Long-term mortality in patients with type 2 diabetes undergoing coronary angiography: the impact of glucose-lowering treatment

The aim of this study was to analyse whether the increased mortality rates observed in insulin-treated patients with type 2 diabetes and coronary artery disease are explained by comorbidities and complications. A retrospective analysis of data from two Swedish registries of type 2 diabetic patients (n = 12,515) undergoing coronary angiography between the years 2001 and 2009 was conducted. The association between glucose-lowering treatment and long-term mortality was studied after extensive adjustment for cardiovascular- and diabetes-related confounders. Patients were classified into four groups, according to glucose-lowering treatment: diet alone; oral therapy alone; insulin in combination with oral therapy; and insulin alone. After a mean follow-up time of 4.14 years, absolute mortality rates for patients treated with diet alone, oral therapy alone, insulin in combination with oral therapy and insulin alone were 19.2%, 17.4%, 22.9% and 28.1%, respectively. Compared with diet alone, insulin in combination with oral therapy (HR 1.27; 95% CI 1.12, 1.43) and insulin alone (HR 1.62; 95% CI 1.44, 1.83) were associated with higher mortality rates. After adjustment for baseline differences, insulin in combination with oral glucose-lowering treatment (HR 1.22; 95% CI 1.06, 1.40; p < 0.005) and treatment with insulin only (HR 1.17; 95% CI 1.02, 1.35; p < 0.01) remained independent predictors for long-term mortality. Type 2 diabetes patients treated with insulin and undergoing coronary angiography have a higher long-term mortality risk after adjustment for measured confounders. Further research is needed to evaluate the optimal glucose-lowering treatment for these high-risk patients.