Ankle Brachial Index, Toe Brachial Index, and Cardiovascular Mortality in Participants With and Without Diabetes Mellitus

Background— The prognostic utility of ankle brachial index (ABI) may be hampered in persons with diabetes due to peripheral arterial stiffening in the ankles. Stiffening of toe arteries occurs infrequently in diabetes. Objectives— We aim to determine the nature of the relationship of the toe brachial index (TBI) and ABI with cardiovascular (CVD) mortality, and to determine whether the associations are modified in individuals with diabetes. Methods— Individuals with clinically suspected atherosclerotic PAD who underwent ABI and TBI measurements in a vascular laboratory were followed longitudinally for CVD mortality. Results— Among 469 (89% men) participants, the mean age was 68 ± 9 years and 36% had diabetes. The mean ABI was 0.83 ± 0.28 and the mean TBI was 0.60 ± 0.24. During 7.0 years (median) follow-up, there were 158 CVD deaths. Association of the ABI categories with CVD events differed in diabetic vs. non-diabetic participants (P-interaction = .002). In contrast, association of the TBI categories with CVD events were similar irrespective of diabetes status (P-interaction = .17). Among diabetic patients, a U-shaped relationship was observed between ABI categories and CVD death; both those with low (< 0.90) and high (> 1.30) ABI were at higher risk than those with normal (0.90–1.30) ABI. In non-diabetic patients, association of ABI categories with CVD death was linear, such that those with ABI > 1.30 were at the lowest between TBI categories and CVD death irrespective of diabetes status. These findings suggest that stiffened ankle arteries may limit the predictive value of the ABI in individuals with diabetes; a limitation that may be overcome by measurement of the TBI.