Small Secundum Atrial Septal Defects Are Associated With Paradoxical Embolism: A Retrospective Study Using Intra-operative Transesophageal Echocardiography.

BACKGROUND: Paradoxical embolism is a clinically important complication of secundum atrial septal defect (ASD), yet anatomical characteristics predisposing to embolic events remain incompletely defined. We investigated clinical and morphological factors associated with paradoxical embolism among adults undergoing transcatheter ASD closure, with particular focus on ASD size. METHODS: We retrospectively analyzed 270 adults who underwent transcatheter closure of secundum ASD between 2013 and 2024. Patients were classified according to history of paradoxical embolism. ASD morphology, including maximum diameter, was assessed by intra-operative transesophageal echocardiography (TEE). Logistic regression evaluated ASD size continuously (per 1-mm increase) and as a categorical threshold (<10 mm vs. ≥10 mm). RESULTS: Paradoxical embolism occurred in 14/270 patients. Patients with paradoxical embolism had a significantly smaller maximum ASD diameter on TEE (12.92 ± 5.79 vs 16.94 ± 5.96 mm, p=0.02). In univariable logistic regression, maximum ASD size (per 1-mm increase) was inversely associated with paradoxical embolism (odds ratio [OR] 0.88, 95% confidence interval [CI] 0.80-0.98; p=0.02). In multivariable analysis adjusted for age, sex and hypertension, ASD size <10 mm remained independently associated with paradoxical embolism (Firth penalized likelihood, Model 1: OR 7.75, 95% CI 2.51-24.50; p<0.001). CONCLUSION: Smaller maximum ASD diameter, particularly <10 mm, was consistently associated with paradoxical embolism, suggesting that even small ASDs may carry clinically meaningful embolic risk in this closure cohort.