Evaluation of Peripheral Calcium Score as a Measure of Peripheral Arterial Disease Burden and Amputation Risk Open Access
Lee, Sujin (Spring 2019)
Peripheral arterial disease (PAD) is a global atherosclerotic pandemic characterized by chronic occlusive arterial disease of the lower extremities. The ankle-brachial pressure index (ABI) and toe-brachial pressure index (TBI) are non-invasive tools used to diagnose PAD by measuring blood pressures at the ankle or toe compared to the arm at a pressure where no flow is detected by ultrasound. The ABI and TBI are flawed because they do not adequately represent arterial flow in calcified vessels. The purpose of this research is to evaluate whether a comprehensive peripheral calcium scoring (PCS) system would complement ABI and TBI to achieve a superior prognostic measure of PAD. We conducted a retrospective cohort of 50 patients, who reported to vascular surgery clinics from 2004 to 2014, to compare their distributions of ABI, TBI, and PCS, and to assess how well these prognostic indicators predicted the dichotomous outcome of an amputation of a lower limb. The particular interest was to evaluate how well PCS improved the prediction of amputation after controlling for ABI and TBI levels. We measured the calcium burden in peripheral vessels by applying the coronary calcium scoring module to non-contrast CT scans of the infra-renal aorta and lower extremity runoff. We built a predictive model using a dichotomized PCS variable as a predictor at an a priori cutoff value of 1000. Using multivariate logistic regression, the odds ratio for the association between tibial PCS and amputation was estimated at 6.61 (3.77-11.59, p<0.001, controlling for ABI and TBI, suggesting that PCS can be a useful prognostic indicator for PAD patients beyond ABI and TBI. We also built models using ABI, TBI, and continuous PCS separately and in combination to predict amputation. The best fitting model included ABI, TBI, and tibial PCS (AUC=0.87, p<0.001). This study underscores the importance of tibial PCS as an individual prognostic tool, as well as a significant supplemental tool, to improve the prognostication of patients with PAD.
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