Aortic Size and Height Indices in Abdominal Aortic Aneurysms (AASI)

This is a prospective, observational, international, multicenter study with a case-control analytical design and 30-day mortality follow-up. Participants will be recruited consecutively from participating centers. Patients presenting with ruptured infrarenal abdominal aortic aneurysms will constitute the case group, regardless of whether repair is subsequently performed. Patients with intact infrarenal abdominal aortic aneurysms undergoing open surgical or endovascular repair will constitute the comparison group. No experimental intervention or treatment assignment will occur, and study procedures will not delay or interfere with emergency care.

Each participant will contribute one baseline aneurysm measurement obtained from the index computed tomography (CT) scan performed before surgical or endovascular intervention. Maximum aneurysm diameter will be measured in millimeters from outer wall to outer wall and perpendicular to the vessel centerline using multiplanar reconstruction. The measurement will be performed by a trained observer at the participating center and recorded without rounding.

Height and weight will be selected according to a prespecified measurement hierarchy. The source and date of each anthropometric value, its interval relative to the index CT scan, and whether weight was obtained before intravenous fluid or blood product administration for hemodynamic stabilization will be recorded. Post-resuscitation and postoperative weight will not be used. Body surface area will be calculated using the Du Bois formula. The Aortic Size Index will be calculated as maximum aneurysm diameter in centimeters divided by body surface area in square meters. The Aortic Height Index will be calculated as maximum aneurysm diameter in centimeters divided by height in meters.

A standardized quality-assurance process will be used across participating centers. One de-identified CT study will be randomly selected from each consecutive group of 50 enrolled participants for independent remeasurement by a designated reviewer at the coordinating center. The central reviewer will be blinded to the original local measurement. Both measurements will be retained for quality-control analysis, but the central measurement will not replace the original analytical measurement.

Study data will be entered into a centralized Research Electronic Data Capture (REDCap) database using coded participant identifiers. Direct identifiers will not be entered into the centralized database, and each center will maintain its identification key separately. REDCap will provide role-based access, an audit trail, automated data-validation rules, and standardized data export. Data completeness and consistency will be reviewed periodically, and participating centers will receive queries when clarification or correction is required.

Intraoperative and in-hospital mortality will be recorded. For participants who undergo abdominal aortic aneurysm repair, 30-day vital status will be assessed 30 days after repair. For participants who do not undergo repair, it will be assessed 30 days after the index clinical presentation. Vital status will be verified through institutional medical records or telephone contact when necessary and feasible.

The target enrollment is 2,000 participants. Statistical analyses will be performed using the R statistical software. Receiver operating characteristic curves will be used to evaluate the ability of maximum aneurysm diameter, Aortic Size Index, and Aortic Height Index to distinguish ruptured from intact aneurysms. Areas under the curve and paired differences will be estimated with 95% confidence intervals using a center-level cluster-aware bootstrap. Holm adjustment will be applied to the two primary comparisons, and the paired DeLong method will be used as a sensitivity analysis. Because the indexed measurements are mathematically derived from maximum aneurysm diameter, maximum diameter, Aortic Size Index, and Aortic Height Index will be evaluated in separate mixed-effects logistic regression models. The multicenter structure will be addressed using a random intercept for participating center.