Ingress Time as a Metric for Indocyanine Green Angiographic Evaluation of Skin Flap Perfusion in Immediate Implant-Based Reconstruction

BACKGROUND: Rapid ingress is a hallmark of normal flap perfusion in indocyanine green (ICG) angiography. This study aimed to assess whether the ingress time in ICG angiography can be used to evaluate mastectomy skin flap (MSF) perfusion in immediate implant-based breast reconstruction (IBR). METHODS: Consecutive patients who underwent immediate IBR with intraoperative ICG angiography between June of 2021 and December of 2022 were retrospectively reviewed. ICG angiography was performed for 120 seconds after temporary skin closure. The ingress time, defined as the time (in seconds) for ICG to perfuse the entire MSF, including incision margins, was recorded. The primary outcome measured was the development of full-thickness MSF necrosis. A receiver operating characteristic curve and an F1 score based on the precision-recall curve analysis were used to determine the optimal ingress time cutoff value for predicting full-thickness necrosis of MSF. RESULTS: The study included 203 breasts from 203 patients. Full-thickness necrosis of MSF developed in 33 patients (16.3%). The mean ingress times in the necrosis and no-necrosis groups were 104.6 seconds and 47.6 seconds, respectively ( P < 0.001). In receiver operating characteristic and precision-recall curve analyses, the optimal cutoff value was 70.5 seconds, yielding a sensitivity of 82%, specificity of 84%, and accuracy of 83%. In multivariable analysis, an ingress time of 70.5 seconds or longer was a significant predictor of full-thickness necrosis of MSF (OR, 26.79; P < 0.001). CONCLUSION: An ingress time in ICG angiography may serve as a novel metric for evaluation of MSF perfusion. CLINICAL QUESTION/LEVEL OF EVIDENCE: Diagnostic, IV.