Similar to previous strains of coronavirus (SARS, MERS), research suggests that COVID-19 can cause serious vascular complications. The most common vascular issues include deep vein thrombosis (DVT), pulmonary emboli and acute limb ischemia (ALI). Exactly how COVID-19 causes these complications is not well understood; however, all of these conditions are associated with abnormal blood clotting.
The process of blood clotting (thrombosis) depends on three factors:
- Endothelial injury
- Venous stasis
- Hypercoagulable state
Blood vessels are lined with a thin layer of tissue known as endothelium. Under normal conditions this lining helps blood flow smoothly throughout the body. Injury to this layer can occur in several ways including physical punctures, inflammation, hypertension, and shear wall stress.
When the endothelium is damaged, deeper layers of the vessel become exposed to the blood. Exposure of these deep layers triggers a stepwise series of reactions referred to as a clotting cascade. The purpose of this cascade is to prevent blood loss at the site of injury and to promote healing of the damaged vessel.
Some researchers believe that COVID-19 may cause direct injury to the vascular endothelium. Others believe that endothelial injury may be secondary to inflammation from the body’s immune response to the virus. Either way, it appears that COVID-19 can cause abnormal activation of the clotting cascade, resulting in thrombosis and vascular ischemia.
When muscles in the arms and legs contract, neighboring veins are compressed and blood is pushed back towards the heart. During periods of inactivity it is difficult for blood to flow back to the heart because these muscles are not being used. This most commonly occurs with lengthy travel or extended hospitalizations.
Prolonged muscle inactivity leads to the accumulation of blood in the extremities, known as venous stasis. Stasis contributes to clotting because blood has a tendency to thicken and clot when flow is disrupted. This is exactly what happens when blood starts to pool in the extremities.
Individuals hospitalized for severe COVID-19 infection are at an increased risk for venous stasis due to limited mobility. Fortunately, hospitals frequently use several strategies to reduce this risk. These strategies include the use of blood thinning medication, compression socks and pneumatic compression devices.
Normally, blood remains a fluid inside the body. It will not clot unless specific conditions (such as those discussed above) are met. A hypercoagulable state occurs when blood begins clotting spontaneously, independent of these conditions. Hypercoagulability is sometimes the result of genetic mutations, but it often occurs secondary to medications (e.g., hormone therapy), toxins (e.g., smoking) or diseases (e.g., cancer, systemic infection). These secondary triggers cause hypercoagulation by altering the concentration of clotting factors in blood. Unsurprisingly, researchers studying COVID-19 have found elevated levels of several different clotting factors in the blood of infected individuals. Increased concentration of these clotting factors suggests that COVID-19 is capable of promoting a hypercoagulable state, thus increasing the risk of thrombus formation and vascular injury.
Vascular complications due to COVID-19 are uncommon, but it is important to recognize the warning signs. Associated vascular complications usually occur in the extremities, with the majority affecting the legs. Classic symptoms of limb clotting and ischemia include:
- Pain in the affected limb
- Loss of a palpable pulse
- Abnormal paling of the skin
- Limb numbness and/or paralysis
- Coolness/sudden loss of warmth
Obesity, advanced age, or pre-existing heart disease increase your risk of vascular complications; however, clotting and ischemia have also been observed in individuals without these conditions. If you or someone you know has been infected with COVID-19 and starts experiencing these symptoms, seek immediate medical evaluation. Acute limb ischemia is a serious condition that can lead to necrosis and
limb loss if left untreated. Additionally, limb clotting can lead to other serious conditions such as pulmonary embolism and stroke. Diagnoses of limb ischemia can usually be made in a medical office with non-invasive imaging studies. Once diagnosis is confirmed, most patients are started on anticoagulation therapy. In severe cases, treatment may also include revascularization of the limb with an endovascular or open surgical procedure by a licensed vascular surgeon.