Ventilation / perfusion mismatch in patient with chronic dyspnea after COVID-19 recovery.

A 56-year-old female presented with persisting dyspnea. Four months before she was hospitalized with PCR confirmed SARS-CoV2 pulmonary infection, requiring tracheal intubation in ICU because of ARDS. In the moment of the consultation she was SARS-CoV2 RT-PCR -, and blood test showed IgM –, IgG+ antibodies. Oxygen saturation was 92%.

Dual-energy chest CT after intravenous contrast administration was performed in order to depict complications such as pulmonary fibrosis, pulmonary thromboembolic disease or perfusion disturbances.

CT revealed persistence of diffuse multifocal, bilateral and peripheral ground-glass opacities predominantly in upper lobes and right middle lobe, and areas of crazy paving. Dilated subsegmental vessels were seen proximal and within the opacities. Subpleural bands and architectural distortion areas were present in both lower lobes (Fig 1 a-c) Filling defects were not present in pulmonary arteries or branches, showing no signs of pulmonary embolism. No pleural fluid or enlarged lymph nodes were present.  

Pulmonary blood volume showed wedge-shaped areas of decreased perfusion predominantly in posterior segments of both lower lobes, not demonstrating correlation with the areas of ground glass opacities or crazy paving. There weren’t areas of complete absence of perfusion suggesting pulmonary infarction (Fig 2a, 2b, 3a and 3b).

Background

SARS-CoV-2 has high affinity for angiotensin-converting-enzyme 2 (ACE 2)Virus complex enters via endocytosis, ACE2 surface is downregulated,leadin+g to increased circulating angiotensin II (AT-II) and AT-II receptor activation [1, 2]. Angiotensin  stimulates vasodilatation and nitric oxide production. AT-II promotes vasoconstriction and fibrosis [3].Pyroptosis secondary to virus infection of alveoli cells, promotes an intense pro-inflammatory cascade [1], damaging alveolar-capillary barrier [1,2],leading to a generalized vascular disturbance.

Clinical perspective

Imaging Perspective

Some studies show different abnormal lung perfusion patterns in COVID infection. Four of them were described by Lang M [6 - 8]: areas of heterogeneity on the pulmonary blood volume images with alternating higher and lower perfusion (mosaic perfusion); areas of relative increase in perfusion compared to background lung (focal hyperemia pattern); areas of relative decrease in perfusion compared to background lung (focal oligemia pattern); rim of increased perfusion around an area of lung perfusion compared to background lung, corresponding to parenchymal opacity (“hyperemic halo” sing) Those imaging manifestations are explained by an increased blockage of ACE2 receptors  in the lung endothelium, increased local levels of angiotensin II, and subsequent vasoconstriction and ventilation / perfusion mismatch [1].

Complete pulmonary emboli usually manifests as wedge-shaped perfusion defects at the subpleural portion of the corresponding lung parenchyma. Incomplete occlusion may not show perfusion defects. [9]

Motion artifacts can be seen as bandlike or crescent-shaped defects in color-coded perfusion maps [9]. In our case, perfusion defects were more extensive than explained by those artifacts.

Outcome

After discharge, patients with severe acute respiratory syndrome (SARS) can suffer symptoms as exertional dyspnea for long time due to residual pathological changes or muscle weakness [10, 11]. In patients with COVID-19, pathological changes are not dominant, suggesting a different underlying cause.

Clinical trials suggest that pulmonary rehabilitation combined with patient exercises is effective for improving dyspnea after COVID-19 infection [11]. Recently, guidelines have been created to advise people with “long covid” in daily routine (www.longcovid.org) [12]. Multidisciplinary approach and follow-up are essential to individualized care plans and to evidence long-term outcomes.

Take-Home Message / Teaching Points

Dual-energy CT imaging shows vascular lung disturbances in patients with passed COVID infection and persisting symptoms.

Further studies are needed to understand the prognostic implication of such radiological features.