Objective: Patients undergoing revascularization for chronic limb-threatening ischemia (CLTI) are at elevated risk for both mortality and limb loss. To facilitate therapeutic decision-making, a mortality prediction model derived from the Vascular Quality Initiative (VQI) database has stratified patients into low, medium, and high risk, defined by 30-day mortality estimates of ≤3%, 3%-5%, or >5% and 2-year mortality estimates of ≤30%, 30%-50%, or ≥50%, respectively. The purpose of this study was to compare expected mortality risk derived from this model with observed outcomes in a tertiary center.
Methods: Consecutive patients treated at a single center between 2016 and 2019 were analyzed. Baseline demographics, approach, and mortality events were reviewed. Observed mortality was obtained using life-table methods and compared using a log-rank test with the expected mortality risk that was calculated using the VQI model.
Results: This study cohort consisted of 195 revascularization procedures in 169 unique patients stratified into 128 (66%) low-, 50 (26%) medium-, and 17 (8%) high-risk cases based on the VQI model. Ninety percent of revascularizations were performed for tissue loss. Compared with the VQI population, comorbidities were prevalent and included unstable angina or myocardial infarction within 6 months (6% vs 2.4% in VQI; P < .001), congestive heart failure (30% vs 23%; P < .001), and dialysis dependence (14% vs 0.9%; P < .001). Patients were also older (31% vs 21% ≥80 years old; P < .001) and more likely to be frail (45% vs 64% independent; P < .001). High-risk patients were more prevalent in the endovascular group (11% of 132 endovascular interventions vs 3% of 63 bypasses; P = .056). Thirty-day observed mortality exceeded expected VQI prediction model mortality in all groups, although was not statistically significant. The VQI model adequately stratified the studied population into risk groups (P < .001). Low-risk patients with CLTI (65% of the overall cohort) experienced 2-year mortality of 18.9%. However, observed mortality rates for medium- and high-risk VQI strata were similar. After a median follow-up of 28 months, medium-risk patients incurred a significantly higher mortality than predicted (53.5% ± 2.1% vs 36.8% ± 1.1%; P = .016).
Conclusions: The VQI mortality prediction model discriminates mortality risk after limb revascularization in CLTI, accurately identifying a majority subgroup of patients who are suitable for either open or endovascular intervention. However, it may underestimate mortality in a tertiary referral population with high comorbidity burden and was not well calibrated for the medium-risk group. It may be more appropriate to dichotomize patients with CLTI who are candidates for limb salvage into an average-risk and high-risk group.
Keywords: Calibration; Infrainguinal revascularization; Mortality; VQI.
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