["On and off" hypoxaemia]

Area of Science:

• Cardiology
• Diagnostic Imaging

Background:

• Platypnoea-orthodeoxia syndrome necessitates consideration of right-to-left shunts, often attributed to patent foramen ovale (PFO).
• Saline contrast transthoracic or transoesophageal echocardiography is the primary diagnostic tool for PFO.

Observation:

• An eighty-year-old woman presented with platypnoea-orthodeoxia syndrome but initially showed no signs of a right-to-left shunt via PFO.
• Standard supine lung scintigraphy and echocardiography were normal, despite strong clinical suspicion of PFO.

Findings:

• Repeating imaging in the upright position revealed a right-to-left shunt.
• This shunt was caused by an aneurysm of the ascending aorta displacing the interatrial septum, allowing blood flow from the inferior vena cava through a PFO into the left atrium.

Implications:

• Diagnosis of PFO can be difficult, underscoring the importance of repeat saline contrast echocardiography in the upright position if supine tests are negative.
• Contrast infusion via femoral veins can confirm PFO diagnosis when standard methods are inconclusive.