Interaction between diabetes and a high ankle-brachial index on mortality risk

Objective: Low ankle-brachial index (ABI) is a predictor of increased mortality. The impact of a high ABI on mortality is less studied. Moreover, diabetes is frequently associated with high ABI and, because of specific mechanisms in diabetic vascular diseases, the relationship with prognosis may be unique. Therefore, our aim was to compare mortality in individuals with and without diabetes according to abnormally low and high ABI.

Design and methods: We studied the association between ABI and all-cause and cardiovascular mortality in 6986 participants from the REACH registry, a cohort of 45 years and older stable outpatients at high cardiovascular risk (2875 (41.1%) with diabetes) followed for 4 years.

Results: ABI was normal (0.91-1.29) in 49.5%, low (≤0.9) in 47.5%, and high (≥1.3) in 2.9% of participants. During follow up, 9.9% of participants died (6.5% from cardiovascular causes). A low ABI was associated with cardiovascular mortality (adjusted hazard ratio, HR, 1.98, 95% CI 1.62-2.41) and all-cause mortality (HR 2.01, 95% CI 1.72-2.36), without heterogeneity according to diabetes. In contrast, high ABI was associated with higher risk of all-cause mortality in individuals with diabetes (HR 2.11, 95% CI 1.16-3.84), but not without diabetes (HR 0.82, 95% CI 0.36-1.85; p-value for interaction 0.07). The trend was similar for cardiovascular mortality (HR 2.13, 95% CI 1.03-4.44 and HR 1.05, 95% CI 0.43-2.59 with and without diabetes, respectively; p-value for interaction 0.24).

Conclusions: In the REACH registry, low ABI was associated with mortality, similarly in individuals without and with diabetes, whereas the association with high ABI was only observed in patients with diabetes.