Atrial Fistulas as Unusual Cause of Paradoxical Embolism: Prevalence and Percutaneous Treatment

BACKGROUND: Atrial fistulas are an utmost rare cause of right-to-left shunt (RLS) and may be potentially associated with increased risk of paradoxical embolism. OBJECTIVE: This study aimed to assess prevalence, anatomical features and transcatheter treatment of atrial fistulas in a large cohort of patients submitted to percutaneous closure of cardiac RLS sites related to paradoxical embolism. METHODS: All patients submitted to percutaneous closure of patent foramen ovale (PFO) in secondary prophylaxis at our Institution from January 2017 to December 2024 were included. Prevalence, anatomical characteristics and percutaneous treatment of atrial fistulas were reported. RESULTS: Atrial fistulas were found in 12 out of the 1052 patients (1.14%) submitted to interventional cardiac catheterization after supposed paradoxical embolism. In four patients, they were found at the first percutaneous intervention, while in eight patients at the time of treatment of residual shunt after a seemingly successful PFO closure. The diagnosis was suspected at microbubble test and confirmed by selective angiography. In nine patients, the fistula coursed along the atrial septum, in two patients from the superior vena cava-right atrium junction to the left atrium/right pulmonary vein, and in one case from the right atrium to the left atrium/right pulmonary vein. All 12 patients underwent successful percutaneous closure with detachable coils (41%) or vascular plugs (59%). CONCLUSION: Atrial fistulas are relatively rare and subtle cause of paradoxical RLS potentially related to systemic embolism. Knowledge of these rare entities is essential for their diagnosis and treatment that can be successfully achieved by transcatheter approach.