COVID-19: Why blood clots are a leading cause for coronavirus deaths

COVID-19 is a respiratory disease. But reports reveal that the new coronavirus is also killing people by ravaging the circulatory system.

Blood clotting is one of the severe complications arising from a SARS-CoV-2 infection, suggesting that it’s not just a lung disease. The British Heart Foundation says the coronavirus has been found to increase the risk of blood clotting, leading to cardiovascular problems and organ failure in some patients. This is more apparent among people with underlying medical issues such as diabetes, obesity, or high blood pressure.

Clots raise the chances of deep vein thrombosis, heart attack or stroke. Some reports link the effects of COVID-19 to neurological issues, painful red and swollen areas on the feet (termed ‘COVID toe’).

“Clotting seems to be a very prominent feature of this disease [COVID-19],” Johanna Fifi, a neuroendovascular surgeon and an author of an article in the New England Journal of Medicine.

“This is causing more thrombosis than any other virus,” says Pascal Jabbour, a physician at Thomas Jefferson University Hospital, Pennsylvania. “We’ve never seen that before.”

Platelets are crucial to blood clotting. COVID-19 has been found to alter platelets leading to heart attacks, strokes, and other severe complications in some patients, according to researchers at the University of Utah. Other studies suggest that a coronavirus infection can create a hormone imbalance, leading to blood clots.

Growing evidence points to damages to blood vessels in COVID-19 patients with no symptoms of stroke or blood clots. They seemed to have an elevated blood marker (D-dimer) that’s linked to blood clots. Some reports say clots occur in patients despite using standard blood-thinning drugs.

What’s blood clotting?

Blood clotting, or coagulation, prevents excessive bleeding during injuries. When a blood vessel wall breaks during injuries, blood cells called platelets work with proteins in blood plasma (the clear liquid) to form a clot over the wound to staunch bleeding. The process is called haemostasis, which is the body’s normal response to an injury.

Blood clotting involves a series of steps: Narrowing (constriction) of blood vessels; triggering the activity of platelets; proteins in blood plasma signal each other to set off a chain reaction; the proteins work with platelets to help build a net and create the blood clot. During the process, a small amount of blood change from a liquid to a semisolid state as platelets transform from a flat disk to a ball and come together to form a plug.

Why some blood clots can be dangerous

Clots are generally formed to prevent blood loss during injuries. When clots form inside blood vessels without an obvious injury or do not dissolve naturally, it can be dangerous. This pathological clot formation is called thrombosis.

Large blood clots in arteries can block the flow of oxygenated blood from the heart, and this can deprive a part of the body critical supplies of oxygen and nutrients. An abnormal clot in a vein (that carries deoxygenated blood) may hamper the return of blood to the heart, causing pain and swelling near the clot.

Depending on the site of the clot, thrombosis can result in heart attack, stroke or deep vein thrombosis (DVT).

What are the major blood clot issues?

The blood circulatory system is made up of vessels called veins and arteries, and they help transport blood throughout your body. Arteries carry oxygenated blood from the heart to other parts of the body, and veins transport deoxygenated blood to the heart.

Infections and inflammatory diseases increase the risk of developing blood clots or thrombosis. A blood clot in an artery is called arterial clot, a clot in a vein is termed venous clot. Clots can travel through the bloodstream, resulting in life-threatening situations.

The following are some of the critical issues listed by the American Heart Association:

■ Deep vein thrombosis: During DVT, the clot is found in a major vein inside your body. The lower part of the leg is a common site, but it can also happen in arms, pelvis, lungs, liver, intestines, kidneys, or even the brain. DVT in the lower limb can result in severe leg pain, difficulty walking, or even the loss of a limb.

■ Pulmonary embolism: It occurs when a blood clot that travels to the lungs. Common symptoms include sudden shortness of breath, chest pain, rapid heart rate and coughing up blood.

■ Heart attack: If a clot blocks a coronary artery (which supplies blood to the heart), a section of the heart muscle will be damaged due to lack of oxygen as the cells begin to die. This will lead to a heart attack. Heaviness in the chest, lightheadedness and shortness of breath are among the possible symptoms.

■ Stroke: A stroke can occur if a clot restricts blood flow to your brain. It will lead to the death of brain cells, impairing parts of the body that the cells control. A stroke can result in brain damage, long-term disability, paralysis, and even death. Symptoms include sudden and severe headache, sudden difficulty speaking or seeing.

■ Kidney failure: A blood clot in the kidneys can result in the malfunctioning of the kidney. When it happens, kidneys won’t be able to remove fluids and waste from the body.

How hormone imbalance triggers blood clots

Potentially deadly blood clots in COVID-19 patients can be caused by a hormone imbalance triggered by coronavirus infection. When the coronavirus, SARS-CoV-2, invades the body, it uses angiotensin converting enzyme 2 (ACE2) as a doorway to enter the cells. The process deactivates the enzyme that helps in balancing the key hormones. The hormone imbalance thickens the blood, resulting in clots.

The ACE2 can be found on the surface of endothelial cells, the lining of the blood vessels that regulate clotting. The British Heart Foundation says COVID-19 affects the endothelium, the layer that plays a vital role in allowing blood vessels to function normally. It acts like a check-post, besides releasing substances that prevent harmful blood clots and inflammation. If this lining is damaged, these processes may not work well, resulting in endothelial dysfunction.

“Endothelial damage is a central component in the entire spectrum of COVID-19 disease,” Dr Alfred Lee, associate professor of medicine at Yale Cancer Centre, says.

Some markers of endothelial cell and blood platelet activation have been found be nearly twice as high in the ICU patients compared to those not in the ICU, researchers say in a report in the journal The Lancet Haematology.

How coronavirus damages blood platelets

Proteins produced during COVID-19 infections make the platelets “hyperactive”, resulting in potentially deadly blood clots, researchers at the University of Utah have found. This hyperactivity triggers the onset of heart attacks, strokes and other complications.

Researchers also believe the platelets interfere with the action of other infection-fighting cells, making the infection worse.

“We found that inflammation and systemic changes, due to the infection, are influencing how platelets function, leading them to aggregate faster, which could explain why we are seeing increased numbers of blood clots in COVID patients,” Robert A. Campbell, assistant professor in the Department of Internal Medicine, at the University of Utah, says in a report in Blood, an American Society of Hematology journal.

Blood clots are a major killer of COVID-19 patients

Pneumonia caused by acute respiratory distress syndrome is a leading cause for COVID-19 deaths. Emerging evidence suggests that blood clots are also responsible for a large number of coronavirus-related fatalities. Clots have been found in the lungs and kidneys, while some patients suffered strokes.

“We did a very large post mortem series [in London] which showed very clearly that every patient we looked at had evidence of thrombosis somewhere,” Graham Cooke, an infectious disease specialist at Imperial College London, told a webinar for the Royal Society of Medicine.

In a study published in Lancet in May, the researchers showed that the disease is linked to the formation of tiny clots within capillaries (the smallest blood vessels) in the lungs. “There were nine times as many of these clots in people with COVID-19 as in the lungs of people who died from flu,” they said.

The following are some of the organs that can be severely impacted by a coronavirus infection:

■ Lungs: In the deceased COVID-19 patients, the blood clots appeared to have formed within the lungs, while more typically they would form elsewhere, break off and end up in the lung, according to the British Journal of Haematology.

■ Brain: A blood clot in an artery around the brain can trigger a stroke. The observations of study at the Thomas Jefferson University in Philadelphia, published in the journal Neurosurgery, suggests that young COVID-19 patients with no other risk factors for stroke have an increased risk, even if they do not have symptoms of the disease,

■ Kidneys: Critically ill COVID-19 patients can suffer from kidney damage, even if they don’t have kidney issues before contracting coronavirus. Blood clots can clog the tiny blood vessels in the kidneys, reducing their ability to function. In some people, the damage is so severe that they require dialysis, the Medical News Today says.

■ Legs: Life-threatening blood clots have been found in the arteries of the legs of COVID-19 patients, according to a study published in Radiology journal. Researchers said the patients with symptoms of inadequate blood supply to the lower limbs tend to have larger clots and a very high rate of amputation and death than uninfected people with the same condition.

■ Other parts of the body: Deep vein thrombosis was found in almost 60 persons of patients who died from COVID-19. DVT can occur in a leg or an arm, pelvis, liver and intestines.

Why blood clots can be fatal for COVID patients

Sol Schulman, a US haematologist, who studied the connection between COVID-19 and strokes, says the extensive damage to the lining of blood vessels may be the result of the overreaction from the immune system as the body tries to eliminate the virus.

The immune system, he says, is linked to the blood clotting system. So clotting is the body’s immune response to erect a barrier to invading pathogens. And an immune overreaction releases proteins that regulate blood clotting. The clots can travel to other parts of the parts resulting in strokes, heart attacks, kidney failures, and other complications.

This may also explain the discoloured “COVID toes” as well as the inflammatory reaction seen in some children, similar to a disease called Kawasaki Syndrome, a Bloomberg report says.

Evidence from researches around the world indicates that COVID-19 can trigger blood clots in an estimated 30 per cent of critically ill patients. And these clots have emerged as a leading cause of deaths in COVID-19 patients.