Prognostic impact of type 1 and type 2 diabetes mellitus in atrial fibrillation and the effect of severe hypoglycaemia: a nationwide cohort study

Aims To compare prognosis between individuals without diabetes, type 1 and type 2 diabetes in a nationwide atrial fibrillation cohort in Sweden and study the significance of severe hypoglycaemia. Methods Using data from all-inclusive national registers, 309,611 patients with non-valvular atrial fibrillation were enrolled during 2013-2014. Of these, 2,221 had type 1 and 58,073 had type 2 diabetes. Patients were followed for all-cause mortality until 27 March 2017, and for myocardial infarction, ischaemic stroke and first-ever diagnosis of heart failure or dementia until 31 December 2015. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using Cox and competing risk regression. Results Using individuals without diabetes as reference (HR = 1), the adjusted HRs in type 1 vs. type 2 diabetes were for mortality 1.87 (CI 1.73-2.02) vs. 1.51 (CI 1.47-1.55), heart failure 1.59 (CI 1.42-1.78) vs. 1.41 (CI 1.34-1.48), myocardial infarction 2.49 (CI 2.17-2.85) vs. 1.70 (CI 1.59-1.81), ischaemic stroke 1.59 (CI 1.35-1.87) vs. 1.31 (CI 1.22-1.40), and dementia 1.46 (CI 1.15-1.85) vs. 1.28 (CI 1.18-1.40). Among individuals with type 2 diabetes, those with previous severe hypoglycaemia had increased risk of mortality (HR 1.26; CI 1.17-1.36) and dementia (HR 1.37; CI 1.08-1.73) compared with those without previous severe hypoglycaemia. Conclusion Presence of diabetes-regardless of type- in atrial fibrillation is associated with an increased risk of premature death, cardiovascular events and dementia. This increase is more pronounced in type 1 than in type 2 diabetes. A history of severe hypoglycaemia is associated with a worsened prognosis in type 2 diabetes.