Mean HbA1c and mortality in diabetic individuals with heart failure: a population cohort study

Aims Controversy exists regarding the importance of glycaemic control in patients with type 2 diabetes mellitus (T2DM) and chronic heart failure (CHF) based on conflicting reports using single baseline glycosyated haemoglobin (HbA1c). Using the time‐weighted mean of serial HbA1c measurements has been found to be a better predictor of diabetic complications as it reflects the glycaemic burden for that individual over time. We therefore sought to confirm this in a large cohort of patients with T2DM and incident CHF. Methods and results A time‐weighted mean HbA1c was calculated using all HbA1c measurements following CHF diagnosis. Patients were grouped into five categories of HbA1c (≤6.0%, 6.1–7.0%, 7.1–8.0%, 8.1–9.0%, and >9.0%). The relationship between time‐weighted mean HbA1c and all‐cause death after CHF diagnosis was assessed. A total of 1447 patients with T2DM met the study criteria. During a median follow‐up of 2.8 years, there were 826 (57.1%) deaths, with a crude death rate of 155 deaths per 1000 person‐years [95% confidence interval (CI) 144–166]. A Cox regression model, adjusted for all significant predictors, with the middle HbA1c category (7.1–8.0%) as the reference, showed a U‐shaped relationship between HbA1c and outcome [HbA1c 9.0%, HR 1.8, 95% CI 1.4–2.3]. Further analysis revealed a protective effect of insulin sensitizers (i.e. metformin) (HR 0.7, 95% CI 0.61–0.93) but not other drug classes. Conclusions In patients with T2DM and CHF, our study shows a U‐shaped relationship between HbA1c and mortality, with the lowest risk in patients with modest glycaemic control (HbA1c 7.1–8.0%) and those treated with insulin sensitizers.