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A Time Based Risk Model to Screen Post EVAR Patients
Chien Yi M. Png, Rami O. Tadros, MD, Peter L. Faries, Sung Yup Kim, William Beckerman, Marielle Torres, Michael Marin.
Icahn School of Medicine at Mount Sinai, New York, NY, USA.

OBJECTIVES:
Follow up computed tomography angiography (CTA) scans add considerable post implantation costs to endovascular aneurysm repairs (EVAR) of abdominal aortic aneurysms (AAA). By building a risk model, we hope to identify patients at low risk for postoperative complications in order to minimize unnecessary CT scans.
METHODS:
557 consecutive patients were reviewed. Probit models were created for four outcomes: aneurysm sac enlargement, reintervention, type I/III endoleaks and type II endoleaks, using preoperative aneurysm morphology, patient demographics and operative details as covariates. Patients with an abnormal 30 day post operative CT scan were excluded. Time points chosen for analysis were 1-year, 2-year, 3-years and 10-year post EVAR. A combined model including three outcomes was also created.
RESULTS:
Individual models that showed most significance were aneurysm sac enlargement at 1-year post EVAR (n=411; Sensitivity=1; Specificity=0.47; Accuracy 0.48) and reintervention at 2-year post EVAR (n=494; Sensitivity=1; Specificity=0.42; Accuracy=0.45). (Table 1) Notably, our models reported that increasing iliac artery diameter and increasing aortic neck angle increased the risk for a reintervention, while increasing iliac artery tortuosity increased the risk for a type I/III endoleak. Similarly, almost all statistically significant covariates were qualitatively supported by prior literature. Our final combined model would prevent the need for post-EVAR CTA in 59 patients (16%) at 1 year, 26 patients (7%) at 2 years and 6 patients (2%) at 3 years. (Table 2)
CONCLUSIONS:
Our model is a robust predictor of patients at low risk for post AAA EVAR complications. With additional validation and refinement, it could be applied to practices to cut down on the overall need for post-implantation CTA. Reducing the number of CT scans will reduce post-implantation cost and radiation exposure.
Table 1: Individual Model Analysis
Model1 year (Aneurysm Sac Enlargement)2 year (Aneurysm Sac Enlargement)1 year (Reintervention)2 year (Reintervention)1 year (Type I/III Endoleak)2 year (Type I/III Endoleak)1 year (Type II Endoleak)2 year (Type II Endoleak)
n411411494494505505470470
True Positive11161826451924
False Positive212278288273123194415412
True Negative1881171881953783063634
False Negative00000000
Sensivity11111111
Specificity0.470.300.400.420.750.610.080.08
Accuracy0.480.320.420.450.760.620.120.12

Table 2: Combined Model Analysis
Combined Model (n=377)1 year (%)2 year (%)3 year (%)
True Positive243550
False Positive294316321
True Negative59266
False Negative000
Sensitivity111
Specificity0.160.070.02
Accuracy0.220.160.15


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