Abdominal Aortic Aneurysm Growth Profiles Over Time: Prognostic Implications and Biological Insights.

Objective: Progressing abdominal aortic aneurysms (AAA) show a patchwork of rupture-prone wall segments with fast growth and/or greater wall stress, often not located around the maximum diameter. This study aimed to characterize AAA-growth profiles over time and investigate their prognostic value for AAA-progression.

Methods: In this prospective, observational cohort of AAA-patients (maximum diameter ≥40mm) under periodic surveillance, participants underwent blood sampling at baseline and were followed over two years with annual CT-imaging. Aortic diameter was repeatedly measured between the lowermost renal artery and 10mm above the aortic bifurcation at 5% length intervals. The largest diameter change (≥ or < 2.6mm) and its distance from the maximum aneurysm diameter (> or ≤ 10% of aneurysm length) were used to classify patients at one and two years into slow, edge and peak growth. A symmetry test was used to test for directionality of changes in growth profiles between the first and the second year. Secondary outcomes were time-to-surgical threshold, as well as differences in diameter/volume growth and circulating biomarkers, investigated using Cox-, mixed-effects, and linear regression models, respectively.

Results: 92 of 101 patients adhered to one-year imaging [mean age 72 (standard deviation: 6.9), 84 male, median maximum diameter 45 (25^th-75^th percentile: 42, 48) mm]. 55 patients showed edge growth, 20 slow growth and 17 peak growth. 75 of 76 alive, untreated patients underwent two-year imaging, 41 showed edge growth, 12 slow growth and 22 peak growth. Most patients did not change in growth profile over time. Those that did change, went from slow to edge to peak growth (p=0.027). The cumulative incidence (95% confidence interval (CI)) to qualify for surgery in the subsequent year was 0% (0, 0) for patients with slow growth, 23% (12, 36) for edge growth, and 43% (16, 67) for peak growth (slow vs. edge p = 0.029, edge vs. peak p = 0.186). When accounting for differences in maximum diameter, the hazard ratio (95% CI) for qualifying for surgery was 5.24 (1.68, 16.38) for patients showing peak growth, compared to edge growth (p=0.004).

Conclusions: Fast AAA growth predominantly occurs at the edges of the aneurysm, which may shift towards the maximum diameter over time. These growth profiles, alongside maximum aneurysm diameter, may help identify patients that are more or less likely to qualifying for surgery in the short term.