Abstract Body (Do not enter title and authors here): Introduction - A double atrium septum is a rare congenital anomaly characterized by a double-walled atrial septum with persistent interatrial space. This could be an asymptomatic presentation but also serve as a nidus of thromboembolic complications. We hereby present a case of a 57-year-old female with a cryptogenic stroke found to have a patent foramen ovale and double atrial septum.

Case Description - A 57 year-old-female with a past medical history of hypertension presented with acute complaints of word-finding difficulty, left-sided neck pain and lightheadedness after a head strike while swimming. She was found to have a right-sided cerebellar stroke. A carotid artery ultrasound showed no evidence of atherosclerotic disease. Her lipid profile was normal. A transthoracic echocardiogram showed a patent foramen ovale with a positive bubble study revealing a large right to left shunt with Valsalva. A transesophageal echocardiogram confirmed a patent foramen ovale with an incidental finding of a double atrial septum with extreme redundancy of septal issue. The patient had a surgical closure of the interatrial septum and resection of the accessory interatrial septum tissue. She developed chronic post-sternotomy pain and subsequently had sternal wire removal.

Discussion - A double atrial septum is a rare congenital anomaly seen as two parallel interatrial septa accompanied by a distinct echo-lucent midline space that expands during systole and contracts during diastole. It can happen embryologically by either the abnormal development of the septum secundum, resorption failure of the superior portion of the septum primum, or the persistence of the left venous valve of the sinus venosus. Typically, individuals with double atrial septum are asymptomatic, but they may encounter cardioembolic events due to the potential thrombi formation in the interatrial space. Communication between the septa increases the likelihood of such events. Unlike atrial fibrillation/flutter, there are currently no established criteria for initiating anticoagulation therapy for double atrial septum, primarily due to its rarity. Some options include antiplatelet agents, oral anticoagulation therapy, and percutaneous or surgical PFO closure. Surgical closure provides a permanent closure of the defect, thereby preventing future paradoxical emboli without the potential risks associated with long-term anticoagulation.