Tricuspid-regurgitation-mediated flow-driven right-to-left cardiac shunting caused systemic hypoxemia in a patient with patent foramen ovale without elevated right atrial pressure

The prevalence of patent foramen ovale (PFO) is 20–25% among adults. The role of right-to-left shunting through the PFO in systemic hypoxemia remains poorly understood. Right-to-left shunting through the PFO can occur either due to elevated right atrial pressure (pressure-driven) or directed venous flow toward the PFO (flow-driven). Herein, we report a rare case of flow-driven right-to-left shunting via the PFO in a patient with traumatic tricuspid regurgitation. A 45-year-old Chinese woman was admitted due to progressive dyspnea for 3 years, presenting with cyanosis and digital clubbing. She was hypoxic, with an oxygen saturation of 83% on room air, and arterial blood gas showed an oxygen tension of 53 mmHg. Echocardiography showed severe tricuspid regurgitation with ruptured chordae tendinea, causing regurgitant jet flow directed toward the interatrial septum, leading to intermittent right-to-left shunting between the septa primum and secundum. Swan–Ganz catheterization revealed normal-high right atrial pressure and excluded pulmonary hypertension. The patient underwent tricuspid valve repair and PFO closure. Her oxygen saturation returned to 95% and her symptoms resolved. Right-to-left shunting through the PFO could cause systemic hypoxemia via a flow-driven mechanism, occasionally manifesting as cyanosis and clubbing digits. PFO closure and treatment of underlying disease are effective in improving hypoxemia.