Doctors and scientists are still working to understand why COVID-19 can cause fatal damage to so many different organs. A potentially major piece of that puzzle was revealed today in research published in the Journal of the American Heart Association.
During the COVID-19 pandemic, hospitalized patients who weren’t sick enough to be in the intensive care unit would suffer heart attacks and strokes, said William T. Bain, MD, a critical care pulmonologist at the University of Pittsburgh and the study’s senior author.
The deaths distressed and confounded clinicians, explained Bain. These patients didn’t seem to be in immediate danger. Occasionally, a heart attack or stroke happened in someone who appeared to be getting better, including those who seemed well enough to be sent home.
“This often affects younger populations, sort of in patients in their 40s and 50s,” he said.
In search of a biological explanation, Bain and his team examined blood samples from 93 patients who were enrolled in a National Institutes of Health–backed randomized trial launched during the pandemic.
This often affects younger populations, sort of in patients in their 40s and 50s.
They found a striking association. People were more likely to develop clots and die if the SARS-CoV-2 virus had spread to their bloodstream.
Clearer picture of the pathophysiology
Specifically, the researchers linked clotting and viremia, or the presence of virus in the bloodstream, to soluble thrombomodulin.
Thrombomodulin is a protein on the surface of the cells that line the inside of blood vessels. The protein becomes soluble when viremia causes the proteins of the cellular lining to break off.
This may happen even as the COVID infection in the lungs improves.
Bain and his colleagues theorize that viral damage to cleaved thrombomodulin creates clots, which then travel throughout the body and fatally disrupt blood flow.
“So that could be stroke, it could be heart attack, it could be what’s called a venous thromboembolism, which can go to the lungs and cause a pulmonary embolism,” said Bain. An embolism is a life-threatening blockage in a lung artery, usually a clot.
To be clear, Bain doesn’t claim this link is the only reason clotting occurs in COVID patients. But he said it helps build a more detailed understanding of why so many people died.
Filling a key knowledge gap
The scientists behind this study should be applauded for their work, because the mechanisms that link COVID-19 and blood clotting are a key gap in medical knowledge, said Tim Plante, MD MHS, a cardiovascular disease epidemiologist and internal medicine physician at the University of Vermont.
“This is a rather remarkable study,” he said.
The association is novel and presents very interesting insights, added Alok A. Khorana, MD, a researcher at the Cleveland Clinic and chair of the National Blood Clot Alliance’s medical and scientific advisory board.
This is a rather remarkable study.
If this relationship is confirmed, Anok said interventions like blood thinners could be prescribed earlier to prevent clots from forming.
Plante and Khorana did not contribute to the study. Nor did Philip Norris, MD, an infectious diseases physician at the University of California, San Francisco, and vice president of research at Vitalant Research Institute.
To prove the existence of a causal relationship, not just an association, Norris said scientists would have to do additional experiments.
Also, now that most people have COVID-19 antibodies from vaccination and previous infection, future research is needed to determine whether there is still an association between blood clots and viremia.
Still, Norris said the study indicates that, “Clearly our best prognostic marker for complications of SARS-CoV-2 infection is the presence of viremia.”
Beyond COVID-19
Though scientists studied only COVID patients, Bain said the findings could benefit people sickened by other respiratory viruses, including influenza, respiratory syncytial virus (RSV), and hantavirus, which also have a higher risk of stroke and heart attack.
Also, while COVID-19 has passed the pandemic stage and is now endemic, Plante noted that it is the second global public health emergency caused by a SARS virus in the past 25 years.
There’s always a risk of a new, novel SARS virus causing another pandemic.
In 2002, a new SARS virus that caused severe pneumonia was identified in Guangdong province, China. The disease, severe acute respiratory syndrome, spread to 28 other countries and killed at least 916 people.
“There’s always a risk of a new, novel SARS virus causing another pandemic,” warned Plante. “This study helps us better understand the mechanisms behind COVID-19 disease and makes us better ready to take on future pandemics.”
