Prediction of Long-term Change in Post-EVAR Aneurysm Sac Size

BACKGROUND: Shrinkage of abdominal aortic aneurysms after endovascular treatment has been found to be related to pre-operative aneurysm size, endoleak and device type in previous studies with intermediate-term (up to 24 months) results. This study analyzes long-term sac size change and aneurysm retraction in patients who were treated with the Zenith^® AAA Endovascular Graft in a large prospective multicenter study with follow-up results through 5 years.
METHODS: Patients were categorized into 3 groups by maximum major aneurysm diameter: small (<55 mm), medium (≥55 mm and <65 mm) and large (≥65 mm). Each group was further divided by the absence or presence of any type of endoleak, detected by the core laboratory from CT images at any time during the study. Aneurysm size data were used to construct a nonlinear mixed model to predict sac size change over time. Complete aneurysm retraction, defined as shrinkage of the aneurysm to the mean graft diameter plus 10 mm (5 mm of residual thrombus on either side of the graft), was also analyzed.
RESULTS: Of 733 endovascular patients included in this analysis, 575 patients received 2-year follow-up (mean 21.7 months) and 158 patients received 5-year follow-up (mean 60.2 months). Patients with large (L, n=121), medium (M, n=263) and small (S, n=349) baseline aneurysms exhibited similar pre-operative demographics and co-morbidities except for age (patients with larger aneurysms were older, P=0.0014). The nonlinear mixed model (Figure 1) showed significant effects (P<0.0001) of baseline aneurysm size and endoleak on sac behavior. In patients without endoleak, the predicted mean decrease in sac size over 5 years and relative change (%) from the baseline were 25.1 mm (36.2%), 19.1 mm (32.5%) and 11.4 mm (22.9%) for L, M and S groups, respectively. The decrease was much less for patients with endoleak: 14.1 mm (20.4%), 9.3 mm (15.8%) and 1.9 mm (3.8%) for L, M and S groups, respectively (P<0.0001). Complete aneurysm retraction was observed in 86 patients (Table 1). The Kaplan-Meier estimate of retraction was 14.8% at 2 years and 42.4% at 5 years. Complete retraction was predicted at 5.1 and 5.5 years for endoleak-free patients in the S and M groups, respectively; however, within the examined time frame, no complete retraction was predicted for patients with endoleak or with large baseline aneurysms (Figure 1).
CONCLUSIONS: This analysis of a large, prospective patient population with long-term follow-up supports previous findings that aneurysms of larger baseline sizes tend to shrink with a greater rate over time. Presence of endoleak significantly reduces the rate of shrinkage of aneurysms of all sizes. Complete retraction is only predicted for aneurysms of medium and small sizes within 6 years in the absence of endoleak.