What We Know (and Do not Know) Regarding the Pathogenesis of Pulmonary Thrombosis in COVID-19

Epidemiology and Predisposing Factors of Post-COVID Venous Thrombosis: A Concise Review

Long-coronavirus disease 2019 (COVID-19) represents a heterogeneous clinical syndrome characterized by a pathologic continuum of signs, symptoms, and also laboratory/radiologic abnormalities that may persist for a long time after recovering from an acute severe acute respiratory syndrome-coronavirus disease 2 infection. Among the various components of this postviral condition, the risk of venous thromboembolism in patients hospitalized for COVID-19 remains considerably higher after discharge, especially in older individuals, in men, in patients with longer hospital stays and more aggressive treatment (e.g., mechanical ventilation and/or intensive care), when thromboprophylaxis is not used, and in those with a persistent prothrombotic state. Patients who have these predisposing factors should be monitored more closely to intercept any thrombosis that may occur in a post-COVID time-related manner but may also benefit from extended thromboprophylaxis and/or antiplatelet therapy.

In Situ Pulmonary Arterial Thrombosis: Literature Review and Clinical Significance of a Distinct Entity

Filling defects identified in the pulmonary arterial tree are commonly presumed to represent an embolic phenomenon originating from thrombi formed in remote veins, particularly lower-extremity deep venous thrombosis (DVT). However, accumulating evidence supports an underappreciated cause for pulmonary arterial thrombosis (PAT), namely, de novo thrombogenesis-whereby thrombosis arises within the pulmonary arteries in the absence of DVT. Although historically underrecognized, in situ PAT has become of heightened importance with the emergence of SARS-CoV-2 infection. In situ PAT is attributed to endothelial dysfunction, systemic inflammation, and acute lung injury and has been described in a range of conditions including COVID-19, trauma, acute chest syndrome in sickle cell disease, pulmonary infections, and severe pulmonary arterial hypertension. The distinction between pulmonary embolism and in situ PAT may have important implications regarding management decisions and clinical outcomes. In this review, we summarize the pathophysiology, imaging appearances, and management of in situ PAT in various clinical situations. This understanding will promote optimal tailored treatment strategies for this increasingly recognized entity.

Autoimmune Diseases Affecting Hemostasis: A Narrative Review

Hemostasis reflects a homeostatic mechanism that aims to balance out pro-coagulant and anti-coagulant forces to maintain blood flow within the circulation. Simplistically, a relative excess of procoagulant forces can lead to thrombosis, and a relative excess of anticoagulant forces can lead to bleeding. There are a wide variety of congenital disorders associated with bleeding or thrombosis. In addition, there exist a vast array of autoimmune diseases that can also lead to either bleeding or thrombosis. For example, autoantibodies generated against clotting factors can lead to bleeding, of which acquired hemophilia A is the most common. As another example, autoimmune-mediated antibodies against phospholipids can generate a prothrombotic milieu in a condition known as antiphospholipid (antibody) syndrome (APS). Moreover, there exist various autoimmunity promoting environments that can lead to a variety of antibodies that affect hemostasis. Coronavirus disease 2019 (COVID-19) represents perhaps the contemporary example of such a state, with potential development of a kaleidoscope of such antibodies that primarily drive thrombosis, but may also lead to bleeding on rarer occasions. We provide here a narrative review to discuss the interaction between various autoimmune diseases and hemostasis.