The Relation Between HbA1c and Cardiovascular Events in Patients With Type 2 Diabetes With and Without Vascular Disease

OBJECTIVE: Poor glycemic control is related to vascular events in patients with type 2 diabetes, but the presence of vascular disease might influence this relation. We evaluated the relation between glycemic control (HbA1c level) and new cardiovascular events and mortality in patients with type 2 diabetes, with and without vascular disease. RESEARCH DESIGN AND METHODS: In a cohort of 1,687 patients with type 2 diabetes enrolled in the Second Manifestations of Arterial Disease (SMART) study, the continuous relation between HbA1c and cardiovascular events (composite of myocardial infarction, stroke, and vascular mortality) and all-cause mortality was evaluated with Cox proportional hazard analyses stratified for the presence of vascular disease. RESULTS: During a median follow-up time of 6.1 years (interquartile range 3.1-9.5 years), a new cardiovascular event developed in 293 patients and 340 patients died. In all patients, the hazard ratio (HR) of the relation between HbA1c level and cardiovascular events was 1.06 (95% CI 0.97-1.17). A 1 percentage point higher HbA1c level was related to a 27% higher risk of a cardiovascular event in patients with type 2 diabetes without vascular disease (HR 1.27 95% CI 1.06-1.51), but not in patients with vascular disease (HR 1.03 95% CI 0.93-1.15, P for interaction = 0.195). A 1 percentage point higher HbA1c level was related to a 16% higher risk of death (HR 1.16 95% CI 1.06-1.28) in patients with vascular disease and a nonsignificant 13% higher risk of all-cause mortality (HR 1.13 95% CI 0.97-1.31) in patients without vascular disease. CONCLUSIONS: In patients with type 2 diabetes, there is a modest, but not statistically significant, relation between HbA1c level and cardiovascular events, and, as there was no statistically significant interaction, this relation was not different for patients with or without clinical manifestation of vascular disease.