Behind the Defect: Transesophageal Echocardiography Reveals a Concealed Interatrial Band

19-year-old female was diagnosed with an ostium secundum atrial septal defect (ASD) after presenting with shortness of breath for the past two years, which had worsened over the last two months. She also reported chest pain and palpitations for the past two months. Echocardiography revealed a 28 mm ostium secundum ASD with a left-to-right shunt, along with dilated right atrial and right ventricular chambers. There was trivial tricuspid regurgitation (TR) with a TR gradient of 20 mmHg and a right ventricular systolic pressure (RVSP) of 23 mmHg. Due to deficient inferior vena cava (IVC) and posterior rims, the patient was scheduled for minimally invasive surgical closure of the ASD. Intraoperative transoesophageal echocardiography (TOE) revealed a band adjacent to the deficient interatrial septum, towards the left atrium (Figure [1](#fig-cap-0001) ) . This band extended from the coronary sinus to the superior vena cava and was subsequently excised partially ( Figure [2a](#fig-cap-0004) , [b](#fig-cap-0004) ;3) . Figure1. TEE Bicaval view showing Ostium secondum ASD(red arrow) and interatrial septal band (yellow arrow). Figure2a Figure2b Figure2b Figure 2a,b. TEE image showing postoperative status of interatrial septal band which was advertently left out. Figure3. Excised specimen portion of interatrial septal band. DISCUSSION Ostium secundum atrial septal defect (ASD) is the most common form of ASD, accounting for up to 70% of cases. It is characterized by a defect in the region of the fossa ovalis, leading to a left-to-right shunt and chronic right heart volume overload when significant in size. Patients with large defects, like in this case (28 mm), often present in adolescence or early adulthood with symptoms such as exertional dyspnea, palpitations, or chest discomfort due to right atrial and ventricular dilation and increased pulmonary blood flow. In this patient, echocardiography revealed a large secundum ASD with right heart dilation and trivial tricuspid regurgitation, confirming hemodynamic significance. RVSP was 23 mmHg, within normal limits, indicating no pulmonary hypertension. However, deficient IVC and posterior rims precluded device closure. Such rim deficiencies are known limitations for percutaneous closure due to the risk of device embolization or residual shunt, favoring surgical repair [1]. Intraoperative transesophageal echocardiography (TEE) revealed a fibrous band extending from the coronary sinus to the superior vena cava adjacent to the interatrial septum—an uncommon finding. Though the embryological origin of such bands is unclear, they may represent remnants of venous valves or congenital fibrous connections [2]. These structures can interfere with intracardiac flow or complicate closure. Excision must be performed cautiously, as they may be near vital conduction tissues. As Yasuda et al. state, “Manipulation or excision of anomalous interatrial septal structures may increase the risk of atrial arrhythmias due to their proximity to conduction pathways, particularly Bachmann’s bundle and the AV node region” [3]. Tamin et al. similarly emphasize avoiding conduction injury during surgery [4]. This case underscores the role of intraoperative TEE in guiding surgical decisions and identifying unexpected anatomical variants.