Background It remains elusive which patients with an abdominal aortic aneurysm (AAA) will experience cardiovascular disease progression. Current literature on small AAAs is characterized by hetero-geneous and selective outcome reporting. A core outcome set (COS), a consensus-based list of outcomes that should be reported as a minimum in research on a specific disease, is therefore needed. This is especially important for research using artificial intelligence (AI) techniques. The current study aimed to create a European COS for use in clinical and AI research on small AAAs. This COS will be used in the VASCUL-AID project, which aims to identify risk factors for cardiovascular disease progression in patients with small AAA using AI. Methods This COS was developed in line with Core Outcome Measures in Effectiveness Trials (COMET) initiative recommendations in three steps. First, a longlist of AAA outcomes was identified through a systematic literature search and through focus groups with patients, their caregivers, and healthcare professionals. Second, a three-round European Delphi survey was conducted with patients and a wide range of healthcare professionals. Third, an expert consensus meeting with key opinion leaders (KOL), patients, and patient representatives was held to finalize the COS. Results The AAA longlist consisted of 91 outcomes; 73 outcomes identified from the systematic litera-ture search and 18 patient-centred outcomes identified from the focus groups. A total of 257 participants (of which 104 were patients) participated in the Delphi study. Delphi round 3 was filled in by 221 (66.9%) participants. The highest-rated outcomes from the third Delphi round were included for discussion in the expert consensus meeting, which was attended by 23 KOL, two patients and one patient representative. Ten core outcomes were chosen across six health domains, with AAA rupture, mortality, health-related quality of life, clinical success, and graft infection attaining 100% consensus for inclusion in the COS. Conclusion This first COS for small AAAs consists of ten outcomes and should be implemented in all clinical and AI research on small AAA.
