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 ( HbA 1c ). Using the time‐weighted mean of serial HbA 1c 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 HbA 1c was calculated using all HbA 1c measurements following CHF diagnosis. Patients were grouped into five categories of HbA 1c (≤6.0%, 6.1–7.0%, 7.1–8.0%, 8.1–9.0%, and >9.0%). The relationship between time‐weighted mean HbA 1c 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 HbA 1c category (7.1–8.0%) as the reference, showed a U‐shaped relationship between HbA 1c and outcome [ HbA 1c <6.0%, hazard ratio ( HR ) 2.5, 95% CI 1.8–3.4; HbA 1c 6.1–7.0%, HR 1.4, 95% 1.1–1.7; HbA 1c 8.1–9.0%, HR 1.3, 95% CI 1.0–1.6; and HbA 1c >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 HbA 1c and mortality, with the lowest risk in patients with modest glycaemic control ( HbA 1c 7.1–8.0%) and those treated with insulin sensitizers.