Calcification of the digital arteries is present in a majority of patients with Chronic Limb Threatening Ischemia (CLTI)1, causing a false-high toe pressure value. Furthermore, measurement of toe pressure may be hampered by toe wounds or minor amputations. Pedal acceleration time (PAT) is an alternative method2 which uses duplex imaging of the pedal arteries, wherein flow is visualized, and acceleration time is measured as the time from onset of systole, to the peak of systole. Although PATs learning curve of 20 studies is minor, this technique does require trained personnel and duplex imaging equipment, which prohibits the use in an outpatient setting. We investigated the prognostic value of the Digital Acceleration Time (DAT) from the photoplethysmographic (PPG) pulse wave form available during standard toe pressure measurements.

Single center retrospective study of patients with toe pressure measurements in the years 2017-2018. GermanVasc scores were calculated based on medical history. Wound-Ischemia-foot-Infection score (WIfI) was retrospectively assessed based on clinical description and wound photos. Global Limb Anatomic Staging System (GLASS) was scored in all patients who underwent angiography. Our primary outcome was Major Adverse Limb Event (MALE), defined as the composite of major amputation, surgical or endovascular revascularization, and death. DAT was measured by digitally analyzing the pulse wave in the toe pressure report PDF file. The prognostic value of DAT was analyzed using Receiver Operating Characteristics (ROC) curves. Threshold values were chosen based on 90% sensitivity and 90% specificity in predicting 1 year MALE. Kaplan Meier survival analysis was performed for MALE-free-survival. ROC curves were constructed for the angiographic diagnosis of GLASS stadium ≥1, and compared with toe pressure. Subgroup analysis of patients with an inability for toe pressure measurement was also performed.

Six-hundred-thirteen measurements in 400 patients were analyzed in 3 groups based on DAT; < 158 ms (n = 96, 90% sensitivity MALE), 158-268 ms (n = 428) and >268 ms (n = 86, 90% specificity MALE). Patient characteristics differed significantly for age, absolute toe pressure, GermanVasc-, WIfI- and GLASS-score, all being worse in the longer acceleration time groups (table 1). MALE-free survival differed significantly with 88.2%, 68.6% and 49.7% for short, medium and long acceleration times respectively (p < 0.001, Figure 1). DAT and toe pressure scored similar in diagnosing GLASS stadium ≥1 (AUC 68.0% [95% confidence interval 58.6-77.5%] versus 67.3% [56.9-77.8%], p=0.9. In 46 patients (8%) no toe pressure measurement was possible. A DAT of >268 ms was again a significant predictor of 1-year MALE-free survival (30% vs 80%, p = 0.014)

Photoplethysmography derived Digital Acceleration Time accurately predicts 1 year major adverse limb events. This technique requires no formal training, could be integrated into (handheld) devices used for toe pressure measurements, can be combined with absolute toe-pressure readings, as well as a stand-alone measurement in cases toe pressure cannot be measured. Future prospective studies should define optimal threshold values, comparable to the values in PAT, that distinguish absence of ischemia, moderate or severe ischemia.

1. Ferraresi, R., Ucci, A., Pizzuto, A., Losurdo, F., Caminiti, M., Minnella, D., Casini, A., Clerici, G., Montero-Baker, M., & Mills, J. (2020). A Novel Scoring System for Small Artery Disease and Medial Arterial Calcification Is Strongly Associated With Major Adverse Limb Events in Patients With Chronic Limb-Threatening Ischemia. In Journal of Endovascular Therapy (Vol. 28, Issue 2, pp. 194-207) 2. Teso, D., Sommerset, J., Dally, M., Feliciano, B., Vea, Y., & Jones, R. K. (2021). Pedal Acceleration Time (PAT): A Novel Predictor of Limb Salvage. In Annals of Vascular Surgery (Vol. 75, pp. 189-193).