People infected with the new coronavirus have a higher risk of blood clots and stroke. How much do we currently know?

People infected with the new coronavirus have a higher risk of blood clots and stroke. How much do we currently know?

Core tip: In addition to causing serious breathing problems, more and more evidence shows that COVID-19 can cause abnormal blood clotting. Patients with severe COVID-19 infection seem to be more likely to form blood clots in veins and arteries.　　In addition to causing serious breathing problems, there is increasing evidence that COVID-19 can cause abnormal blood clotting. Patients with severe COVID-19 infection seem to be more likely to form blood clots in veins and arteries.

　　Thrombosis occurs deep in the veins of the legs (deep vein thrombosis) and can be transferred to the lungs, causing a pulmonary embolism, which blocks blood flow and oxygen, and poses a fatal risk. Among them, when blood clots in the arteries obstruct the blood supply to the heart, it will cause a heart attack; when the blood clots prevent the oxygen supply to the brain, it will cause a stroke.

　　So, why do coronavirus patients have blood clots, and how can they treat or prevent such complications?

The latest data from the Netherlands and France show that 30-70% of coronavirus patients treated in the ICU have thrombosis in the deep veins of the thighs or in the lungs. Approximately a quarter of patients entering the ICU will have pulmonary embolism. This proportion is much higher than that of patients who need to enter the ICU for other reasons.

　　COVID19 patients have a higher risk of stroke

　　Compared with the general population, patients admitted to hospital for COVID-19 are also more likely to have stroke symptoms. Generally, the risk of stroke is related to aging and other risk factors such as high blood pressure, elevated cholesterol levels or smoking.

　　The oxygen content in COVID19 patients is too low

　　COVID-19 also seems to be related to thrombosis in capillaries, which is very important for the supply of oxygen inside tissues and organs. The test report shows that SARS-CoV-2 infection is present in the vascular endothelial cells in the lungs, kidneys and intestines of patients with COVID19, which may cause tiny thrombi to appear in the capillaries in these parts, thereby interfering with normal blood flow and The blood's ability to deliver oxygen to these organs.

　　In addition, these small blood clots may reduce normal lung function. This explains why the oxygen levels in severely ill patients with COVID-19 are very low.

　　The treatment and diagnosis of thrombus is very difficult

　　When a patient is admitted to the hospital for treatment due to coronavirus (or other reasons), the usual treatment is to use a small dose of blood thinner to prevent the formation of blood clots. However, given that COVID-19 patients are more prone to thrombosis, it is currently being discussed whether a higher dose of blood thinner is needed to prevent these thrombotic complications.

　　In addition, the diagnosis of thrombosis in COVID-19 patients is also very difficult. First, it is not easy to distinguish the symptoms caused by pulmonary embolism and viral infection. Second, the SARS-coV-2 virus can interfere with the accuracy of laboratory tests for venous thrombosis. A good example is the D-dimer test, which measures blood clotting in the body. Under normal circumstances, almost all patients with venous thrombosis will have a high test index. However, for patients with severe COVID19 infection, their D-dimer levels will also increase significantly. Therefore, for these patients, the test is not suitable for the diagnosis of thrombosis.

　　Why does COVID-19 cause blood to clot?

　　One theory is that the increase in blood clots caused by COVID-19 infection may be caused by the patient's physical abnormalities and inability to perform normal activities. However, current data show that the blood clotting risk of COVID-19 patients is significantly higher than that of hospitalized and ICU patients, so it cannot be fully explained. Another possible explanation is that the virus directly affects blood vessel wall cells. When the body fights infection, the immune system is activated to kill the virus. Studies have shown that an activated immune system can cause blood clots. In severely ill patients with COVID-19, the immune system seems to be over-activated. This may lead to the production of a large number of over-activated immune cells, which eventually leads to the formation of blood clots. Another possibility is that the virus itself triggers blood clotting, which makes it better for survival.

　　Preliminary studies have shown that heparin, a commonly used blood thinner, can bind to SARS-CoV-2 and inhibit the key protein that the virus invades the human body, thereby having an antiviral effect.

　　In short, due to the continuation of the COVID-19 epidemic, the number of thrombotic complications is also increasing rapidly. We still need to learn more about the virus in order to find the best way to prevent and treat the above complications. (Bioon.com)

　　Reference materials:

　　1. People with coronavirus are at risk of blood clots and strokes. Here's what we know so far. The conversation

　　2. Explainer: what is deep vein thrombosis? The conversation

　　3. FA Klok et al., Incidence of thrombotic complications in critically ill ICU patients with COVID-19 2020. Thrombosis Research, 191: 145-147

　　4. Large-Vessel Stroke as a Presenting Feature of Covid-19 in the Young. N Engl J Med 2020; 382: e60 DOI: 10.1056/NEJMc2009787

　　5. Coronavirus'cytokine storm': this over-active immune response could be behind some fatal cases of COVID-19. The conversation

　　6. Lanying Du et al., Cleavage of spike protein of SARS coronavirus by protease factor Xa is associated with viral infectivity, Biochemical and Biophysical Research Communications. 2007. 359(1): 174-179,