Discussion

Unexplained hypoxemia, systemic desaturation refractory to oxygen and physical examination findings such as continuous murmurs localized to the lung fields are classic hallmarks of PAVMs. According to Braunwald, recurrent epistaxis and visceral AVMs point strongly toward Hereditary Hemorrhagic Telangiectasia (HHT), consistent with this patient’s presentation. CT with contrast is recommended as the primary diagnostic test for defining PAVM anatomy while pulmonary angiography serves both diagnostic and therapeutic purposes. The markedly enlarged venous pouch and feeding artery demonstrated in this case typify high-flow congenital PAVMs associated with HHT.

In terms of pathophysiology, PAVMs cause significant right-to-left shunting, reducing effective pulmonary capillary blood flow and leading to refractory hypoxemia, secondary erythrocytosis and compensatory high cardiac output states. Over time, chronic shunting can contribute to right-sided chamber enlargement and pulmonary hypertension, paralleling this patient's findings of RV volume overload, elevated pulmonary pressures, and multichamber dilation. The hepatic venous congestion seen on CT also corresponds with the development of right-sided heart failure, a known downstream consequence of long-standing high-flow PAVMs.

Management wise, transcatheter embolization is the standard of care for PAVMs with a feeding artery size ≥2–3 mm. Embolization reduces right-to-left shunting and prevents complications such as brain abscess, paradoxical embolic stroke, and heart failure. However, for exceptionally large PAVMs, such as in this case, embolization may be technically complex and may lead to a rise in pulmonary artery pressures, as eliminating a major low-resistance pathway increases perfusion to the remaining pulmonary vascular bed. This necessitates careful pre-procedural hemodynamic assessment and close post-procedural monitoring.