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. 2025 Jul 10;3(2):qyaf057.
doi: 10.1093/ehjimp/qyaf057. eCollection 2025 Jul.

Estimation of toe brachial index based on forefoot Doppler waveforms

Alexander D Rodway  1   2 , Rachael Jarrett  1 , Darren Cheal  2 , Gary D Maytham  1   3 , Benjamin C T Field  1   4 , Martin B Whyte  4 , Justin Read  5 , Philip J Aston  5 , Simon S Skene  4 , Jenny Harris  6 , Christian Heiss  1   4
Affiliations

Estimation of toe brachial index based on forefoot Doppler waveforms

Alexander D Rodway et al. Eur Heart J Imaging Methods Pract. .

Abstract

Aims: The toe brachial index (TBI) is a standard diagnostic tool for assessing distal perfusion in peripheral arterial disease (PAD) but has several limitations. Doppler waveform characteristics of forefoot arteries, such as acceleration index (AccI), peak systolic velocity (PSV), and acceleration time (AT), present a potentially reliable and more accessible alternative for estimating TBI. This study evaluated the association between Doppler waveform characteristics and standard TBI, developed empirical equations for estimating TBI (eTBI), and assessed their accuracy, reproducibility, and clinical applicability.

Methods and results: This study presents a prospective analysis of angle-corrected Doppler AccI, PSV, and AT in forefoot metatarsal arteries together with standard automated TBI in 155 limbs of PAD patients treated at Surrey and Sussex Healthcare NHS Trust, Redhill, UK. Doppler-derived AccI, PSV, and AT were significantly associated with standard TBI (R 2 = 0.88, 0.58, 0.62; each P < 0.001). Empirical equations for eTBI calculation demonstrated excellent agreement with standard TBI, with minimal average deviations [-0.01 ± 0.10 (SD) for AccI]. Multivariable analysis confirmed that eTBI derived from AccI predicted TBI largely independent of age, sex, diabetes mellitus, Fontaine stage, diastolic blood pressure, and kidney function (R 2 = 0.89). After revascularization, both eTBI and standard TBI increased significantly, with strong correlation (r = 0.95, P < 0.001). Inter- and intra-observer and inter-device variability for eTBI measurements was low, outperforming standard TBI.

Conclusion: Doppler waveform-derived eTBI, particularly using AccI, provides a reproducible, accurate, and clinically responsive alternative to standard TBI. These findings support its integration into routine vascular diagnostics, enhancing accessibility and diagnostic precision in PAD care. Automated eTBI acquisition could enhance screening efficiency in non-specialist settings.

Keywords: Doppler ultrasound; acceleration index; angioplasty; peripheral artery disease; toe brachial index; wave form analysis.

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Conflict of interest statement

Conflict of interest: C.H. is a member of the board of the European Society of Vascular Medicine. C.H. is the chairperson elect of the nucleus of the European Society of Cardiology Working Group on Aorta and Peripheral Vascular Disease. C.H. and P.J.A. have received research funding from the European Partnership on Metrology, co-financed from European Union’s Horizon Europe Research and Innovation Programme and UK Research and Innovation. C.H. has received research funding to the institution from Medical Research Council, Lipton, iThera, and Ageless Science and honoraria for lectures by Bayer not related to the manuscript. C.H. declares being a council member and president of Royal Society of Medicine, Vascular Medicine Council. All other authors declare no competing interests.

Figures

Graphical Abstract
Graphical Abstract
Figure 1
Figure 1
Regression analyses with best-fit curve estimates for the relationships between standard TBI and metatarsal artery AccI (A), PSV (B), and AT (C) (n = 155).
Figure 2
Figure 2
Regression analyses for the relationships between standard TBI and eTBI calculated from metatarsal artery AccI (A), PSV (C), and AT (E) and corresponding Bland–Altman plots (B, D, and F) (n = 155).
Figure 3
Figure 3
Bland–Altman plots for the assessment of (A) intra-observer variation in eTBI based on AccI (n = 21); (B) inter-observer variation in eTBI based on AccI (n = 25); (C) inter-device variation in eTBI based on AccI, comparing vascular laboratory-standard equipment (GE Vivid S9) with a POC device (VSCAN Air, n = 25); and (D) intra-observer variation in standard TBI measured with the Systoe device (n = 34).
Figure 4
Figure 4
Regression analyses with best-fit curve estimates for the relationships between standard TBI handheld Doppler waveform characteristics: slope (A), PF (B), and rise time (C). (D) Bland–Altman plot showing deviation of estimated eTBI based on slope. (E) Comparison of curve estimates between duplex (Figure 1A) and handheld Doppler-based assessment using different insonation angles in the calculations (n = 100).
See this image and copyright information in PMC

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