Background: The prognostic value of preoperative hemoglobin A1c (HbA1c) in patients undergoing cardiac surgery remains uncertain. This study investigated the association between preoperative HbA1c levels and the risk of postoperative low cardiac output syndrome (LCOS) and in-hospital mortality in patients undergoing elective cardiac and/or thoracic aortic surgery. 

Methods: This single-center retrospective cohort study included consecutive adult patients who underwent elective cardiac and/or thoracic aortic surgery between 1 November 2019 and 30 June 2021. Patients younger than 18 years, pregnant, or lacking a preoperative HbA1c measurement within one week before surgery were excluded. A total of 728 patients were analyzed. Baseline clinical characteristics, operative variables, and postoperative outcomes were collected. Associations between HbA1c and perioperative parameters were assessed using univariate analyses, and independent predictors of LCOS and in-hospital mortality were identified using multivariate logistic regression. 

Results: Higher HbA1c levels were associated with greater body mass index (BMI; r = 0.08, p = 0.025), higher New York Heart Association (NYHA) functional class (III vs. I–II: 6.86 ± 1.60% vs. 6.15 ± 1.13%, p = 0.001), postoperative LCOS (7.05 ± 1.72% vs. 6.15 ± 1.13%, p = 0.013), and in-hospital mortality (6.79 ± 1.50% vs. 6.15 ± 1.13%, p = 0.011). In multivariate analysis, HbA1c independently predicted LCOS (odds ratio [OR] 1.52; 95% confidence interval [CI] 1.09–2.12; p = 0.015), together with reduced left ventricular ejection fraction and postoperative atrial fibrillation. Independent predictors of in-hospital mortality included BMI, HbA1c (OR 1.81; 95% CI 1.19–2.74; p = 0.005), EuroScore II, prolonged cardiopulmonary bypass time, impaired glomerular filtration rate, postoperative septicemia, continuous renal replacement therapy, re-intubation, and prolonged mechanical ventilation. 

Conclusions: Higher preoperative HbA1c levels were independently associated with an increased risk of postoperative LCOS and in-hospital mortality in patients undergoing elective cardiac and/or thoracic aortic surgery. These findings support the role of HbA1c as a prognostic biomarker and its potential integration into preoperative risk stratification models for cardiac surgery.