Abstract Body (Do not enter title and authors here): Atrial fibrillation occurs in a growing number of adults with congenital heart disease (ACHD); however, recommendations for procedural considerations are lacking.

A 43-year-old woman with surgical repair of sinus venosus ASD and partial anomalous pulmonary venous return and history of atrial arrhythmias and sinus node disease presents for repeat ablation procedure for persistent atrial fibrillation. Echocardiogram two days prior to ablation procedure demonstrated no SVC stenosis, known left SVC with dilated coronary sinus (CS), and moderate LV systolic dysfunction, presumed due to persistent atrial fibrillation with tachycardia. The AF ablation was performed with intracardiac echo guidance of trans-septal puncture. All four pulmonary veins were confirmed to be isolated from prior ablation. Right and left atria were mapped during atrial fibrillation using Volta Medical to identify dispersion areas, which identified areas of spatial dispersion in the posterior wall and coronary sinus, for which posterior wall isolation was performed with CS ablation set. AF was converted to AFL with ablation and patient was cardioverted to junctional rhythm, her known baseline rhythm. At conclusion of the study no pericardial effusion was noted by ICE. Post-procedure, the patient continued to have junctional rhythm and hypotension requiring vasoactive support; limited bedside echo demonstrated no effusion. Due to persistent hypotension, additional echo imaging was performed which demonstrated no pericardial effusion, normal LV systolic function; however, an echo lucency posterior to aorta with compression of left atria was seen. CT scan confirmed a hematoma surrounding LA, 7.2 x 3.3 cm, with compression on left superior vena cava. No surgical intervention was performed due to contained hematoma and clinical stability, as surgical evacuation of the hematoma would increase the risk of bleeding. Repeat CT at 7 days demonstrated stable mediastinal hematoma of 7.2 x 3.3 cm. The patient continues to be monitored clinically with serial imaging.

In ACHD patients, ablation complicated by perforation may be underrecognized due to prior surgical scarring, which may contain bleeding and obscure findings on limited imaging due to lack of circumferential effusion. Heightened vigilance and tailored procedural and post-procedural imaging strategies are necessary for ablation procedure in ACHD patients, considering their unique anatomy and surgical history