P718 Unexpected finding during follow up for a suspected arrythmogenic right ventricular cardiomyopathy (ARVC)

Interatrial communication is the most common congenital defect found in adulthood, being the most common ostium secundum variety (70-80%). Superior and inferior sinus venosus defects are less usual, found in the 5-10% of cases of interatrial communication and frequently associated with anomalous pulmonary venous return (APVR). These defects are located near the junction of the superior (5%) or inferior (<1%) vena cava with the right atrium, which makes them difficult to diagnose by transthoracic ecocardiography (TTE). Case description: A 44-year-old man who is being followed up in our electrophysiology consulting with suspicion of ARVC (suggestive CMR with no gene found) after an episode of ventricular tachycardia (VT) 11 years ago. Asymptomatic since then under treatment with atenolol, except for an episode of chest pain that required a coronary computed tomography which described an image compatible with a patent foramen ovale and normal coronary arteries. During the follow-up a cardio magnetic resonance (CMR) is performed which showed a severely dilated right ventricle with diskinetic areas, no volume changes since last CMR (5 years ago) and preserved ejection fraction. A small interatrial communication located infero-posteriorly in the septum drawed our attention. Estimated QP/QS was 1.4. After this finding, we reviewed the CT made 4 years ago, where a flow from the left atrium to the right atrium could be seen. We decided to ask for both a transthoracic echocardiography (TTE) and a transesophageal echocardiography (TEE). TTE showed normal left ventricle, a dilated right ventricle with preserved function, no valvulopathies and normal pulmonary pressure. Shunt test with agitated saline was slightly positive after Valsalva maneuver, and QP/QS was again 1.4. TTE showed a small interatrial communication measuring 1.9x0.8cm, next to inferior vena cava`s drainage. Since right ventricle dilation could be due both to the atrial septal defect (ASD) and to the dysplasia, the case was discussed in the heart team, and as the defect was small, QP/QS was 1.4 and pulmonary pressure was normal we adopted a conservative approach. Inferior sinus venosus defects are one of the least common atrial septal defects. They are located in the atrial septum immediately above the orifice of the inferior vena cava and are often associated with partial anomalous connection of the right pulmonary veins. This location makes it difficult to see by means of a common TTE or TEE, and usually as in our case multimodal approach can be very helpful. Usually patients with this kind of atrial septal defect (ASD), signs of significant shunt (right ventricular volume overload, QP/QS≥1.5) and systolic PA pressure less than 50% of systemic pressure (with pulmonary vascular resistance less than one third of the systemic vascular resistance) are suggested for surgery. In this case the possibility of two pathologies overlapping makes it challenging for diagnosis and treatment. Abstract P718 Figure. Multimodal imaging for diagnosis.