Abstract Body (Do not enter title and authors here): Introduction:
Aspirin has been associated with slower progression and rupture prevention of abdominal aortic aneurysms. However, its effect on ascending thoracic aortic aneurysms (ATAAs) remains unclear. We investigated whether aspirin use slows aneurysm growth in veterans with ascending aortic dilation or ATAAs under surveillance.

Research Question/Hypothesis:
We hypothesized that aspirin use would be associated with slower aneurysm growth.

Methods:
We conducted a retrospective cohort study of 1,004 patients with ascending aortic dilation (diameter ≥ 40mm) at a Veterans Affairs Healthcare system. Patients with ≥2 computed tomography (CT) scans and ≥3 months between scans were included. Exclusion criteria included prior repair, dissection, or single imaging. Clinical data, aspirin use and dose, imaging intervals, and aneurysm outcomes were reviewed. Growth rate was calculated from serial CT imaging. Patients with and without aspirin use were compared using Welch’s t-test. Linear regression models were used to evaluate aspirin's independent association with growth rate.

Results:
Of 628 patients meeting criteria, 231 (36.8%) were taking aspirin. Mean age was 75.6 ± 8.3 years, and 100% were male. Comorbidities included smoking history (n=437, 69.5%), hypertension (n=520, 82.7%), and hyperlipidemia (n=463, 73.6%). Mean imaging follow-up was 4.58 years, and aspirin doses ranged from 81 to 325 mg. Patients taking aspirin had a significantly slower mean aneurysm growth rate (−0.19 mm/year) compared to non-users (0.16 mm/year, p=0.025). In univariable linear regression, aspirin use was associated with decreased aneurysm growth rate (β = −0.35 mm/year, p=0.024). This association persisted in a multivariable linear regression model adjusting for baseline aortic diameter (β = −0.36 mm/year, p=0.024). Baseline diameter was not significantly associated with growth rate (p=0.18).

Conclusion:
In this male veteran cohort, aspirin use was independently associated with significantly slower ATAA growth. This association remained robust in both univariable and multivariable models, suggesting aspirin may exert protective effects independent of aneurysm size. Given its anti-inflammatory properties, aspirin warrants further investigation in prospective trials as a potential medical therapy for ascending thoracic aortic aneurysm management.