Indocyanine Green Fluorescence Imaging in Predicting Wound Healing After Limb Revascularization

Abstract

Introduction - The most severe form of peripheral arterial disease is chronic limb threatening ischemia with tissue lesion. Assessment of critically ischemic foot is challenging.The conventional assessment methods are pressure measurements from ankle and toe level, ankle-brachial index (ABI) and transcutaneous oxygen pressure (TcPO2). Indocyanine green fluorescence imaging (ICG-FI) a relatively recent imaging method and still developing in many ways. The principle of ICG-FI is to illuminate the tissue of interest with light at the excitation wavelength (about 750 to 800nm) while observing it at longer emission wavelengths (over 800nm). ICG-FI gives a view of foot hemodynamic. After an intravenous injection of ICG, perfusion of the foot can be visualized with infrared camera and recorded for further analysis. Intensity of the fluorescence as a function of time can be analysed from the recorded images allowing a time-intensity curve to be drawn. We have earlier published analysis on the repeatability of ICG-FI and use of ICG-FI in immediate quality control after revascularization. In the current study we have analysed the use of ICG-FI in predicting wound healing after revascularization of CLTI and tissue lesion. Methods - Between January 2015 and February 2016 73 patients with CLTI and tissue lesion underwent either surgical (n=24) or endovascular (EVR) (n=49) revascularization. ICG-FI was done using Spy Elite before the revascularization, immediately after and during the follow-up. Maximum intensity, intensity rate and the relative change in the intensity rate were extracted from the automatic time intensity curve report. Results - During the mean follow-up of 16 months 77% of the wounds healed. 12 patients died and 9 had major amputation of the index leg. 4 mo, 6mo and overall wound healing rates were 51% and 63% respectively. The mean maximum intensity increased in the wound area from 92 (SD 61) AU to 132 (SD62) AU. The three parameters, change in maximum intensity, change in intensity rate and relative change in intensity rate were testes using ROC. The best area under curve was achieved with the absolute change in maximum intensity. 19AU increase predicted overall wound healing with 69% sensitivity and 68% specificity (AUC 0.79). 35 AU increase in intensity predicted wound healing in 4 months with 64% sensitivity and 63% specificity (AUC 0.68), 30 AU increase predicted wound healing in 6 months with 69% sensitivity and 69% specificity (AUC 0.72). In patients who underwent EVR the mean maximum intensity increased from 99.7 (SD 60.9) to 127.1 (SD 62.1) in the wound area. The corresponding increase in patients who underwent bypass was from 79.6 (SD60.1) AU to 140 (SD 62.9) AU (p<0.001). One-year wound healing rate after EVR was 84% and after bypass 92%. Conclusion - ICG-FI shows well the success of revascularization in individual patient. In our analysis the best parameter in predicting wound healing was absolute change in maximum intensity. The higher the change is achieved, the faster is the wound healing.