Digest: Can’t see the wood for the trees …PAD?

They used four tests to determine PAD, two proximally by palpation of pedal pulses and ABI, and two distally by Toe Brachial Index (TBI), forefoot transcutaneous oxygen tension (TcPO2). A total of 154 patients were consecutively recruited from the diabetic foot clinic with a mean age of 63 years. Seventy-nine-per-cent were males, 77% had type 2 diabetes and there was a mean diabetes duration of 21 years. At the time of assessment, 59% had active foot ulceration. From the 154 subjects recruited, 308 limbs were examined, of which 37 were unable to undergo ABI due to previous amputation, recent bypass surgery and leg ulceration. Only 59% of subjects had active ulceration. In total, 301 limbs were assessed for pulses, TBI and TcPO2.
The study criteria for determining PAD were the absence of one or both pulses, an ABI of <0.9, TBI of <0.75 and TcPO2 of <60 mmHg. They used Arterial Duplex as the gold standard for corroborating PAD against the study tests. However, this was only performed against a subset of subjects who had Duplex waveform studies performed as part of the patient’s routine clinical care within a month of their recruitment to the study. A triphasic waveform was deemed normal, while anything else was considered to be PAD. Using these criteria, foot PAD was detected in 70% and 74% by TBI and forefoot TcPO2, respectively, and ankle PAD in 51% and 34% by pulse palpation and ABI, respectively. In those with “normal” ABI, foot PAD was present in 70% indicated by low TBI and in 73% by low TcPO2. When compared with arterial Duplex waveforms, TBI gave an excellent AUC (area under the curve of the receiver operating characteristic curve) of 0.81 (95% confidence interval: 0.73–0.89), but ABI gave a poor AUC of 0.65 (95% confidence interval: 0.55–0.76). In conclusion, the authors state that PAD in the foot may be missed if relying upon ABI as a measure of PAD and that TBI should be performed to determine foot PAD routinely. This study is interesting and again highlights the need to review how we clinically determine PAD. However, we need to be mindful of correctly identifying significant PAD, as opposed to some reduction in arterial inflow. Longitudinal data would be required to truly identify the prognostic value of foot PAD. The message is clear for those with foot ulceration; either or both TcPO2 or TBI should routinely be performed for all ulcerated patients. Hopefully, this commentary and the paper will stimulate debate and clinical practice reflection.