What is platypnoe and how is it managed?

Platypnea: Definition and Clinical Significance

Platypnea is positional dyspnea that worsens in the upright position and improves when lying supine, often accompanied by orthodeoxia (positional arterial oxygen desaturation). 1, 2

Pathophysiology

Platypnea-orthodeoxia syndrome (POS) requires two essential components to manifest clinically:

• An anatomical vascular defect that allows right-to-left shunting, most commonly a patent foramen ovale (PFO), but can also include pulmonary arteriovenous malformations (PAVMs) or other intracardiac/intrapulmonary communications 1, 3, 4

• A functional component that promotes positional shunting, which can occur even without elevated right atrial pressures or right heart failure 4, 5

The mechanism involves preferential streaming of venous blood across the defect when upright, bypassing normal pulmonary capillary filtration and gas exchange. 6, 2 In PAVMs specifically, 65% to 83% are located in the lower lobes, making positional symptoms particularly prominent. 6

Clinical Presentation

The hallmark features include:

• Dyspnea that dramatically worsens when sitting or standing and resolves within minutes of lying flat 2, 5
• Oxygen desaturation in the upright position, which can drop from 96% supine to 86% or lower when upright 2
• Cyanosis that appears only in the upright position and disappears when supine 2
• Potential for paradoxical emboli causing transient ischemic attacks or strokes (3.2%-55% in PAVM patients) 6, 3

Diagnostic Approach

The diagnosis is established through position-dependent testing that demonstrates the pathognomonic pattern:

• Pulse oximetry in both supine and upright positions to document orthodeoxia, showing significant oxygen saturation drops (typically >5%) when upright 2, 5

• Transthoracic echocardiography with agitated saline (bubble study) performed in both positions, as shunting may only be apparent when upright 5

• Transesophageal echocardiography to definitively identify and characterize intracardiac shunts like PFO 4, 5

• CT angiography to detect PAVMs, particularly in lower lobes where they are most common 6

• Right heart catheterization with oximetry runs in both supine and upright positions to quantify shunt fraction and document positional changes in hemodynamics 2, 4

Critical Diagnostic Pitfall

Standard supine-only evaluation will miss this diagnosis entirely, as shunting and desaturation may be completely absent when the patient is lying flat. 5 Always evaluate suspected cases in the upright position.

Management Strategy

For Intracardiac Shunts (PFO)

Percutaneous closure of the PFO is first-line definitive therapy and can completely cure symptoms. 4, 5

• Catheter-based occlusion devices (such as Amplatzer occluders) provide safe and effective closure 4
• Post-closure, oxygen saturation typically normalizes and remains stable in all positions 2, 4
• This approach is curative even in patients with normal cardiac hemodynamics and no right heart failure 4

For Pulmonary Arteriovenous Malformations

Percutaneous transcatheter embolization of the feeding artery is the treatment of choice. 6

• Any PAVM detected should be considered for treatment regardless of feeding artery size, due to paradoxical embolism risk 6
• Embolization uses coils or plugs deployed as close to the arteriovenous communication as possible 6
• Follow-up CT angiography at 6-12 months, then every 3-5 years, is recommended to detect persistent or new lesions 6
• Persistence rates vary by embolic material: 5-21% for coils alone, 4-6% for nitinol plugs, 0-2% for microvascular plugs 6

Symptomatic Management Pending Definitive Treatment

While arranging definitive intervention, provide supportive care:

• Maintain the patient in supine or semi-recumbent position to minimize shunting 2, 5
• Supplemental oxygen to maintain adequate saturation, though higher flow rates may be needed in the upright position 2
• Cool air directed at the face and optimal positioning can provide comfort 7

Special Considerations

In patients with hereditary hemorrhagic telangiectasia (HHT), who account for 70-90% of PAVM cases, screen for additional vascular malformations and counsel about pregnancy risks, as PAVMs can grow rapidly due to hormonal and hemodynamic changes. 6