Risk Scores for the Loss of Secondary Patency and Major Amputation After Successful Thrombectomy of an Infra-inguinal Arterial Bypass.

BACKGROUND: The purpose of this study was to utilize Vascular Quality Initiative (VQI) data to create internally validated risk scores for two primary outcome events of loss of secondary patency and major lower extremity amputation after successful thrombectomy of infra-inguinal arterial bypasses. The goal is to identify modifiable variables which can improve outcomes after successfully recanalizing an occluded infra-inguinal arterial bypass.

METHODS: Variables with a multivariable P value ≤0.05 for the outcomes were included in the risk scores and weighted based on their respective regression beta-coefficient in a point scale. Multivariable significant factors with a beta-coefficient of less than 0.25 were assigned 1 point, and then a point was added for each rise in beta-coefficient at 0.25 intervals. A cumulative score was then created for each patient by adding up the points assigned for each significant multivariable factor they possessed. Risk scores were then bundled into groups to allow for cohesion, simplification, enhancement of statistical power, and reduced random effects of smaller sample sizes for a given risk score. Area under curve (AUC) analysis was performed for the risk scores in determining the accuracy of association with loss of secondary patency and major amputation.

RESULTS: Variables with a statistically significant (P < 0.05) multivariable association with amputation were as follows: female sex (aOR 1.39); living in a top 20% area deprivation index neighborhood (aOR 1.84); body mass index (BMI) <20 kg/m2 (aOR 1.84); multiracial designation (aOR 2.29 relative to white reference); diabetes requiring oral hypoglycemics (aOR 1.86) or insulin (aOR 2.97); anemia (aOR 1.69); tibial/pedal bypass target (aOR 2.93); being selected for anticoagulant at time of initial hospital discharge (aOR 1.61); lack of surveillance imaging in follow-up (aOR 2.93); smoking at long-term follow-up (LTFU, aOR 104.4) and smoking status unknown relative to nonsmokers (aOR 24.2); nonambulatory status at LTFU (aOR 10.50); and re-occluded bypass at LFTU (aOR 2.81). Variables which were protective (P < 0.05) from amputation on multivariable analysis were being on anticoagulation at the time of LTFU (aOR 0.67); prior aneurysm repair (aOR 0.42); and BMI >35 (aOR 0.53). There was noted to be steep escalation in the frequency of major amputation with rising risk score. At one extreme, no patients with scores ≤ 15 experienced amputation and at the other extreme, 77.8% of the patients with scores of over 37 suffered amputation. There was a statistically significant (P < 0.01) rise in amputation rate at each rising risk score bundle. There was an essentially identical rate of amputation in the testing and validation at all risk score bundles with no significant difference in amputation rate at any of the risk score bundles. AUC analysis for the testing cohort achieved a value of 0.881 for the amputation testing cohort and 0.896 for the validation cohort. For the loss of secondary patency risk score, again a significant rise in outcome event was noted with rising risk score bundle with patients with scores of 6 and higher experiencing event at over 4 times a higher rate than those with scores less than -2.

CONCLUSION: Internally validated risk calculators with steep escalation in event rates with progressive scores have been created for the outcomes of major amputation and loss of secondary patency after successful recanalization of an infra-inguinal arterial bypass. Key patient and physician-driven modifiable variables in preventing adverse outcomes include smoking cessation, bypass surveillance imaging compliance, single segment vein utilization at original operation, and administration of anticoagulant and antiplatelet medications.