Abstract Body (Do not enter title and authors here):
Background:
Aortic diameter is the most consistently referenced index in guidelines for ascending thoracic aortic aneurysm (aTAA) repair. However, studies have shown that diameter alone may not be an optimal predictor of mortality. Growing evidence suggests aortic length may improve risk prediction, particularly for patients with smaller aortic diameters. However, the clinical relevance of aortic length remains unclear. Furthermore, while prior studies suggest that indexing aortic diameter to body size or height improves mortality risk prediction, there is limited evidence evaluating whether the same holds true for aortic length. To address this gap, this study investigates the association between mortality and raw aortic length as well as length indexed to patient height and body surface area (BSA).

Methods:
449 veterans with ≥4.0cm aTAA and contrast computed tomography imaging underwent patient-specific three-dimensional reconstruction and retrospective medical record review. Aortic length was measured along the centerline between the aortic annulus and innominate artery. All-cause and aortic-related mortality were assessed using Fine-Gray competing risk regression for raw aortic length, aortic length indexed to height (cm), and aortic length indexed to BSA (using DuBois formula), adjusting for age, aortic diameter, and common aTAA risk factors. Optimal binary cutoffs for length/BSA were identified using maximally selected rank statistics and time-dependent receiver operating characteristic analysis.

Results:
Neither raw aortic length nor length indexed to height was associated with all-cause or aortic-related mortality. In contrast, length/BSA was significantly associated with all-cause mortality in univariate (p = 0.0014) and multivariate analysis (p = 0.023). Optimal thresholds for length/BSA were 63 cm/m² overall, 61 cm/m² for five-year mortality, and 67 cm/m² for ten-year mortality. Patients above 63 cm/m² had significantly reduced survival (p < 0.0001).

Conclusion:
Aortic length indexed to BSA was an independent predictor of all-cause mortality in this veteran aTAA cohort. These findings suggest that a BSA-based length index may enhance risk stratification when compared to aortic length alone. However, BSA involves weight, which varies over time and may not directly reflect intrinsic aortic pathology. Further clinical and biomechanical study of indexed aortic length values is needed to clarify their role in disease progression and mortality.