Validation of the PIII CLI risk score for the prediction of amputation-free survival in patients undergoing infrainguinal autogenous vein bypass for critical limb ischemia
Presented at the 2009 Vascular Annual Meeting, Denver, Colo, June 11-14, 2009.
Received 4 May 2009; accepted 28 May 2009. published online 23 July 2009.
Objective
The PREVENT III (PIII) critical limb ischemia (CLI) risk score is a simple, published tool derived from the PIII randomized clinical trial that can be used for estimating amputation-free survival (AFS) in CLI patients considered for infrainguinal bypass (IB). The current study sought to validate this risk stratification model using data from the prospectively collected Vascular Study Group of Northern New England (VSGNNE).
Method
We calculated the PIII CLI risk score for 1166 patients undergoing IB with autogenous vein by 59 surgeons at 11 hospitals between January 1, 2003, and December 31, 2007. Points (pts) were assigned to each patient for the presence of dialysis (4 pts), tissue loss (3 pts), age ≥75 (2 pts), and coronary artery disease (CAD) (1 pt). Baseline hematocrit was not included due to a large proportion of missing values. Total scores were used to stratify each patient into low-risk (≤3 pts), med-risk (4-7 pts), and high-risk (≥8 pts) categories. The Kaplan-Meier method was used to calculate AFS for the three risk groups. Log-rank test was used for intergroup comparisons. To assess validation, comparison to the PIII derivation and validation sets was performed.
Result
Stratification of the VSGNNE patients by risk category yielded three significantly different estimates for 1-year AFS (86.4%, 74.0%, and 56.1%, for low-, med-, and high-risk groups). Intergroup comparison demonstrated precise discrimination (P < .0001). For a given risk category (low, med, or high), the 1-year AFS estimates in the VSGNNE dataset were consistent with those observed in the previously published PIII derivation set (85.9%, 73.0%, and 44.6%, respectively), PIII validation set (87.7%, 63.7%, and 45.0%, respectively), and retrospective multicenter validation set (86.3%, 70.1%, and 47.8%, respectively).
Conclusion
The PIII CLI risk score has now been both internally and externally validated by testing it against the outcomes of 3286 CLI patients who underwent autogenous vein bypass at 94 institutions by a diverse array of physicians (three independent cohorts of patients). This tool provides a simple and reliable method to risk stratify CLI patients being considered for IB. At initial consultation, calculation of the PIII CLI risk score can reliably stratify patients according to their risk of death or major amputation at 1 year.
aUniversity of Massachusetts Medical School, Worcester, Mass
cUniversity of California San Francisco, San Francisco, Calif
Reprint requests: Andres Schanzer, MD, Division of Vascular and Endovascular Surgery, University of Massachusetts Memorial Medical Center, 55 Lake Ave North, Worcester, MA 01655
ABSTRACT