Abstract Body (Do not enter title and authors here): Background:
Advances in diagnosis and treatment have led to improved congenital heart disease (CHD) outcomes with more adults undergoing operations into adulthood. Cardiac surgery is associated with post-surgical inflammatory conditions including postoperative pericarditis that confer morbidity and are understudied in the adult CHD (ACHD) population.

Goals/Aims:
To evaluate the incidence and risk factors for developing postoperative pericarditis in ACHD surgical operations.

Methods:
This is a retrospective study of all adult patients with CHD who underwent cardiac surgery between 2015 and 2023 at a major New York medical center. Pericarditis diagnosis required 1) documentation of pericardial inflammation as meeting 2/4 criteria for acute pericarditis (chest pain, friction rub, non-localizing ST-elevations or PR depressions, and new/worsening pericardial effusion) and 2) treatment of pericarditis (NSAIDS, colchicine, steroids, IL-1 inhibition). Surgical data and lesion classification was collected.

Results/Data:
Out of 214 ACHD patients undergoing cardiac surgery (median age 36, IQR [26-53] years, 49% male [Table 1]), 47 patients (22%) developed postoperative pericarditis. The majority (>75%) of cases occurred within the first 7 days, with clinical resolution within 2-4 weeks. Four patients developed recurrent episodes of pericarditis, and no patients experienced clinical tamponade or required urgent pericardial drainage. Those who developed pericarditis were younger and more commonly Asian (33%) or African American (33%) compared to Hispanic (23%) or White (12%) (Table 1). Pericarditis occurred most frequently with shunt repairs (27/73, 37%, p<0.001) and aortic valve replacement (10/29, 34%, p=0.016). Those who underwent septal defect (ASD) repairs (24/61, 39%, p<0.001) with autologous pericardium (16/36, 44%, p=0.001) represented the highest risk group.

Conclusions:
Postoperative pericarditis develops in roughly one in five ACHD cardiac surgical cases, most frequently in those who required autologous patch repair, yet only rarely had long-lasting complications. Our study suggests the need to further understand the natural history, treatment, and prevention of pericarditis in those with ACHD requiring surgery.