Thermography to assess success of lower limb endovascular revascularisation in diabetics with critical ischaemia

Abstract

Introduction - The success of endovascular revascularisation of the lower limbs for critical ischaemia needs to be assessed in order to determine whether further intervention such as open bypass surgery or further endovascular treatment is required. Assessment of success is currently based on completion radiological images or physiological testing such as ABPIs or toe pressures. These tools have significant limitations particularly in diabetics. The aim of this study was to assess whether infrared thermography could be used to assess the success of endovascular revascularisation and to compare this with currently used physiological tools. Methods - Diabetic subjects undergoing endovascular revascularisation for critical ischaemia at a vascular unit were recruited. The ABPI, Toe brachial pressure index, spectral waveforms and pulsatility index were measured before endovacular revascularisation, at 24 hours after intervention and 6 weeks after revascularisation. Radiological images were also assessed. Infrared thermography of the shins, heels and plantar aspect of the feet was performed using a FLIR e-series handheld camera before, 24 hours and 6 weeks after intervention and images analysed using FLIR software. Results - 40 consecutive diabetic subjects (19 F: 21 M) undergoing endovascular revascularisation were recruited with a median age of 76 years. 19 (47.5%) had gangrene, 27 (67.5%) active ulceration and 20 (50%) rest pain. 39 subjects underwent successful revascularisation (superficial femoral, popliteal, calf artery angioplasty/stenting) while 1 procedure was unsuccessful. ABPI could only be recorded in 22 (55%) subjects due to either an absent signal or incompressible arteries and in some of these the ABPI was artefactually elevated (>1.3). Toe pressures could only be recorded in 18 (45%) subjects due to undetectable signals or missing or gangrenous/ulcerated toes. Thermography could be performed on all subjects. There was a significant increase in temperature in the treated limb between baseline and 24 hours after at the shin (p=0.008), heel (p=0.009) and plantar mid foot (p<0.0001) and at 6 weeks in the same three sites(p=0.045; p=0.006; p=0.056 respectively). There was no significant change in temperature in the untreated limb at any point.

Conclusion - ABPIs and toe pressures often cannot be used particularly in diabetics with critical ischaemia due to undetectable signals, incompressible arteries or absent or gangrenous digits. Even when these tools can be used their ability to determine success of endovascular intervention is poor. Thermography is a non invasive, no contact, easily applicable technique which can be applied consistently in all subjects and which was shown to identify success of treatment through significant increases in temperature in the treated limb.