Abstract Body (Do not enter title and authors here): Introduction/Background
Clamping the ascending aorta in acute type A aortic dissection (aTAAD) surgery is an important technique that facilitates proximal procedures such as reinforcement and root replacement during systemic cooling and reduces extracorporeal circulation time. However, in case of aTAAD with thrombosed false lumen, clamping the aorta may lead to serious thromboembolism such as ischemic stroke

Research Questions/Hypothesis
We sought to compare the safety and the efficacy of cross-clamp of the ascending aorta with thrombosed and patent false lumen of aTAAD.

Methods/Approach
From January 2004 to December 2023, a total of 1550 patients with aTAAD underwent emergent surgery at our institution. Among them, 1404 (91%) patients underwent aortic cross-clamp during systemic cooling. The completeness of the cross-cramp was 99.9%. They were divided into 2 groups based on the false lumen status in the ascending aorta: thrombosed (group T, n=399 [28%]) and patent (group P, n=1005 [72%]). After propensity score matching, 389 patients in each group were matched.

Results/Data
After matching, there were no significant differences in age and male gender ratio between the groups. (Table 1A) Preoperative shock state and malperfusion were also similar. The cannulation site did not differ between the groups (Femoral artery: 79% vs. 84% for group T vs. P, P = 0.11; Subclavian artery: 12% vs. 8.0%, P = 0.12). There were no significant differences in the incidence of ischemic stroke (5.4% vs. 6.2% for group T vs. P, P = 0.65), 30-day mortality ( 2.1 vs. 4.1% for group T vs. P, P = 0.10 ), and spinal cord injury (1.3 vs. 1.0% for group T vs, P, P = 1.00), respectively. (Table 1 B）Logistic regression model revealed that thrombosed type dissection was not an independent risk factor for ischemic stroke (odds ratio 1.13, 95% confidence interval 0.66–1.92; P = 0.66).

Conclusions
Cross-clamp of the ascending aorta in aTAAD surgery was very useful in that the proximal procedures could be performed during systemic cooling. Notably, in patients with thrombosed false lumen, the procedure could be performed safely without increasing the risk of cerebral complications.