Dr. Clare Bryce and her team have performed about 100 autopsies on COVID-19 patients at New York’s Mount Sinai Health System, and in that time, she’s begun to notice some patterns.
Many of the deceased patients were showing evidence of unusual blood clots in their veins, said Bryce, who is Sinai’s associate director of autopsy service.
Some also had lung damage throughout the alveoli — the tiny air sacs branching through your lungs — and the lungs themselves were denser and heavier than normal.
“When I looked at the lungs at autopsy, they had a very different look to them,” she said. “In this case, the lungs had an interesting lumpy texture.”
This alveolar damage suggested that patients would have a hard time getting enough oxygen, she said.
And when the physicians examined tissue under a microscope, they saw tiny blood clots in the lungs, blood vessels and even the brain, where in some cases, the tissue surrounding the clot had died.
Elsewhere in the hospital, Dr. Johanna Fifi, director of the endovascular stroke program, also noticed problems with blood clots.
At the height of New York City’s outbreak, she said, “About 50 per cent of our large-vessel strokes tested positive for COVID-19.”
Fifi was part of a group of physicians who wrote a letter to the New England Journal of Medicine describing some of the cases they saw, some in patients who had none of the traditional risk factors for stroke.
The physicians at Mount Sinai aren’t alone in what they’re seeing. Several reports have pointed to a larger incidence of clots and stroke among COVID-19 patients compared to others, and physicians are trying to find out why – and how blood clotting contributes to the disease.
Many severely ill patients, not just COVID-19 patients, are at increased risk of blood clots, said Dr. Emily McDonald, a professor of medicine at McGill University.
“People who are sicker in general and admitted to the hospital already have a higher chance of having blood clots because of their own immune system and because they’re not moving as much and they may be bed-bound. That all increases your chance of blood clots,” she said.
But the problem seems worse with the coronavirus.
A recent paper published in JAMA Neurology compared rates of stroke among hospitalized COVID-19 patients to those of people hospitalized with influenza, and found that the COVID-19 patients were much more likely to have a stroke.
“Probably there’s something more going on related to the virus and the body’s immune response to the virus,” McDonald said.
That something, she said, could be an overblown immune response to the SARS-CoV-2 virus, predisposing people to clots.
Another theory is that the SARS-CoV-2 virus might directly attack the cells that line blood vessels, known as endothelial cells.
Bryce and her colleagues described endothelial damage in a non-peer-reviewed summary of their autopsy findings. Another group of researchers also described endothelial cell dysfunction in a letter to the Lancet.
“There’s a predisposition of the virus to affect the lining of the blood vessels, the endothelium. And I think this is kind of can explain one of the hallmarks that we see is that it’s kind of affecting blood vessels all over the body, not just causing strokes per se,” Fifi said.
It’s hard to say how common blood clots are in COVID-19 patients, McDonald said, simply because we’re only looking for them in severely ill patients who are going to the hospital — though tiny blood clots have been suspected of causing milder symptoms, like “COVID toes.”
“We might be even underestimating the degree to which there are blood clots in the simpler, less-sick cases, just because we don’t necessarily go and look for it,” she said.
It hasn’t been proven yet, McDonald said, but there is a theory that the virus may attach to receptors in the lining of blood vessels and directly infect endothelial cells, causing the damage.
The answers to how and why COVID-19 affects blood clots and blood vessels matter, she said.
“It’s offering us new potential options for treatment,” she said.
“So when we talk about it being a respiratory virus — in the lungs, you have blood vessels. And so when the virus attacks the lungs, there’s many different mechanisms by which it could cause what we see on the outside as lung problems.
“It could be that the oxygen level in people is decreased because they have tiny blood clots that are filling up the lungs.”
If that’s true, preventing clots could prevent some organ damage.
A Canadian-led international trial, known by the acronym ATTACC (Antithrombotic Therapy to Ameliorate Complications of COVID-19) that McDonald is contributing to, is examining whether doctors can improve patients’ chances of developing severe complications by giving them higher-than-usual doses of the blood thinner Heparin.
This trial, and other research examining how the SARS-CoV-2 virus affects the body, will change how doctors treat their patients, she said, but there is a lot left to learn.
“I think this question keeps coming up with COVID: how much of it is the virus and how much of it is your immune system’s response to the virus, which seems to be giving us all kinds of kind of funny complications?”
Questions about COVID-19? Here are some things you need to know:
Symptoms can include fever, cough and difficulty breathing — very similar to a cold or flu. Some people can develop a more severe illness. People most at risk of this include older adults and people with severe chronic medical conditions like heart, lung or kidney disease. If you develop symptoms, contact public health authorities.
To prevent the virus from spreading, experts recommend frequent handwashing and coughing into your sleeve. They also recommend minimizing contact with others, staying home as much as possible and maintaining a distance of two metres from other people if you go out. In situations where you can’t keep a safe distance from others, public health officials recommend the use of a non-medical face mask or covering to prevent spreading the respiratory droplets that can carry the virus.
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