668: Acute Pulmonary Embolism Complicated by Bidirectional Atrial Septal Defect

Introduction: Atrial septal defects (ASD) are a common congenital defect. They can be surgically repaired in childhood but can also be unnoticed until the fourth or fifth decade of life. ASDs are often asymptomatic until the intracardiac left to right shunting and excess right heart strain causes remodeling of the heart muscle and pulmonary hypertension. Description: 60s-year-old female with history of hypertension and heart murmur presented as a transfer to our medical center for management of high-risk pulmonary embolism with right heart failure and pulmonary hypertension evident on echocardiogram. Further investigation discovered a previously undiagnosed 3 cm atrial septal defect, with left to right blood flow. Patient improved with nebulized epoprostenol and diuresis until there was evidence of right to left shunting through the ASD, believed to be secondary to systemic hypotension. As such, patient became hypoxic refractory to maximal ventilatory support, subsequently was started on intravenous treprostinil, and was placed on Veno-arterial Extra Corporeal Membrane Oxygenation (VA-ECMO). While on ECMO, patient had bidirectional shunting through the ASD which created a challenge to manage patient’s oxygenation and weaning from ECMO circuit. Ultimately, patient was decannulated after an extended hospital course and recovered without any focal neurologic deficit. Discussion: Patients with large ASDs discovered later in life may become dependent on bidirectional shunting for hemodynamic stability. This patient’s acute decompensation was likely due to a decrease in systemic vascular resistance (SVR), which, in the context of pulmonary hypertension, led to right-to-left shunting and refractory hypoxemia. In patients with ASDs, shunt reversal—from left-to-right to right-to-left—can occur due to a sudden increase in pulmonary vascular resistance (PVR) or a decrease in SVR. Optimizing pulmonary hypertension management may not consistently improve arterial oxygen saturation, and decisions regarding ECMO weaning should be based on the overall clinical picture rather than laboratory values alone. These patients live with chronic hypoxemia and may demonstrate a higher tolerance to low oxygen levels.