Related Experiment Video
Updated: May 14, 2026
Cutoff Value of Phase Angle by Bioelectrical Impedance Analysis at Admission as a Prognostic Factor in Patients with Acute Heart Failure
Published on: June 10, 2025
U-shape association between hemoglobin A1c and late mortality in patients with heart failure after cardiac surgery
Milo Engoren1, Thomas A Schwann, Cynthia Arslanian-Engoren
1Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA. engorenm@med.umich.edu
Insights
In cardiac surgery patients with heart failure, the lowest mortality risk was linked to Hemoglobin A1c (HbA1c) levels between 5.8% and 6.2%. Higher or lower HbA1c levels increased the risk of death in this group.
Area of Science:
- Cardiology
- Endocrinology
- Surgical Outcomes
Background:
- Hemoglobin A1c (HbA1c) indicates glycemic control; higher levels correlate with increased mortality risk.
- A U-shaped association between HbA1c and mortality is observed in heart failure patients, with lower risk at elevated HbA1c (>7%).
- Cardiac surgery is a common intervention for heart failure symptoms.
Purpose of the Study:
- To investigate the relationship between preoperative HbA1c levels and late mortality in patients undergoing cardiac surgery.
- To compare this association in patients with and without New York Heart Association (NYHA) class III or IV heart failure.
Main Methods:
- Patients were stratified into quartiles based on preoperative HbA1c levels.
- Mortality data was collected and analyzed using chi-square tests and Cox modeling.
- Confounder variables were adjusted for in the analysis.
Main Results:
- Patients with heart failure had higher mortality (21%) compared to those without (9%).
- In patients without heart failure, HbA1c ≤5.7% was associated with the lowest mortality risk.
- In patients with heart failure, a U-shaped curve was observed; HbA1c 5.8%-6.2% showed the lowest mortality, while levels ≤5.7% and ≥7.2% significantly increased death risk.
Conclusions:
- The optimal HbA1c range for lowest late mortality in cardiac surgery patients with heart failure is 5.8%-6.2%.
- Hemoglobin A1c levels outside this range (≤5.7% or ≥7.2%) are associated with increased mortality in heart failure patients undergoing cardiac surgery.
Abstract:
Hemoglobin A1c (HbA1c) levels are used as a measure of glycemic control, with greater levels indicating poorer control and a greater risk of death. However, recent studies have found a U-shaped association between the HbA1c levels and mortality in patients with heart failure, with the lowest risk of death associated with elevated HbA1c levels, usually >7%. Cardiac surgery is frequently used to mitigate the signs and symptoms of heart failure. The purpose of the present study was to determine the association between HbA1c levels and late mortality in cardiac surgery patients with and without heart failure. Patients with and without New York Heart Association class III or IV heart failure were divided into quartiles according to the preoperative HbA1c level. Mortality was determined for each group and compared using chi-square tests and Cox modeling. Of the 311 patients with heart failure, 65 (21%) were dead at follow-up compared to 57 of 669 patients (9%) without heart failure (p <0.001). After adjusting for confounders, the patients without heart failure and with HbA1c ≤5.7% had the lowest risk of death. In patients with preoperative heart failure, we found a U-shaped association between HbA1c levels and late mortality, with those patients with HbA1c levels of 5.8% to 6.2% having the lowest risk of death. HbA1c levels ≤5.7% and ≥7.2% were associated with statistically significant greater risks of death. In conclusion, we found in patients with heart failure that the lowest risk of death was associated with HbA1c levels of 5.8% to 6.2%.
