Novel noninvasive indices of perfusion dynamics wave analysis detect above knee arterial stenosis in the presence of widespread arteriosclerosis
Authors: Heitner T , Livneh A , Vargas M , Lorber J , Karmeli R , Landesberg A 
Published: October 2022

Abstract

Introduction
Peripheral arterial disease (PAD) is a leading cause of vascular morbidity and mortality. The Ankle Brachial Index (ABI) is a common index for screening and monitoring PAD. The AHA and ECS guidelines recommend measuring the ABI for assessing atherosclerotic cardiovascular risk. However, the ABI sensitivity is low, especially in the elderly and diabetics with arteriosclerosis. The restenosis rate after revascularization is high and there is an unmet need for continuous monitoring for detection of restenoses in these patients. ABI requires Doppler Ultrasound measurements.

Purpose
We hypothesized that monitoring the arterial perfusion dynamics instead of the peak systolic pressure, could improve PAD surveillance and management.

Methods
A novel method for quantifying the arterial perfusion dynamic from impedance plethysmography measurements was developed. A novel segmentation of the arterial perfusion upstroke has revealed that it consists of two characteristic phases, an initial slow phase that is followed by a fast vigorous rise. The phase transition point was defined by the maximum acceleration time point (MAT). The slow phase duration was denoted as the `Perfusion Deficit Index` (PDI). The arterial perfusion signals were derived from calves of PAD patients that were admitted for revascularization. We compared the novel PDI and MAT indices with measured ABI before and after the revascularizations.

Results
Sixteen patients with isolated above-knee stenoses were recruited and treated in eighteen legs. The perfusion signals before the revascularization were characterized by prolonged PDI, and overt shortening of the PDI was observed after successful revascularization, as depicted in Figure 1. The PDI was significantly negatively correlated with the ABI. In patients with satisfactory postoperative increase in ABI (&gt;0.15) the PDI dropped from 105±33 ms to 26±16 ms (n=13, p&lt;0.001). The “pulse transit time” (PTT) that relates to arteriosclerosis did not change between measurements in all the patients. Thus, the measurement of the PTT and PDI can differentiate between the two elements of atherosclerosis: generalized arteriosclerosis and development of localized arterial narrowing. Interestingly, in the contralateral untreated leg the ABI and PDI had a similar significantly negative correlation, without significant difference before and after the procedures. Assessment of the ABI and PDI abilities to detect focal stenosis revealed that the PDI detected stenosis with 91% sensitivity and 85% specificity, while the ABI only had 74% sensitivity and 85% specificity (Figure 2).

Conclusions
The PD can be used for assessing revascularization outcome and monitoring atherosclerosis severity. The MAT and PDI are novel sensitive and specific indices for detecting arterial stenoses, even in the presence of arteriosclerosis, unlike the ABI. The applicability of this simple to use method for screening and telemedicine should be further validated.

Funding Acknowledgement
Type of funding sources: None.