Predictive ability of the Society for Vascular Surgery Wound, Ischemia, and foot Infection (WIfI) classification system after first-time lower extremity revascularizations

Objective: The Society for Vascular Surgery (SVS) Wound, Ischemia and foot Infection (WIfI) classification system was proposed to predict 1-year amputation risk and potential benefit from revascularization. Our goal was to evaluate the predictive ability of this scale in a real-world selection of patients undergoing a first-time lower extremity revascularization for chronic limb-threatening ischemia (CLTI).
Methods: From 2005 to 2014, 1336 limbs underwent a first-time lower extremity revascularization for CLTI, of which 992 had sufficient data to classify all three WIfI components (wound, ischemia, and foot infection). Limbs were stratified into the SVS WIfI clinical stages (from 1 to 4) for 1-year amputation risk estimation, a novel WIfI composite score from 0 to 9 (that weighs all WIfI variables equally), and a novel WIfI mean score from 0 to 3 (that can incorporate limbs missing any of the three WIfI components). Outcomes included major amputation; revascularization, major amputation, or stenosis (>3.5× step-up by duplex; RAS) events; and death. Predictors were identified using Cox regression models and Kaplan-Meier survival estimates.
Results: Of the 1336 first-time procedures performed, 992 limbs were classified in all three WIfI components (524 endovascular and 468 bypass; 26% rest pain and 74% tissue loss). Cox regression demonstrated that a one-unit increase in the WIfI clinical stage increases the risk of major amputation (hazard ratio [HR], 2.4; 95% confidence interval [CI], 1.7-3.2) and RAS events in all limbs (HR, 1.2; 95% CI, 1.1-1.3). Separate models of the entire cohort, a bypass-only cohort, and an endovascular-only cohort showed that a one-unit increase in the WIfI mean score is associated with an increase in the risk of major amputation (all three cohorts: HR, 5.3 [95% CI, 3.6-6.8], 4.1 [2.4-6.9], and 6.6 [3.8-11.6], respectively) and RAS events (all three cohorts: HR, 1.7 [95% CI, 1.4-2.0], 1.9 [1.4-2.6], and 1.4 [1.1-1.9], respectively). The novel WIfI composite and WIfI mean scores were the only consistent predictors of death among the three cohorts, with the WIfI mean score proving most strongly predictive in the entire cohort (HR, 1.4; 95% CI, 1.1-1.7), the bypass-only cohort (HR, 1.5; 95% CI, 1.1-1.9), and the endovascular-only cohort (HR, 1.4; 95% CI, 1.0-1.8). Although the individual WIfI wound component was able to predict mortality among all patients (HR, 1.1; 95% CI, 1.0-1.2) and bypass-only patients (HR, 1.2; 95% CI, 1.1-1.3), neither the additional individual WIfI components nor the WIfI clinical stage were able to significantly predict mortality among any cohort.
Conclusions: This study supports the ability of the SVS WIfI classification system to predict major amputation; however, the novel WIfI mean and WIfI composite scores predict amputation, RAS events, and mortality more consistently than any other current WIfI scoring system. The WIfI mean score allows inclusion of all limbs, and both novel scoring systems are easier to conceptualize, give equal weight to each WIfI component, and may provide clinicians more effective comparisons in outcomes between patients.