Establishing a Predictive Perfusion Threshold Using SPY-PHI QP in Staged Breast Reconstruction: A Prospective Evaluation With Nitroglycerin Adjustment.

Abstract

The SPY Fluorescence Imaging system enables intraoperative visualization of microvascular perfusion. Recently, SPY has been integrated with Quantitative Perfusion (QP) software to provide numerical assessment of relative tissue perfusion; however, clinically actionable perfusion thresholds predictive of mastectomy skin necrosis complications have not been clearly established. To evaluate the predictive performance of proposed SPY-PHI QP perfusion thresholds in patients undergoing staged breast reconstruction and to explore a QP-specific cutoff while accounting for nitroglycerin ointment use as a potential confounder. Patients undergoing staged breast reconstruction with tissue expander placement were included. SPY-PHI QP was used intraoperatively to assess relative perfusion. Diagnostic performance metrics-including sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and odds ratios-were calculated. A sub-analysis excluding patients who received nitroglycerin ointment was performed to identify a QP-specific cutoff in unmanipulated tissue. Fifty-eight patients (83 breasts) were included. Using a 33% perfusion threshold, SPY-PHI QP® demonstrated high sensitivity (87.5%) and negative predictive value (98.3%) for mastectomy skin flap necrosis. After adjusting for nitroglycerin use, the association between low perfusion and mastectomy skin flap necrosis was attenuated. In patients who did not receive nitroglycerin, a perfusion threshold of 30% demonstrated optimal diagnostic performance (sensitivity 100%, specificity 76.7%, AUC 0.8875). SPY-PHI QP provides quantitative, real-time assessment of tissue perfusion during breast reconstruction. In patients not treated with nitroglycerin, a 30% perfusion threshold may be predictive of wound complications. These findings support further investigation of QP-specific thresholds in larger, prospective studies that account for adjunctive interventions.