Covid is a blood vessel problem - Dont forget this
When Covid-19 first emerged, it was initially thought that – like other coronaviruses affecting humans – it mainly caused lung problems.
But as the outbreak progressed, case studies began to suggest that some of the most severe complications of the disease affected more than just the lungs. From reports of ‘sticky blood’ raising the risk of deep vein thrombosis, heart attack or stroke, to neurological effects, many complications seemed to be affecting the blood vessels.
In particular, these problems can be caused by the way that Covid-19 affects the lining of the blood vessels, called the endothelium. This layer of cells is not a solid barrier - it can allow or block certain substances from entering or leaving the bloodstream depending on conditions in the body. It also has a vital role in allowing our blood vessels to function normally.
A healthy, well-functioning endothelium helps to keep our blood vessels relaxed and open to the flow of blood. It also releases substances that help to prevent harmful blood clots and inflammation. But if the endothelium is damaged, these processes may not work effectively, which is known as ‘endothelial dysfunction’.
Endothelial dysfunction is a key factor in the development of heart and circulatory conditions. For example, it is linked to the formation of fatty plaques in our arteries, which can rupture, leading to heart attacks and strokes. There is evidence that endothelial dysfunction is linked to more severe forms of Covid-19.
While it's now thought that newer and now much more common variants of the virus (such as Omicron) may not impact the endothelium as much as previous variants, endothelial dysfunction likely also plays a role in the symptoms of long Covid.
How does coronavirus damage blood vessels?
Initially, researchers thought that SARS-CoV-2 (the virus causing Covid-19) may be able to directly infect the endothelium (the cells that line blood vessels). Another study discovered that ACE2, a molecule which acts as an 'entry gate' for the virus to enter the endothelium, is found in higher levels in lung endothelial cells of people who die from Covid-19. This study also showed a link between Covid-19 infection and damage to lung capillaries (the smallest type of blood vessel), which were more likely to have tiny blood clots inside them.
More recently, researchers are starting to understand that Covid-19 damages our blood vessels in a less direct way. For example, there is evidence that if SARS-CoV-2 gets into the lung epithelial cells (cells which help oxygen cross from the air into our bodies), it can trigger inflammation in nearby blood vessels. Studies have also found that when people have Covid-19, their immune system can react in a way that leads to damage of the blood vessels.
How might blood vessel damage lead to complications?
By triggering endothelial damage, coronavirus infection may cause abnormal blood clotting, ‘leaky’ vessels and reduced blood flow. These endothelial effects could have consequences from head to toe.
In the lungs, these effects can cause clots and fluid to accumulate, which means the lungs are less able to get oxygen into the body. In the brain, damage to endothelial cells in the blood-brain barrier could lead to inflammation. In the limbs, reduced blood flow could lead to ‘Covid toe’.
In September 2022, a study led by researchers from the BHF Data Science Centre examined the anonymised healthcare records of 48 million people living in England and Wales. They found that people who caught Covid-19 during the first wave of the pandemic (when vaccines were not yet available) had an increased risk of developing a clotting-related complication, such as heart attack or deep thrombosis, for almost a year after infection.
This link between Covid-19 and the effects it can have on the endothelium may help to explain why people with certain heart and circulatory conditions are at a higher risk of developing severe complications of Covid-19. If another condition, such as diabetes or high blood pressure, has already damaged the endothelium, the virus’s impact may be magnified.
While this sounds worrying, we already have many different treatments available to help limit blood clotting and improve circulation. Since the virus emerged, researchers have been learning more about how existing cardiovascular treatments can be applied to help limit the damaging effects of Covid-19.
Is long Covid a blood vessel problem?
There is growing evidence that long Covid could be linked to lasting damage to the endothelium (the lining of the blood vessels).
One study found that people with long Covid symptoms - especially people with fatigue, chest pain and cognitive symptoms - were more likely to have impaired endothelial function. They measured endothelial function by using a device which can calculate flow of blood to the fingers, and whether it responded normally to having a cuff inflated around the wrist. This link didn’t seem to be connected to other factors which are known to limit endothelial function, such as age, diabetes or coronary heart disease.
The study was based on 798 people in Tunisia who had recovered from Covid-19, 618 of whom had ‘long Covid’ symptoms. One limitation of this study was that it did not include a ‘control group’ of people who had not had Covid-19 to compare the measurements to. But similar smaller studies have also demonstrated that dysfunction of the endothelium can persist for at least several months after ‘recovery’ from Covid-19.
Further research is needed to better understand whether this persistent endothelial dysfunction is directly linked to lasting symptoms of Covid-19, but this also raises the possibility that existing treatments which can improve endothelial function (such as statins) could be used to help people who develop long Covid.
Can Covid cause blood clots?
Yes, one of the most serious complications of Covid-19 infection is the risk of developing dangerous blood clots in the blood vessels.
Research supported by the BHF, published in September 2022, has found that people who caught Covid-19 during the first wave of the pandemic (when vaccines were not yet available) had an increased risk of developing a blood clot for almost a year after infection.
The research found that in the first week after a Covid-19 diagnosis, the risk of conditions caused by blood clots in the arteries, such as a heart attack or stroke, was 21 times (2,100 per cent) higher compared to people without a Covid-19 diagnosis. By six months to a year after diagnosis, the risk had gone back down, although it remained higher than before the diagnosis – a 1.3 times (30 per cent) increase in risk.
Researchers also looked at other conditions that are caused by blood clots in the veins, such as deep vein thrombosis (DVT) and pulmonary embolism (a blood clot in a lung). The risk of blood clots in the veins was found to be 33 times (3,300 per cent) higher in the week after a Covid-19 infection compared to people without a Covid-19 diagnosis, dropping to 1.8 times (80 per cent) higher after 26 to 49 weeks.
There have been some anecdotal reports that clot-related complications may be less common in people with Covid-19 caused by more recent variants (such as Omicron), but there is a need for more research in this area before we can be sure.
How are coronavirus-related blood clots prevented?
Luckily, existing drugs can help prevent or limit blood clotting after Covid-19, including ones which have been safely used for many years.
Based on the current evidence, UK guidelines for the treatment of Covid-19 recommend that all people admitted to hospital with severe Covid-19 should, where possible and appropriate for the individual, receive the blood-thinning drug heparin to help prevent clotting complications.
Further research is being done to find out whether other drugs, such as aspirin, might also help. Unless it’s on medical advice, you shouldn’t start taking aspirin or any other blood thinner during or after Covid-19 infection. If you have coronavirus and are already prescribed a blood-thinner to manage your existing heart condition (such as aspirin or clopidogrel), keep taking it unless your doctor recommends otherwise.
We now understand much more about the damaging effects of Covid-19 on our blood vessels. We also have some promising avenues to explore to try to prevent this damage. For instance, protecting the endothelium from damage caused by Covid-19 in the first place could help to prevent clotting-related complications.
Early research shows that certain commonly used medications could do just that. In the UK, the HEAL-COVID trial is examining whether patients who have been hospitalised with Covid-19 benefit from taking the statin atorvastatin after being discharged from hospital. A Canadian trial is also testing whether ACE inhibitors or ARBs help people to recover from Covid-19, both in milder cases and those requiring a hospital admission. more