(1710) Severe Hypoxic Respiratory Failure due to PFO Intracardiac Shunt in a Lung Transplant Recipient

Introduction: A patent foramen ovale (PFO) is present in an estimated 25% of the population but is generally considered medically inconsequential without elevated right heart pressures. We present a case where changes in blood flow vectors following a lung transplant (LT) resulted in increased shunting through a PFO.

Description: A 63-year-old male with a history of idiopathic pulmonary fibrosis and pulmonary hypertension (pHTN) treated by left LT complicated by recurrent hospitalizations due to hypoxic respiratory failure without clear etiology. A chest x-ray showed mild atelectasis of the left lung and a Pulmonary CT angiogram showed no pulmonary emboli. The patient had multiple transthoracic echocardiograms (TTE) with bubble studies conflicting on the presence of an atrial intracardiac shunt. With no other clear etiology, a PFO was suspected to be the primary cause of his hypoxemia. A transesophageal echocardiogram showed a right-to-left shunt through a PFO without significant pHTN. The patient was taken for cardiac catheterization where his PFO was definitively diagnosed and then closed. Improvement following PFO closure in the absence of significant pulmonary hypertension was remarkable because it suggests a non-pressure-driven mechanism of trans-PFO shunting in this patient.

Discussion: Hypoxemia following LT can involve many mechanisms, including alveolar collapse, alveolar damage, and VQ mismatch. Two other cases of PFO shunting following left LT have been published with a proposed mechanism of rightward mediastinal shifting leading to redirection of blood flow toward the PFO. Single LT recipients ultimately have a lower oxygenating capacity and would be more sensitive to the stress of right to left intracardiac shunt.
The addition of a bubble study in preoperative LT clearance may limit postoperative complications unrelated to primary graft dysfunction. Studies have suggested augmenting echocardiograms with Valsalva maneuver to increase shunting with another study showing that PFO closure during LT surgery does not increase morbidity and mortality. Further studies are needed to explore the threshold of shunting severity necessary for peri-transplant intervention and its effect on post-procedure outcomes.