Quantitative Assessment of Indocyanine Green Angiography in the Follow-Up of Patients with Severe Chronic Limb Ischaemia

Abstract

Introduction - An ischaemic wound heals slowly after revascularization, and repeated revascularizations are needed in many cases to avoid amputation. Therefore, a surveillance programme is recommended to ensure revascularization patency and to prevent the need for additional procedures using the ankle-brachial index (ABI) and the toes (TP). Indocyanine green fluorescence imaging (ICG-FI) is useful to evaluate the perfusion of an ischaemic foot. The aim of this study was to assess the feasibility of ICG-FI in the surveillance of patients who have undergone revascularization of severe chronic limb ischemia (SCLI). We sought to determine the sensitivity and specificity of ICG-FI in distinguishing possible revascularization failure after bypass or PTA, as compared to ABI and TP. Methods - In this prospective trial, 61 patients (62 limbs) with SCLI were examined with ABI, TP and ICG-FI at baseline, immediately after revascularization and at 3-month follow-up. Twenty-five patients (33%) underwent bypass, and 36 (67%) underwent a total of 37 PTAs. ICG-FI results were assessed with the SPY-Q software, which provides a time-intensity curve of the selected region of interest (ROI), showing the fluorescence intensity plotted against time in seconds. Three parameters were derived from the curve: maximum intensity, intensity rate (IU/S), and ICG10 (intensity achieved during the first 10 seconds). Two ROIs were selected: the dorsum of the foot and the plantar region. ICG-FI results were compared with ABI and TP. The clinical status of the foot was analysed as to whether the wound was healed, healing, similar or worse. Results - At 3-month follow-up, the clinical status was improved compared to the baseline in 39 legs (63%); the wound was completely healed or healing), but in 23 (37%), the wound status was unchanged or worse. The sensitivity and specificity of ICG-FI for the unchanged or deteriorated clinical status were 61% and 72%, respectively. In 23 cases, the clinical status had not improved and ultrasound examination revealed restenosis or occlusion in 20 (90%) patients, and a new revascularization was scheduled. In 100% of these cases, ICG-FI at follow-up showed worse results compared to the immediate postoperative ICG-FI. A reliable ABI was possible in 38 (61%) legs at the follow-up visit, and it was higher than the baseline ABI in 29 (76%) cases and unchanged/worse in 9 (24%). The sensitivity and specificity to detect a deteriorated situation were 91% and 47%, respectively. TP measurements were possible in 49 (79%) cases at the follow-up visit. For 34 (69%) cases, the TP had increased from the baseline, while 15 (31%) had worse or unchanged values. The sensitivity to detect unfavourable healing was 80%, with a specificity of 47%. In ROC, the areas under the curve (AUC) using ICG-FI, ABI and TP were 0.66 (95% CI 0.52-0.81, p=0.03), 0.69 (95% CI 0.51-0.87, p=0.05) and 0.64 (95% CI 0.47-0.80, p=0.11), respectively. ICG-FI correlated with the clinical status in 68% of the cases, as opposed to the 74% correlation achieved with ABI and 67% with TP when only cases with successful measurements were considered. However, when all patients were considered, the respective proportions for ABI and TP were only 45% and 53%, due to the fact that not all patients had ABI and TP measurements available. Conclusion - ICG-FI is useful and feasible in the surveillance of SCLI after revascularization. Unlike ABI and TP, it can be measured in all patients. ReferencesSettembre N et al. World J Surg 2017,6