Platypnea: Causes and Clinical Approach
Platypnea is dyspnea that occurs in the upright position and improves when lying down, most commonly caused by intracardiac shunts (particularly patent foramen ovale or atrial septal defects), followed by intrapulmonary shunts and ventilation-perfusion mismatch. 1
Primary Mechanisms
The pathophysiology of platypnea-orthodeoxia syndrome (POS) can be classified into three broad categories 1:
1. Intracardiac Shunting (Most Common)
- Patent Foramen Ovale (PFO) is the most frequently reported site of intracardiac shunt causing platypnea 1, 2
- Atrial Septal Defect (ASD) represents another major intracardiac cause 1, 2, 3, 4
- Atrial Septal Aneurysm (ASA) can also lead to POS 1
- Most patients with intracardiac shunts demonstrate a secondary anatomic or functional defect that facilitates the right-to-left shunting in the upright position 1
2. Extracardiac/Intrapulmonary Causes
- Intrapulmonary arteriovenous malformations create direct vascular shunts within the lungs 1, 4
- Hepatopulmonary syndrome causes intrapulmonary vascular dilations 5
- Lung parenchymal diseases can contribute to ventilation-perfusion mismatch 1
3. Ventilation-Perfusion Mismatch
- Various pulmonary conditions can create V/Q mismatch that worsens with upright positioning 4
- This mechanism may coexist with other etiologies 2
Uncommon and Miscellaneous Causes
- Organophosphorus poisoning represents a rare but important cause, particularly in the context of intermediate syndrome development 5
- Multiple concomitant etiologies can coexist in individual patients, making thorough evaluation essential 2
Clinical Recognition
The hallmark features that should trigger suspicion for platypnea include 3, 4:
- Normal arterial oxygen saturations when supine
- Abrupt decline in oxygen saturation when upright
- Dyspnea that appears or worsens in sitting/standing position
- Symptom relief with recumbency
Diagnostic Approach
Transthoracic echocardiography with bubble study is the preferred initial diagnostic examination 2:
- Standard echocardiography may miss the diagnosis if performed only in supine position 3
- Bubble study should be performed with positional changes to provoke the shunt 2, 4
- Careful review of imaging and thorough clinical assessment are necessary since multiple etiologies may coexist 2
Critical Pitfall
A common diagnostic error occurs when initial echocardiography shows normal findings (including normal ejection fraction) but fails to identify positional shunting 3. Heightened clinical suspicion is essential - if platypnea is suspected based on positional oxygen desaturation, repeat echocardiography with bubble study in both supine and upright positions should be performed 4.
Treatment Implications
When POS results from intracardiac shunting without pulmonary hypertension, percutaneous transcatheter closure of the defect can be curative 4. Surgical closure is also effective and results in marked improvement in oxygen saturation to baseline normal 3.