# Acute Hypoxic Respiratory Failure Secondary to an Intermittent Interatrial Shunt

## TL;DR

A rare case of acute hypoxic respiratory failure caused by an intermittent heart defect is successfully diagnosed and treated.

## Contribution

Demonstrates the importance of advanced imaging in diagnosing intermittent interatrial shunts causing unexplained hypoxia.

## Key findings

- A transesophageal echocardiogram revealed a 2.6 cm² secundum ASD with intermittent right-to-left shunting.
- Percutaneous ASD closure led to significant and sustained improvement in oxygenation.
- Episodic hypoxia was linked to maneuvers increasing intrathoracic pressure, such as Valsalva.

## Abstract

Intermittent right-to-left shunting through an atrial septal defect (ASD) is a rare but significant cause of acute hypoxic respiratory failure. This case highlights the diagnostic and management challenges associated with an intermittent interatrial shunt. A 65-year-old man presented with profound hypoxia requiring mechanical ventilation. Despite an extensive initial workup, including a computed tomography angiogram and transthoracic echocardiography with a bubble study, which was negative for an intracardiac shunt, no definitive cause for his hypoxia was identified. Given persistent clinical suspicion and the episodic nature of the isolated hypoxia, a transesophageal echocardiogram was performed, revealing a 2.6 cm² secundum ASD with intermittent right-to-left shunting, predominantly occurring during maneuvers that increased intrathoracic pressure, such as Valsalva. Key differentials, including pulmonary embolism and pneumonia, were systematically excluded. The patient underwent successful percutaneous ASD closure, leading to significant improvement in oxygenation, with follow-up demonstrating sustained normoxia and stable oxygen saturation. This case underscores the importance of considering an intracardiac shunt in patients with unexplained, episodic hypoxia and demonstrates the necessity of advanced imaging modalities for accurate diagnosis.