Toe pressure measurement in the context of digital artery calcification

Background: In patients suspected for peripheral arterial disease and who are at risk for arterial calcification, measurement of the toe pressure (TP) is preferred over the ankle-brachial index, owing to an alleged reduced susceptibility for calcification in the digital arteries. Recent studies, however, have shown that calcification of digital arteries is prevalent in chronic limb-threatening ischemia patients. This study examined the influence of digital artery calcification in suspected chronic limb-threatening ischemia on the measured TP. Methods: We conducted a single-center, retrospective analysis of patients reporting to a multidisciplinary vascular clinic. All patients had bilateral TP measurements, and patients without radiographs of the foot were excluded. Cox proportional hazard modelling was performed for 1-year major adverse limb events (MALEs) between patients with and without digital artery calcification. Propensity score matching was performed to create comparable groups of patients with and without digital artery calcification and included known confounders for the presence of digital artery calcification. TP was plotted against a calculated probability of 1 year MALE-free survival for both matched groups. Results: Four hundred ninety-four limbs in 382 patients were included, of which 143 had radiographical signs of digital artery calcifications (28.9%), and 351 (71.1%) had not. Digital artery calcification had a 2.51 hazard ratio (95 confidence interval, 1.68-3.73) for MALE-free survival. One hundred sixty-five patients were matched. The probability of 1-year MALE-free survival increased with decreasing systolic TP in both calcified and noncalcified digital arteries. Overall, a 20 to 30 mm Hg difference between groups is visualized for each estimate of risk. Conclusions: Calcification of the arteries of the first toe is present in 27.2% of patients, which significantly reduces MALE-free survival, with a hazard ratio of 2.5. For an adequate assessment of ischemia risk, when medial arterial calcification is present in radiographic imaging of the foot, we advise to subtract 20 to 30 mm Hg of the TP measurement.