Persistent Hypoxemia in a Young Patient: Beyond Pulmonary Embolism

Pulmonary embolism is one of the leading causes of acute dyspnea and hypoxemia, yet its diagnosis becomes challenging when clinical findings and imaging studies are discordant. We report the case of a 35-year-old woman whose only relevant history was systemic hypertension, who presented with three months of progressive dyspnea, orthopnea and palpitations, a pO2 of 56 mmHg, an oxygen saturation of 85% and polycythemia. Pulmonary computed tomography angiography showed no filling defects, whereas lung scintigraphy reported a high probability of pulmonary embolism. Transesophageal echocardiography identified an ostium secundum atrial septal defect with bidirectional shunting and severe tricuspid regurgitation, and right heart catheterization confirmed moderate precapillary pulmonary hypertension, a left-to-right shunt and a filling defect in the right pulmonary artery. The coexistence of an intracardiac shunt and pulmonary vascular disease creates a hybrid pathophysiological scenario that distorts both the clinical and the imaging presentation; in the setting of unexplained persistent hypoxemia, the diagnostic work-up must extend beyond pulmonary embolism.