Predictive Ability of SVS WIfI Classification System Studied in First-Time Lower Extremity Revascularizations

 

March 22, 2017—Marc L. Schermerhorn, MD, led an investigation of the predictive ability of the Society for Vascular Surgery (SVS) Wound, Ischemia, and foot Infection (WIfI) classification system after first-time lower extremity revascularizations. The findings were published by Jeremy D. Darling, BA, et al in Journal of Vascular Surgery (JVS; 2017;65:695–704).

According to the investigators, the SVS WIfI classification system was proposed to predict 1-year amputation risk and potential benefit from revascularization. The goal of this study 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).

As summarized in JVS, the investigators identified 1,336 limbs that underwent a first-time lower extremity revascularization for CLTI from 2005 to 2014. Of these, 992 limbs had sufficient data to classify all three WIfI components (wound, ischemia, and foot infection). There were 524 limbs treated by endovascular procedures and 468 limbs treated by bypass surgery with 26% experiencing rest pain and 74% with tissue loss. 

Limbs were stratified into the SVS WIfI clinical stages (1–4) for 1-year amputation risk estimation, a novel WIfI composite score (0–9) weighs all WIfI variables equally, and a novel WIfI mean score (0–3) incorporates limbs missing any of the three WIfI components. Outcomes included major amputation; revascularization, major amputation, or stenosis (> 3.5 X step-up by duplex; renal artery stenosis [RAS]); and death. Predictors were identified using Cox regression models and Kaplan-Meier survival estimates.

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]; 1.9 [1.4–2.6]; and 1.4 [1.1–1.9], respectively). 

According to the investigators, 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 to be the 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, 1–1.8). Although the individual WIfI wound component was able to predict mortality among all patients (HR, 1.1; 95% CI, 1–1.2) 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.

The investigators concluded that the 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, advised the investigators in JVS.

 

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