As the sac grows, the window closes: Aneurysm size, IFU compliance, and outcomes after endovascular aneurysm repair

Aim: Current guidelines recommend endovascular aneurysm repair (EVAR) for infrarenal abdominal aortic aneurysm (iAAA) at a ≥ 55 mm threshold, based primarily on rupture risk. Whether sac diameter and instructions-for-use (IFU) compliance independently influence outcomes remains unclear. We examined how sac size relates to neck anatomy, IFU compliance, and long-term outcomes.

Material and Methods: In this single-centre retrospective study, 383 of 435 consecutive patients undergoing elective EVAR (January 2016-January 2026) were analysed. ROC-derived cut-offs stratified patients into small (≤ 55 mm), medium (56 – 64 mm), and large (≥ 65 mm) groups. IFU compliance was assessed against device anatomical criteria. Late mortality, endoleak, and secondary intervention were analysed with Kaplan-Meier and univariable/multivariable Cox regression, with sac size and IFU compliance as covariates.

Results: The cohort was 92.9% male (median age 72). Non-IFU treatment increased with sac size (49.5% small, 60.4% medium, 80.6% large; p < 0.001), paralleling progressive neck deterioration (widening alpha angle, shortening neck, increasing thrombus; all p < 0.001). Non-IFU patients had more Type I endoleaks (14.9% vs 3.7%, p = 0.001) and secondary intervention (19.3% vs 6.0%, p = 0.001), whereas late mortality was similar (22.5% vs 23.9%, p = 0.75). In multivariable analysis, IFU non-compliance was the only independent predictor of secondary intervention (HR 2.91, 95% CI 1.34 – 6.29, p = 0.007), while large sac size independently predicted late mortality (HR 1.75, 95% CI 1.02 – 3.28, p = 0.050).

Conclusion: Sac enlargement progressively compromises proximal neck anatomy and reduces the feasibility of IFU-compliant EVAR. IFU non-compliance drives reintervention, whereas large sac size predicts late mortality. Beyond its rupture-risk role, the ≤ 55 mm threshold may also represent an important anatomical window for IFU-compliant EVAR.