Triatrial Appearance in a Patient With Atrial Septal Defect: A Case Report.

Atrial septal defect (ASD) is a common congenital heart anomaly, often diagnosed with relative ease. However, the presence of additional structural abnormalities, such as cor triatriatum dexter (CTD) or a prominent eustachian valve, can create a triatrial appearance, complicating diagnosis and management. Accurate differentiation of these anomalies is essential to guide appropriate clinical decisions. We report the case of a 25-year-old male with exertional dyspnea and fatigue. Cardiovascular examination revealed a wide, fixed splitting of S2 and a systolic murmur. Transthoracic echocardiography (TTE) suggested an ostium secundum ASD (OS-ASD) with an abnormal membrane in the right atrium, raising suspicion for CTD. Further evaluation with transesophageal echocardiography (TEE) and cardiac computed tomography (CT) revealed an incomplete CTD (iCTD) rather than a true triatrial division. Cardiac catheterization confirmed an operable left-to-right shunt with mild pulmonary arterial hypertension. The patient underwent successful ASD closure and membrane excision. This case highlights the importance of multimodality imaging in distinguishing a triatrial appearance in ASD patients. Misdiagnosis of iCTD as CTD or a prominent eustachian valve can lead to inappropriate management decisions. Advanced imaging techniques, including three-dimensional TEE (3D TEE) and cardiac CT, are crucial for precise anatomical assessment and surgical planning, ensuring optimal patient outcomes.