Refractory hypoxemia following mitral valve edge-to-edge repair: why is it so refractory?

Transcatheter Edge-to-Edge Repair (TEER) is an established therapy for high-surgical-risk patients with severe mitral regurgitation (MR). Iatrogenic atrial septal defects (iASD) are a routine consequence of transseptal puncture, and significant right-to-left shunting (RLS) causing refractory hypoxemia is rare. This report presents a man in his 80s with multiple comorbidities who underwent successful surgery. Despite procedural success confirmed by transesophageal echocardiography (TEE), the patient developed refractory hypoxemia during the early recovery phase while still undergoing mechanical ventilation. Normal airway pressures and partial pressure of end tidal carbon dioxide (PETCO₂) ruled out common pulmonary causes. Postoperative transthoracic echocardiography (TTE) revealed a right-to-left shunt via an iASD, which was promptly closed percutaneously, resulting in rapid resolution of hypoxemia. This report highlights that severe hypoxemia following successful TEER should trigger a suspicion of a RLS, especially in patients receiving mechanical ventilation with positive end-expiratory pressure (PEEP) or anemia. Early recognition and consideration of defect closure is essential when hypoxemia is refractory to conventional ventilatory maneuvers.