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Lower Extremity Bypass is Associated with Lower Short-Term Major Adverse Limb Events and Equivalent Major Adverse Cardiac Events Compared to Endovascular Intervention in A National Cohort with Critical Limb Ischemia
James H Mehaffey, Robert Hawkins, Anna Fashandi, Margret C Tracci, Kenneth Cherry, Irving Kron, Gilbert Upchurch, William P Robinson
UVA, Charlottesville, VA

Background
Lower extremity bypass (LEB) has traditionally been the gold standard in the treatment of critical limb ischemia (CLI). Over the past two decades, infrainguinal endovascular intervention (EI) has gained widespread acceptance and is now more commonly performed than LEB. Intuitively, EI should have the advantage of lower procedural risk in the complex critical limb population with multiple medical comorbidities. However, data directly comparing LEB and EI remains sparse. In addition, in many studies the heterogeineity of patients included and procedures performed along with a lack of standardization in the outcomes reported have rendered careful comparison of LEB and EI for CLI difficult.
The Society for Vascular Surgery (SVS) Objective Performance Goals (OPGs) provide standardized metrics for expected outcomes after lower extremity revascularization which allow for comparison of LEB and EI in the CLI population. Included among the most important OPG outcomes are Major Adverse Limb Events (MALE) and Major Adverse Cardiovascular Events (MACE). There is very little data examining MALE and MACE after EI. Furthermore, there are no direct comparisons of LEB and EI utilizing these important endpoints.
The National Surgical Quality Improvement Program (NSQIP) provides a national sampling of cases with complete 30-day follow-up. The recently developed Vascular Targeted modules have been added to the existing annual participant use file (PUF) since 2011, providing additional vascular specific variables and outcomes including limb and cardiovascular events. The primary purpose of this study was to compare rates of MALE and MACE after LEB and EI in a propensity-matched, national cohort of patients with CLI.
Methods
The NSQIP Vascular Targeted PUF (2011-2014) for both lower extremity open and lower extremity endovascular were merged to obtain a representative national dataset. Details on the accruement methods and validity of the ACS-NSQIP have been documented. CLI patients were defined as having an indication of ischemic rest pain and/or tissue loss for revascularization. To account for potential confounders, specifically nonrandom allocation to LEB or EI, we matched patients on a 1:1 basis for propensity to undergo LEB or EI.
Appropriate parametric and nonparametric statistical tests were used to compare LEB and EI. The primary outcomes were MALE and MACE within 30 days. MALE was defined as either untreated loss of patency of the revascularization, re-intervention on the revascularization, or major amputation of the revascularized limb. MACE was definded as stroke, myocardial infarction (MI), or death. Secondary outcomes included untreated loss of patency of the revascularization, re-intervention on the revascularization, major amputation, stroke, myocardial infarction (MI), and death. Within the propensity matched cohort multivariate logistic regression was then used to identify independent predictors of MALE and MACE. Statistical significance was set to an α of 0.05. All statistical analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC).
Results
A total of 13,294 LEB and EI were identified in the 2011-2014 NSQIP Vascular Targeted modules. There were 8,066 cases perfomed for CLI defined as rest pain or tissue loss. All procedures for claudication or asymptomatic peripheral vascular disease, as well as emergencies were excluded. After propensity matching for LEB versus EI was performed 3,848 cases (1,924 LEB and 1,924 EI) were left for analysis. The median age of our matched cohort was 69 and 58.8% were male. There were no differences in preoperative variables between the propensity matched LEB and EI groups (all p>0.05).
At 30 days, MALE was significantly lower in the LEB group (9.2% LEB vs 12.2% EI, p=0.003). This was driven primarily by a significantly higher rate of amputation in the EI group (4.2% LEB vs 6.8% EI, p=0.0003). However, there was a higher rate of untreated loss of patency in the LEB group (2.7% LEB vs 1.7% EI, p=0.03) with no difference in reintervention (4.8% LEB vs 5.5% EI, p=0.38). On multivariate logistic regression, independent predictors of MALE included tibial bypass/tibial intervention (OR 1.4, p=0.01) and a history of prior bypass of currently revscularized segment (OR1.8, p<0.0001). Antiplatelet therapy (OR 0.8, p=0.049), statin therapy (OR 0.8, p=0.04), bypass with single segment saphenous vein vs. EI (OR 0.7, p=0.01), and bypass with alternative conduit (prosthetic/spliced vein/composite) vs. EI (OR 0.7, p=0.04) were protective against MALE.
A logistic model was also created for 30-day ipsilateral major amputation since it was the driving component for MALE outcomes. Independent predictors of amputation included black race (OR 1.6, p=0.003), dialysis dependence (OR 1.8, p=0.001), and prior bypass of current segment (OR1.8, p=0.001). Antiplatelet therapy (OR 0.7, p=0.049), and bypass with single segment saphenous vein vs EI (OR 0.5, p=0.001) were protective against amputation.
MACE at 30 days was not significantly different (4.9% LEB vs 3.7% EI, p=0.07) between the groups. Similarly rates of MI/CVA (2.8% LEB vs 2.1% EI, p=0.14) and 30-day mortality (2.9% LEB vs 2.1% EI, p=0.15) were not different between groups. On multivariate logistic regression independent predictors of 30-day MACE included age (OR 1.02, p=0.01), steroid use (OR 1.8, p=0.03), congestive heart failure (OR 1.7, p=0.02), beta-blocker use (OR 1.6, p=0.01), dialysis dependence (OR 2.3, p<0.0001), totally dependent functional status (OR 3.1, p=0.02), and suboptimal conduit for LEB compared to EI (OR 1.6, p=0.02).
Conclusions
Within this large, propensity-matched, national cohort, lower extremity bypass was associated with lower 30-day MALE compared to endovascular intervention. The increased MALE was driven by a higher rate of amputation in the EI group. Further risk adjustment with multivariate regression demonstrates that both optimal conduit (single segment saphenous vein) and suboptimal conduit (prosthetic/spliced vein/composite) independently reduce the risk of MALE compared to the EI approach. Other important predictors of decreased MALE are antiplatelet therapy and statin therapy, highlighting the importance of optimal medical management preoperatively. Factors identified that independently increase the risk of MALE include revascularization of infrageniculate targets, which are typically smaller with higher risk of failure, and prior bypass of the currently treated segment, demonstrating the poor prognosis for redo interventions. Since amputation was the driving factor for MALE outcomes, a multivariate regression was also modeled for these outcomes with many similar predictors of reduced amputation including antiplatelet therapy and optimal conduit compared to EI. Multivariate modeling did not have excellent discriminatory power to accurately predict MALE or amputation, indicating other factors, such as vascular anatomy, likely have an important impact on these outcomes.
Despite the higher risk inherent in open operations requiring general anesthesia, we found no statistical difference in MACE or either component outcome with LEB compared to EI. After further adjusting for preoperative risk factors with multivariate logistic regression, suboptimal conduit versus EI approach was the only revascularization-specific predictor of MACE. Other predictors were expected and included age, congestive heart failure, dialysis, steroid use, totally dependent functional status, and beta-blocker use.
Using the NSQIP Vascular Targeted modules over the past four years, this analysis demonstrates improved risk-adjusted rates of 30-day MALE with LEB compared to EI in the management of CLI. The present study supports LEB as the optimal therapy in the management of CLI. Our propensity matched national cohort analysis demonstrates the need for further investigation into identifying patients who are most appropriate for LEB or EI. Additionally, these results highlight the need for a randomized controlled trial of LEB compared to EI for the treatment of CLI.
This dataset demonstrates poor national performance compared to the 30-day safety thresholds (8% MACE, 8% MALE, 3% amputation) for CLI previously established by OPGs based on clinical trial data. Although MALE and amputation rates are above the safety threshold for both LEB and EI, we found MACE performance is within acceptable range for both approaches. While new techniques must be evaluated with clinical trials in high volume centers of excellence, it is critical to assure safety thresholds are maintained with widespread adoption of these techniques. The results of this study necessitate further investigation into national practice patterns in the management of CLI with LEB and EI.


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