Glycaemic control and incidence of heart failure in 20 985 patients with type 1 diabetes: an observational study

Background Poor glycaemic control is associated with microvascular and macrovascular complications in type 1 diabetes, but whether glycaemic control is associated with heart failure in such patients is not known. We aimed to assess this association in a large cohort of patients with type 1 diabetes identified from the Swedish national diabetes registry. Methods We identified all patients (aged >= 18 years) with type 1 diabetes and no known heart failure who were registered in the national diabetes registry between January, 1998, and December, 2003. These patients were followed up until hospital admission for heart failure, death, or end of follow-up on Dec 31, 2009. We calculated incidence categorised by glycated haemoglobin A(1c) (HbA(1c)) values, and we assessed the association between patients' characteristics, including HbA(1c), and heart failure. Findings In a cohort of 20 985 patients with mean age of 38.6 years (SD 13.3) at baseline, 635 patients (3%) were admitted to hospital with a primary or secondary diagnosis of heart failure during a median follow-up of 9.0 years (IQR 7.3-11.0), with an incidence of 3.38 events per 1000 patient-years (95% CI 3.12-3.65). Incidence increased monotonically with HbA(1c), with a range of 1.42-5.20 per 1000 patient-years between patients in the lowest (<6.5%) and highest (>= 10.5%) categories of HbA(1c). In a Cox regression analysis, with adjustment for age, sex, duration of diabetes, cardiovascular risk factors, and baseline or intervening acute myocardial infarction and other comorbidities, the hazard ratio for development of heart failure was 3.98 (95% CI 2.23-7.14) in patients with HbA(1c) of 10.5% or higher compared with a reference group of patients with HbA(1c) of less than 6.5%. Risk of heart failure increased with age and duration of diabetes. Other modifiable factors associated with increased risk of heart failure were smoking, high systolic blood pressure, and raised body-mass index. In a subgroup of 18 281 patients (87%) with data for blood lipids, higher HDL cholesterol was associated with lower risk of heart failure, but there was no association with LDL cholesterol. Interpretation The positive association between HbA(1c) and risk of heart failure in fairly young patients with type 1 diabetes indicates a potential for prevention of heart failure with improved glycaemic control.