Platypnea Orthodeoxia Syndrome - Causes, Diagnosis, and Treatment

Introduction:

Platypnea orthodeoxia syndrome (POS) is a rare pulmonary syndrome in which platypnea and orthodeoxia are seen. Platy - means flat, and apnea - means breath. Platypnea is shortness of breath when sitting up and is relieved by lying down, opposite to orthopnea. Ortho - means erect, and deoxia - means no oxygenation. Therefore it is characterized by dyspnea and deoxygenation on sitting in an upright position and relieved by lying down.

What Are the Causes of Platypnea Orthodeoxia Syndrome?

Platypnea orthodeoxia syndrome can be caused by the following conditions:

• Intracardiac shunting.

• Intrapulmonary shunting.

• Ventilation-perfusion (V/Q) mismatch.

• Combination of all three.

The most common defects are-

• Pulmonary Defects:

  1. Multiple pulmonary emboli.

  2. Pulmonary emphysema.

  3. Pulmonary arteriovenous malformations (PAVM).

  4. Fat embolism syndrome.

  5. Hepatopulmonary syndrome.

  6. Radiation-induced bronchial stenosis.

• Cardiac Defects:

  1. Patent foramen ovale (PFO) - most common.

  2. Pericardial effusion.

  3. Atrial septal defect (ASD).

  4. Constrictive pericarditis.

  5. Aortic aneurysm.

  6. Tricuspid regurgitation.

  7. Mediastinal shift.

• Miscellaneous Disorders:

  1. Parkinson's disease.

  2. Bilateral thoracic sympathectomy.

  3. Hepatic cirrhosis.

  4. Ileus.

What Are the Diagnostic Tests to Be Carried Out?

The clinical presentation of POS can be very little and requires meticulous history taking to reach a diagnosis.

• Oxygen saturation levels must be analyzed in supine and upright positions. If a drop in oxygen saturation of more than five percent is observed in the upright position, with recumbency improvement, a POS diagnosis can be made.

In the presence of a large right-to-left, treatment with 100 percent oxygen may not be able to show significant improvement.

• The next step is to identify the underlying mechanism of desaturation. Since cardiac-related etiology is the most commonly seen, echocardiography with bubble-related contrast with intravenous agitated saline is the first diagnostic test. The test can be performed in both supines as well and upright positions. The test can help differentiate patients with an intracardiac shunt from an extracardiac shunt. The appearance of bubbles in the left atrium within three cardiac cycles

suggests an intracardiac shunt. A delayed microbubble opacification of the left atrium (after three to six cardiac cycles) suggests an extracardiac shunt, most commonly in the pulmonary vasculature.

• A transesophageal echocardiography (TEE) can be performed to visualize the cardiac defect or aneurysms if a transthoracic echocardiogram is inconclusive.

• In case of high suspicion with an indeterminate echocardiographic study, cardiac magnetic resonance imaging (MRI) may be used to look for distortion of the cardiac anatomy leading to right-to-left shunting.

• In case of the absence of intracardiac findings, other causes of POS due to intrapulmonary shunting should be investigated. A ventilation-perfusion (V/Q) scan can be performed to assess for extra-pulmonary uptake.

• A perfusion scan scintigraphy (technetium-99 melabeled macro-aggregated albumin injected in the peripheral vein for lung scanning) can be used to assess changes in pulmonary perfusion with positional change (upright versus lying down). This test can also estimate the shunt fraction using the quantitative uptake in the brain or kidney.

• If an extracardiac shunt is suggested from an echocardiogram, a computerized tomographic (CT) angiography of the chest can be performed to assess for pulmonary arteriovenous malformations.

• Pulmonary arteriography is considered the standard gold test to diagnose causes of intrapulmonary shunts where uncertainty persists after other tests have been exhausted.

What Is the Treatment of Platypnea Orthodeoxia Syndrome?

The management of the underlying etiology is the key to the resolution of POS. The definitive treatment of POS due to an intracardiac shunt involves correcting the primary cardiac anomaly. This may involve closure of the patent foramen ovale (PFO) or surgical repair of the ASD. A definitive decision regarding treatment is undertaken after careful assessment of the patient and due consideration of the risk-to-benefit ratio of the procedure. While for several years, surgery has been the mainstay for the closure of PFO and ASD, the percutaneous intervention has supplanted it recently due to decreased mortality and lower cost.

The American college of cardiology/American heart association (ACC/ AHA) guidelines recommend ASD closure in patients with right atrial and right ventricular enlargement. Smaller ASDs of diameter less than 5 mm with no evidence of right ventricular enlargement or pulmonary hypertension do not require closure unless associated with POS or paradoxical embolism. Percutaneous closure can be performed using a buttoned device, cardioseal septal occlusion system, and amplatzer septal occluder. Symptomatic improvement with percutaneous closure is observed in more than 95 % of patients.

The most common extracardiac cause of POS is PAVM. Pulmonary artery embolization is commonly performed in patients with a symptomatic primary pulmonary arteriovenous malformation with a feeding artery of more than 2-3 mm. The usual embolic materials are metallic coils (steel, titanium, or platinum) or detachable balloons. Alternative embolic materials include polyvinyl alcohol, wool coils, and amplatzer vascular plugs. Potential benefits of the amplatzer plugs over conventional coils include more rapid occlusion of PAVM, a reduced procedure time, the ability to occlude more PAVM in a single session, occlusion of feeding vessels with shorter necks, theoretical reduction of paradoxical thrombus embolization during the procedure, and a potentially lower incidence of later reperfusion.

Lung surgery is rarely the treatment of choice and is performed in patients with life-threatening rupture of the arteriovenous malformations or patients not amenable to embolotherapy. Lung transplant is an option in patients refractory to treatment and with diffuse bilateral pulmonary AVMs.

For patients with primary parenchymal lung disease, treatment of the underlying

pulmonary condition leads to improved V/Q matching with subsequent resolution of POS.

Liver transplantation is the only definitive therapy for patients with hepatopulmonary syndrome leading to POS. After transplantation, most patients show improvement in oxygenation. No other medical treatment has shown effective results. Standard therapy with spironolactone can paradoxically worsen the condition. Coil embolotherapy is highly unsuccessful in a patient with HPS with a large pulmonary arteriovenous shunt and only showed temporary improvement in arterial saturation. Thus, these patients with severe HPS should receive high priority in liver transplantation.

Conclusions:

It is essential to have a high index of suspicion to detect POS in patients with dyspnea, given the subtle and positional nature of the symptoms. Physicians should consider POS in patients with unexplained dyspnea. POS can be through cardiac or non-cardiac-related mechanisms. As described above, a systematic evaluation is necessary to identify the underlying cause. Appropriate interventions are directed toward correcting the cause of POS. Management of underlying causes is the key to the resolution of POS. The treatment modalities could alleviate symptoms and be potentially curative.