Estimation of toe brachial index based on forefoot Doppler waveforms

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.

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.

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.