‘New Mechanism For Stroke?’: Blood clotting in Coronavirus patients has experts looking at role of viruses in causing stroke
A growing body of evidence is painting a grim picture of how coronavirus can wreak havoc from one end of the body to the other.
It’s well established that COVID-19 affects the respiratory system and targets the lungs. But several studies and anecdotal evidence suggest the disease may also cause super-charged blood clotting that damages vital organs, including the kidneys, heart and brain.
The New England Journal of Medicine recently published a case report on a small cluster of strokes in New York that involved young, healthy people, who had the virus but no known risk factors for stroke.
But strokes, where a clot blocks blood flow to the brain, appear to be just one way damage from clotting can play out in COVID-19 patients.
There are also reports of ‘COVID toes’ – painful red inflammations of the feet linked to blood clots.
Then there is the widely reported story of 41-year-old Broadway actor Nick Cordero, whose right leg was amputated after he developed severe blood clots while he was in hospital being treated for coronavirus.
‘New mechanism for stroke’
Some experts suggest that what’s going on may represent an entirely new way in which blood clots can form.
It might be the case that viruses generally have a more direct role in causing strokes than has been previously thought, says an Australian doctor working on the frontline against COVID-19 in New York.
“We are asking ourselves… have we just discovered a new mechanism of stroke?” says Associate Professor Thomas Oxley, Interventional Neurologist at New York’s Mt Sinai Hospital, where thousands of COVID-19 patients have been treated.
Strokes kill brain cells and are a major cause of death and disability. They can cause changes in language, mood, vision and movement. In up to 30 per cent of strokes, the cause is unknown.
Dr Oxley says there is some evidence the clotting leading to strokes and other issues might be being triggered directly by an interaction between the virus and the blood vessel wall.
“I’m a stroke neurologist but we don’t usually think about viral infection as a cause for stroke. That [idea] is something very new in medicine.”
The role of blood clots
Dr Oxley says the links coming to light between the virus and blood clotting show the virus is affecting the body’s blood system, as well as the respiratory system.
“Up to this point, we’ve been focusing on pneumonia as the primary problem caused by COVID-19,” Dr Oxley says. Pneumonia is when the tiny air sacs in the lungs become full of fluid, making it hard to breathe.
“We are now learning there is another major cause of disease by COVID and it’s got to do with the formation of blood clots.”
Among the problems doctors around the world have been reporting are an increase in clots in the deep veins of the legs (known as deep vein thrombosis or DVT) and the lungs (pulmonary embolisms).
Around one in four people with coronavirus who end up in intensive care will develop a pulmonary embolism, while the incidence of clots in the deep veins of the legs or in the lungs is 30 to 70 per cent.
The same underlying problem is thought to be behind an increased number of strokes observed in multiple medical centres in New York and other COVID-19 hot spots around the world.
The New York stroke cluster observed by Dr Oxley’s team was especially worrying as it involved young, healthy people who were at home with only mild COVID-19 symptoms. But they suddenly developed signs of stroke in large blood vessels in their brains.
The pattern of abnormal blood clotting is being recognised as a new phenomenon doctors are calling ‘COVID-19-associated coagulopathy’ or CAC.
Dr Oxley says that following concerns by a consensus of doctors, Mount Sinai Hospital has just changed its treatment guidelines for COVID-19 patients.
It is now recommending all new patients coming to intensive care with the disease be given more aggressive treatment with so-called “blood thinning” medication to reduce clot risk.
“What we’re learning is coming out so quickly, it’s putting pressure on everyone to get their heads together,” Dr Oxley says.
“I think there is now enough evidence to support the idea that a major mechanism of the virus causing disease is through blood clots.”
How blood clots cause harm
It’s thought blood clots cause damage in multiple ways.
In the lungs, it seems clots can interfere with blood flow in small blood vessels, preventing oxygen passing from the lungs to the blood.
As intensive care specialist Professor Hugh Montgomery, from University College London, told 7.30: “Blood essentially is coming into the lung full of carbon dioxide and without much oxygen and it is transiting the lung… in exactly the state that it came in.”
Professor Bruce Campbell, head of stroke neurology at Royal Melbourne Hospital, says there haven’t yet been reports of strokes linked to COVID-19 in Australia, but that this might be simply because of the much smaller number of COVID-19 cases here.
“Our concern is more that people [in Australia] with stroke symptoms are avoiding or delaying coming to hospital for fear of [catching] the virus,” he says.
Understanding causes of blood clots
The reason for the blood clotting problems in COVID-19 is not known.
In severe cases of COVID-19, possible causes include underlying medical conditions, being immobile, and an abnormal immune reaction known as a “cytokine storm”.
But the risk of clots in COVID-19 generally is significantly greater than what is usually seen in patients in hospital and intensive care units.
Since strokes occurred even in young healthy people with COVID-19, Dr Oxley thinks a process where the virus attacks the lining of blood vessels, causing local inflammation, that could then trigger clots, might be another option.
He said a recent article in the medical journal The Lancet supported this idea. It showed the virus attached to lock and key mechanisms, known as ACE2 receptors, on the inner walls of blood vessels of patients.
“It’s is mind blowing to think the virus could directly cause blood clots,” said Dr Oxley, adding what is being seen could represent an entirely new mechanism of disease.
“The broader question is how much don’t we know about viruses yet? And how will it change future practice moving forward?”
Professor Huyen Tran, who specialises in blood disorders and is on Australia’s COVID-19 National Clinical Evidence Taskforce, says he did not think there was enough evidence yet to recommend Australian hospitals follow the changed guidelines started at New York’s Mt Sinai Hospital.
But the benefits of more aggressive treatment to prevent blood clots in critically ill COVID patients is being studied in a trial in Italy.