Abstract
Background and aimsThe ankle brachial index (ABI) is often used as a proxy for medial arterial calcification (MAC) in studies investigating MAC as a cardiovascular risk factor, but evidence supporting this hypothesis is sparse. This study aims to investigate the use of an elevated ABI as proxy for MAC, as visualized with computed tomography (CT). MethodsCross-sectional data of 718 participants with, or at risk of cardiovascular disease was used. The ABI was calculated using cutoffs >1.4 and > 1.3. The presence of MAC was assessed in the crural and femoral arteries by CT imaging. Modified Poisson regression was used to assess the association between an elevated ABI and the presence of MAC, and test characteristics were calculated. ResultsMAC was found in 25.0% of participants. An ABI >1.4 was found in 8.7% of participants, of whom 45.2% had MAC. An elevated ABI was significantly associated with the presence of MAC (RR 1.74, CI: 1.26–2.40). However, poor positive specific agreement (23.3%, CI: 13.9–34.3), sensitivity (15.7%, CI: 10.4–21.1) and positive predictive value (45.2%, CI: 32.8–57.5) were found. Despite good specificity (93.6%, CI: 91.6–95.7) the area under the receiving operator curve remained poor (54.7%, CI: 51.8–57.6). Negative specific agreement (84.5%, CI: 81.4–87.0) and negative predictive value (77.0%, CI: 73.7–80.2) were acceptable. ConclusionsAn elevated ABI is insufficient to serve as a true diagnostic proxy for MAC. Studies that have drawn conclusions on the association between MAC and cardiovascular disease, solely based on the ABI, are likely to underestimate the found effects.
Highlights
The ankle-brachial index (ABI) is defined as the ratio of ankle systolic blood pressure (SBP) to brachial SBP
This study is comprised of participants from two ongoing cohort studies; the Second Manifestations of ARTerial disease (SMART) study and the Diabetes Care System (DCS) cohort
Participants who were newly referred to the University Medical Center Utrecht with either manifest vascular disease or important cardiovascular risk factors were invited to participate in the SMART cohort and were asked to undergo an additional unenhanced thin-slice computed tomography (CT) scan of the legs
Summary
The ankle-brachial index (ABI) is defined as the ratio of ankle systolic blood pressure (SBP) to brachial SBP. A decreased ABI has been associated with an increased risk for future cardiovascular disease (CVD). In contrast to the established relationship between a decreased ABI and the presence of atherosclerotic disease [3], less is known about the underlying pathophysiological mechanism responsible for the observed increased cardiovascular risk in a population with an elevated ABI. Modified Poisson regression was used to assess the association between an elevated ABI and the presence of MAC, and test characteristics were calculated. Poor positive specific agreement (23.3%, CI: 13.9–34.3), sensitivity (15.7%, CI: 10.4–21.1) and pos itive predictive value (45.2%, CI: 32.8–57.5) were found. Studies that have drawn conclusions on the association between MAC and cardiovascular disease, solely based on the ABI, are likely to underestimate the found effects
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