Abstract Body (Do not enter title and authors here): Introduction.
Thoracic endovascular aortic repair (TEVAR) has emerged as a promising treatment option for patients with type B aortic dissection (TBAD). However, there is a lack of evidence regarding the long-term morbidity of initial TEVAR compared to optimal medical therapy (OMT) in acute uncomplicated TBAD (uTBAD).

Objective.
To evaluate real-world data(RWD) on the long-term outcome of Japanese patients with acute uTBAD using a nationwide claims database.

Methods.
This retrospective cohort study utilizes JMDC, a nationwide claims database under Japan's universal healthcare system. We included patients who were initially hospitalized with a diagnosis of acute TBAD. We defined acute uTBAD by excluding those who died within one month, suffered aortic rupture, traumatic thoracic aortic injury, underwent open-chest surgery, experienced stroke or paralysis, or had less than six months of history in the JMDC. Patients who underwent TEVAR within three months of the index hospitalization (TEVAR group) were compared with those who received optimal medical therapy (OMT group). Propensity score (PS) matching was performed based on age, sex, and year of hospitalization. Using the Kaplan-Meier method, we calculated the cumulative rate of all-cause mortality and aorta-related events.

Results.
Of 18,445 patients diagnosed with aortic disease between January 2005 and December 2020, 641 were included in the study (OMT group: n=580, TEVAR group: n=61). After PS-matching, demographics of the groups (OMT_PSM: n=183 vs. TEVAR_PSM: n=61) were female (12.6% vs. 13.1%), median age (54 years [IQR, 48-60] vs. 54 years [IQR, 50-61]) and follow-up time (18 months [8-32] vs. 19 months [9-32]), respectively. Kaplan-Meier curves for the aortic-related events (Figure1, 2) are shown as long-term outcomes.

Conclusions.
This study successfully demonstrated that the estimated 5-year aortic-related event rate in acute uTBAD patients undergoing OMT is approximately 20%, demonstrating the relevance of the RWD source. However, the number of death events in the TEVAR and OMT groups was not sufficient to provide statistical power. Therefore, further studies are warranted to evaluate the long-term prognosis of initial TEVAR for uTBAD.