Approximation of the Ankle-Brachial Index in the Setting of Medial Arterial Calcific Sclerosis

Abstract

The presence of medial arterial calcific sclerosis is known to cause inaccuracy in the interpretation of noninvasive vascular testing. This substantially limits the utility of an important baseline diagnostic test for peripheral arterial disease. Therefore, the objective of this investigation was to derive a method to effectively factor out calcification in the interpretation of the ankle and digital brachial indices. The noninvasive vascular testing results of 160 subjects were stratified into the absence of calcification, mild calcification, moderate calcification, and severe calcification based on plain film radiographic findings of the infrageniculate vessels. Measurements were then performed of the pulse volume recording (PVR) waveforms at brachial, ankle and digital anatomic levels to include PVR wavelength and PVR upstroke length, with a calculation of the ratio of PVR upstroke length to PVR wavelength. These measurements were compared between groups and then correlated to the ankle and digital brachial indices. A significant difference was observed in the PVR upstroke ratio between the 3 anatomic levels (0.1818 vs 0.2622 vs 0.3191; p < .001), but not between the 4 calcification groups (0.2457 vs 0.2363 vs 0.2694 vs 0.2631; p = .242). A significant negative correlation was observed between the PVR upstroke ratio and the ankle brachial index (ABI) (Pearson -0.454; p = .002) with linear regression indicating the relationship is defined by the formula: Effective ankle brachial index = 1.17 – (1.33 × PVR upstroke ratio at ankle level). A significant negative correlation was also observed between the PVR upstroke ratio and the digital brachial index (Pearson -0.553; p < .001) with linear regression indicating the relationship is defined by the formula: Effective toe brachial index = 1.04 – (1.61 × PVR upstroke ratio at digital level). The results of this investigation demonstrate the feasibility of, and provide equations to approximate, the effective ankle brachial and toe brachial indices in the setting of medial arterial calcification.