger in patients without diabetes mellitus (DM) (hazard ratio [HR], 1.318; 95% CI, 1.072–1.622) or in patients with preoperative HbA1c levels ≤ 7.0% (HR, 1.188; 95% CI, 1.039–1.357).

Conclusion

Increased postoperative GV is associated with higher one-year mortality following CABG, particularly in patients without DM. These findings may offer valuable guidance for targeted strategy development to reduce mortality after cardiac surgery per se.