DVTs and PEs: Imaging’s Role in Managing Blood Clot Dangers in COVID-19

COVID-19 has been described primarily as a pulmonary disease, but growing evidence and analysis of imaging and outcomes points to a vascular involvement, particularly complications that are associated with blood clots that develop in patients infected with the virus.

As a growing number of recent reports reveal a strong association between elevated D-dimer levels - an indicator that points to the likely presence of a blood clot - and poor prognosis in this patient group, the National Institute for Public Health of the Netherlands asked a group of radiologists and vascular medicine specialists to draft guidance for imaging and treating these complications.

Their recommendations for prevention, diagnosis, and treatment were published on April 23 in Radiology.

“Worldwide, COVID-19 is being treated as a primary pulmonary disease,” said Edwin J.R. van Beek, M.D., Ph.D., director at Edinburgh Imaging, Queens Medical Research Institute, at the University of Edinburgh, U.K. “From the analysis of all available current medical, laboratory, and imaging data on COVID-19, it became clear that symptoms and diagnostic tests could not be explained by impaired pulmonary ventilation alone.”

As more is learned about how the virus affects the body, clinicians are learning that respiratory failure in patients is driven by more than the development of acute respiratory distress syndrome. Microvascular thromobotic processes are also having an impact. In fact, existing studies not only point to the strong association between D-dimer levels, disease progression, and chest CT that suggests venous thrombosis, but they also highlight the link between increased D-dimer levels and severe disease and poor prognosis among COVID-19-positive patients.

Consequently, the report authors said, providers must pay close attention to the initial diagnosis and treatment of the prothrombotic and thrombotic state that has been seen to occur in a significant portion of COVID-19 patients.

“Imaging and pathological investigations confirmed the COVID-19 syndrome is a thrombo-inflammatory process that initially affects lung perfusion, but consecutively affects all organs of the body,” van Beek said. “This highly thrombotic syndrome leads to macro-thrombosis and embolism. Therefore, strict thrombosis prophylaxis, close laboratory and appropriate imaging monitoring with early anti-coagulant therapy in case of suspected venous thromboembolism are indicated.”

The study authors made several recommendations for diagnostic and therapeutic management. These can vary based on patient symptoms and risk profiles:

1. Start prophylactic-dose low-molecular-weight heparin on all patients admitted to the with suspected COVID-19 infection.
2. Consider a baseline non-contrast chest CT on all patients with suspected COVID-19 who have an indication for hospital admission.
3. For patients with suspected COVID-19 who also have a high clinical suspicious for pulmonary embolism, consider CT pulmonary angiography if the patient’s D-dimer level is elevated. If a pulmonary embolism is confirmed, therapeutic anti-coagulation is indicated.
4. For admitted patients, routine D-dimer testing both on admission and routinely throughout their stay should be considered for prognostic stratification with additional imaging as available.

• For patients with a D-dimer <1,000 µg/L on admission and no significant increase on follow-up, continue prophylactic anticoagulation.

• For patients with D-dimer <1,000 µg/L on admission, but with significant increase above 2,000-4,000 µg/L during their hospital stay, imaging for deep vein thrombosis or pulmonary embolism should be considered, especially when signs suggest clinically-relevant hypercoagulability, such as venous congestion or thrombosis present on chest CT, clotting of extracorporeal circuits, or when patients deteriorate. When imaging isn’t feasible, consider therapeutic-dose low-molecular weight heparin without imaging when the risk of bleeding is acceptable.

• For patients with D-dimer values between 1,000 and 2,000 µg/L, study authors only suggested instituting prophylactic anticoagulation. But, because these patients may suffer from venous thromboembolism, that should be excluded where possible.

• Use caution with patients with a strongly increased D-dimer on admission, such as 2,000-4,000 µg/L. Repeat D-dimer testing within 24 hours-to-48 hours to catch any increases. If levels rise, consider imaging for deep vein thrombosis or pulmonary embolism. 

Additional research has also revealed a link between COVID-19 and pulmonary embolism. In an additional letter published in Radiology from Hôpitaux Universitaires de Strasbourg, researchers reported that from 106 pulmonary CT angiograms performed on COVID-19-positive patients during one month, 32 patients (30 percent) had acute pulmonary embolus. Typically, 1.3 percent of critically ill patients without COVID-19 and 3 percent-to-10 percent of emergency patients develop a pulmonary embolism.

According to the study results, a D-dimer threshold of 2,660 μg/L identified all patients with pulmonary embolism on chest CT.

A second letter reinforced those findings. Results from Centre Hospitalier Universitaire de Besancon in France revealed 23 percent of COVID-19-positive patients had a pulmonary embolism show up on a chest CT with contrast. These patients were more likely to require mechanical ventilation and to require care in the critical care unit.

Ultimately, van Beek said, providers should remain vigilant and acutely aware that this virus is much more complicated than initially believed and its impact is further reaching.

“COVID-19 is more than a lung infection,” van Beek said. “It affects the vasculature of the lungs and other organs and has a high thrombosis risk with acute life-threatening events that require adequate treatment with anticoagulants based on laboratory monitoring with appropriate imaging tests as required.”