Objective: Aneurysm sac behavior after fenestrated or branched endovascular repair (FB-EVAR) of thoracoabdominal aortic aneurysms (TAAA) remains a key knowledge gap. The purpose of this study was to identify independent predictors of sac behavior after FB-EVAR and assess the relationship between sac behavior and long-term survival.

Methods: Patients undergoing FB-EVAR between 2005 and 2023, in 10 physician-sponsored investigational device exemption studies in the US, were analyzed. Patients who underwent elective FB-EVAR for juxtarenal, suprarenal, or extent 1-5 TAAAs and had 30-day and 1-year CT follow-up imaging were included. Patients with chronic aortic dissections were excluded. Sac regression or expansion (≥5mm) was defined using the Society of Vascular Surgery Guidelines. Independent predictors of sac growth were identified using multivariable logistic regression analysis and survival rates were compared using Kaplan-Meier curves.

Results: Of 3,057 patients who underwent FB-EVAR, 1,497 were eligible for analysis. Median follow-up was 2.9 years (IQR 1.3-4.0). At 1-year, 103 (6.9%) patients experienced sac expansion, while 694 (46.4%) experienced sac regression and 700 (46.7%) had a stable sac. Variables independently associated with sac expansion were age (odds ratio[OR] 1.04; 95% confidence interval[CI] 1.01-1.07; P=0.0057), prior aortic surgery (OR 2.22;CI 1.32-3.40; P=0.0026), prior EVAR (OR 1.84;CI 1.07-3.14; P=0.0264), larger aneurysm diameter (OR 1.03; CI 1.01-1.04; P=0.0014), type 2 endoleak observed on 30-day follow-up CT (OR 2.15; CI 1.36-3.41; P=0.0011), and any secondary intervention during the first year (OR 2.19; CI 1.35-3.55; P=0.0016). Overall survival at 1 year was significantly lower in the expansion group compared to the stable and regression groups (85.6% vs 90.9% vs 93.1%, respectively). This effect persisted on 5-year evaluation (48.1% vs 63.0% vs 67.7%, respectively). Both expansion and stability at 1 year were both associated with increased long-term mortality in unadjusted cox model (expansion: hazard ratio [HR] 2.083, CI 1.47-2.95, P<0.0001; stability: HR 1.26; CI 1.02-1.56, P=0.0298) versus regression.

Conclusions: Both aneurysm sac expansion and stability (lack of regression) one year after FB-EVAR are associated with decreased long-term survival compared to sac regression. These outcomes underscore the need for vigilant monitoring of patients without sac regression and to better understand if interventions to address factors associated with unfavorable aneurysm sac behavior can improve long term survival.