Atypical CTPA contrast timing revealing a suspected right-to-left shunt in a patient with advanced COPD and concurrent pulmonary malignancy

Hypoxemia in chronic obstructive pulmonary disease (COPD) typically arises from ventilation-perfusion (V/Q) mismatch. However, refractory hypoxemia should raise concern for alternative mechanisms, such as intracardiac shunting. This report describes a rare presentation where a catastrophic rise in pulmonary vascular resistance—potentially driven by acute hypoxic vasoconstriction, tumor-related microvascular obstruction, or both—likely unmasked a pre-existing interatrial shunt in a patient with advanced lung disease and a concurrent pulmonary mass. A 66-year-old male with advanced COPD presented with acute dyspnea and was initially treated for an exacerbation. Despite initial improvement, he experienced abrupt, severe refractory hypoxemia 28 h post-admission, necessitating endotracheal intubation. Computed tomography pulmonary angiography (CTPA) excluded pulmonary embolism but revealed near-simultaneous contrast enhancement of the right and left atria before the right ventricle, alongside a left lower lobe mass. Bedside echocardiography indicated severe pulmonary hypertension and a suspected reversed interatrial shunt (Eisenmenger-like physiology). He was successfully extubated in the intensive care unit. Following a shared decision-making process where the family explicitly refused advanced mechanical interventions due to his severe comorbidities, the patient transitioned to palliative care. This case highlights the importance of recognizing CTPA contrast timing abnormalities (“aortic pre-opacification”) as a diagnostic clue for intracardiac shunting.