b'Scientific Session Abstracts SATURDAY APRIL 20, 2024 18: THE IMPACT OF TIMING OF THORACIC ENDOVASCULAR AORTIC REPAIR ON THE POSTOPERATIVE OUTCOMES OF PATIENTS WITH UNCOMPLICATED TYPE B AORTIC DISSECTIONNarek Veranyan, MD 1 ; Mohammed Hamouda, MD 1 ; Nadin Elsayed, MD1;Omar Al-Nouri, DO, MS, RPVI, FACS 1 ; Phillip Goodney, MD, MS 2 ;Mahmoud B. Malas, MD, MHS, RPVI, FACS 11Department of Surgery, Division of Vascular & Endovascular Surgery,UC San Diego, San Diego, CA,2 Section of Vascular Surgery, Dartmouth-Hitchcock Medical Center, Lebanon, NHBackground: Thoracic endovascular aortic repair (TEVAR) is used to induce a favorable aortic remodeling in select patients with uncomplicated type B aortic dissection (uTBAD) although the impact of timing of TEVAR on the postoperative outcomes is not completely understood. The purpose of this study is to investigate the impact of TEVAR timing on the 30-day postoperative clinical outcomes of patients with uTBAD using a multi-institutional database.Methods: The Vascular Quality Initiative (VQI) database was studied for all patients who underwent TEVAR for uTBAD excluding cases of aortic rupture or malperfusion. The study cohort was divided into TEVAR timing groups: 14 days (acute), 14-30 days (subacute), and 30 days (chronic) since the onset of dissection. Demographic, clinical, perioperative characteristics, and postoperative complications including overall mortality, disease/treatment-related mortality, and Major Adverse Cardiovascular Events (death, myocardial infarction, stroke) were compared between groups. Univariable and multivariable regression analysis was conducted, and model performance was evaluated with discrimination analysis using the Receiver OperatingCharacteristic curve and Area Under the Curve (AUC).Results: Out of 29,115 patients, 1,854 met the inclusion criteria, of which 1,304 (70.3%) underwent TEVAR in the acute, 188 (10.1%) in the subacute, and 362 (19.5%) in the chronic setting. Table 1 demonstrates the association of TEVAR timing with baseline characteristics. For all indications of TEVAR, except for aneurysmal degeneration, the odds of overall mortality (OR: 0.10, p=0.016), disease/treatment-related mortality (OR: 0.12, p=0.048) and MACE (OR: 0.08, p=0.007) significantly decrease for patients undergoing TEVAR in the chronic vs acute setting. Odds of overall mortality (OR: 0.16, p=0.050) and MACE (OR: 0.13, p=0.027) were also significantly lower in the chronic compared to the subacute setting (Table 2). Postoperative mortality of uTBAD patients undergoing TEVAR for aneurysmal degeneration does not change with TEVAR timing (OR: 0.43 95%CI [0.09-1.97], p=0.278). The AUC of the ROC curve for mortality is 82.21% (Figure 1).Conclusions: The risks of postoperative mortality and MACE of patients undergoing TEVAR for uTBAD decrease when TEVAR is performed beyond 30 days from the onset of symptoms, except for patients with aneurysmal 42 NDANNUAL MEETING|APRIL 1921, 2024|OCEANSIDE, CA 51'