Platypnea–orthodeoxia syndrome: a rare presentation of infer
The present case has been reported in the European Heart Journal Case Reports.

A 69-year-old patient with a history of high blood pressure and a left nephrectomy due to a myxoid liposarcoma 2 years before. He reported shortness of breath on moderate exertion that began 15 days before.

Physical examination revealed hypotension (95/55 mmHg), 125 b.p.m. and an oxygen saturation (SatO2) of 85%, associating tachypnoea and intercostal retractions. After adopting decubitus, there was an improvement of ventilatory mechanics with SatO2 of 94%, normalization of blood pressure levels, and heart rate, all resulting in the platypnea–orthodeoxia syndrome (POS).

The cardiac and pulmonary auscultations were normal, without lower limb pain or oedema. The electrocardiogram showed a sinus tachycardia with S1Q3T3 pattern. Chest radiograph showed no pathological findings. Blood tests revealed a D-dimer of 4000 ng/mL, normal renal function and an alveolar-arterial oxygen gradient of 69 mmHg (NV: <30) with no other remarkable findings. A CT angiography of the pulmonary arteries ruled out pulmonary thromboembolism.

At admission, prophylactic anticoagulation was started to prevent pulmonary thromboembolism. The echocardiography revealed a normal morphology and function of both ventricles and atriums, without valvulopathies, septal defects, or visible thrombus. The bubble study was normal (Supplementary material online, Video S3). The spirometry, revealed no disorders. Therefore, an extracardiac shunt was the most likely mechanism.

On the third day of hospitalization, the patient presented abrupt haemodynamic deterioration with signs of peripheral and central hypoperfusion. An urgent thoracoabdominal CT revealed a large occlusive thrombus in the inferior vena cava from the right atrium to the right renal vein, putting in context a renal tumour recurrence.

The presence of the thrombus determined the decrease of the venous return and the right heart preload specially during orthostatism, clinically observing hypotension and low SatO2, partially corrected during decubitus.

Although intensive treatment was promptly started, the patient presented rapidly progressive clinical deterioration, deceasing a few hours later.

Lessons learnt:-
- Platypnea–orthodeoxia syndrome is recognized by dyspnoea while standing or seated and normal breathing lying.

-It might be caused by right-left shunt or ventilation/perfusion mismatch.