Platypnoea-orthodeoxia syndrome

Platypnoea-orthodeoxia syndrome refers to the concomitant occurrence of dyspnea and hypoxemia, respectively, which are precipitated by assuming an upright position and alleviated by assuming a recumbent position ⁴.

Clinical presentation

As the name of the syndrome suggests, the hallmark clinical feature is platypnoea - dyspnea when upright that improves in a supine position. Patients may also have clinical features attributable to the underlying etiology of the syndrome, for example, clinical features of a congenital heart defect.

Diagnosis

Confirmed clinically by the dynamic change of arterial oxygenation with a positional change from supine/recumbent to seated/upright, quantified as follows:

• decrease in arterial PaO2 by 4 mmHg or more
• decrease in arterial oxygen saturation by 5% or more

Gold standard diagnosis is achieved by cardiac catheterization.

Pathology

Etiology

Requires the presence of right-to-left shunting, which is most commonly related to a cardiac etiology i.e. an intracardiac shunt. Extracardiac etiologies have also been described.

• intracardiac shunting
  • patent foramen ovale (PFO) ¹
    • most common association
  • atrial septal defect (ASD)
  • atrial septal aneurysm
  • partial anomalous pulmonary venous return
  • iatrogenic
    • Fontan procedure
  • transposition of the great vessels

The right-to-left shunting may be exacerbated by hemodynamic perturbations, such as right heart failure and pulmonary hypertension, or anatomic factors predisposing preferential flow of blood toward (and across) the interatrial septum ².

• extracardiac shunting
  • intrapulmonary shunt
    • pulmonary arteriovenous malformations (AVM)
    • hepatopulmonary syndrome ³
    • acute respiratory distress syndrome
    • pneumonia
  • ventilation-perfusion mismatch
    • chronic obstructive pulmonary disease (COPD)
    • pulmonary embolism 

Radiographic features

Ultrasound

Echocardiography may be utilized with agitated saline as a contrast medium ('bubble study') to demonstrate the presence of right-to-left shunting.