Pulmonary Thrombosis and Thromboembolism in COVID-19

Abstract

COVID-19, the disease responsible for the devastating pandemic that began at the end of 2019, has been associated with a significantly increased risk of pulmonary thrombosis, even in patients receiving prophylactic anticoagulation. The predilection for thrombosis in COVID-19 may be driven by at least two distinct, but interrelated, processes: a hypercoagulable state responsible for large-vessel thrombosis and thromboembolism and direct vascular and endothelial injury responsible for in situ microvascular thrombosis. The presence of pulmonary thrombosis may explain why hypoxemia is out of proportion to impairment in lung compliance in some patients with COVID-19 pneumonia. Because pulmonary embolism (PE) and COVID-19 pneumonia share many signs and symptoms, diagnosing PE in patients with COVID-19 can be challenging. Given the high mortality and morbidity associated with severe COVID-19 and the concern that aspects of the disease may be driven by thrombosis, many hospital systems have instituted aggressive anticoagulation protocols above standard VTE prophylaxis. In this review, the epidemiologic and pathophysiologic features, diagnosis, and treatment of COVID-19 pulmonary thrombosis and thromboembolism are discussed.

Keywords: COVID-19; VTE; anticoagulation; immunothrombosis; pulmonary embolism.

Figure 1

Illustrations demonstrating two different mechanisms for pulmonary thrombosis in COVID-19, which include large-vessel occlusion resulting from thromboembolism and microvascular in situ immunothrombosis resulting from direct vascular and endothelial injury. NET = neutrophil extracellular trap; vWF = von Willebrand factor.

Figure 2

Illustration showing how concomitant vasodilation can mitigate the hemodynamic effects of pulmonary thrombosis. A, Normal pulmonary vasculature. B, Pulmonary thrombosis, which increases pulmonary vascular resistance and leads to increased PA pressure. C, Concomitant pulmonary vasodilation potentially can “cancel out” the increases in pulmonary vascular resistance and PA pressure caused by pulmonary thrombosis. PA = pulmonary arterial.

Figure 3

Risk-stratification algorithm and treatment strategy, adapted from the European Society of Cardiology Guidelines. Reperfusion therapy includes thrombolysis and embolectomy. PE = pulmonary embolism; PESI = pulmonary embolism severity index; RV = right ventricular; SBP = systolic BP.