Sun. Sep 25th, 2022
Image of small blue spheres surrounded by long green fibers.
enlarge A fluorescent image of cardiomyocytes in culture.

Coronaviruses mainly spread through material released during breathing and cause respiratory symptoms. And SARS-CoV-2, part of its name coming from “severe acute respiratory syndrome,” seemed to be no exception. But as time went on, additional symptoms became apparent — loss of smell, digestive tract problems — and these probably weren’t due to a respiratory infection. And over time, it also became clear that the symptoms didn’t necessarily go away once the virus was gone.

As we’ve studied the virus more, we’ve learned that the protein it uses to attach to cells is present in many different tissues in the body, suggesting that a wide variety of different effects may be the direct product of infections. of the cells there. This week, the effect that seems to be drawing attention is heart problems, spurred on by a Scientific American article that covers (among other things) the stories of professional and college athletes who have been infected. That was followed by a report that about 30 percent of college athletes who contract the virus eventually develop an inflammation of the heart muscle called myocarditis — a number ESPN now says is a accidental exaggeration

Both reports contain many anecdotes, but this is not new; ESPN had reported myocarditis in college athletes in early August. And, most importantly, the scientific community has been investigating the matter for months. So far, the conclusion is that there are likely to be cardiac complications, even in patients with mild COVID-19 symptoms. But the long-term consequences of these problems are not yet clear.

Problems for the heart

One of the first indications of a potential problem came all the way back in March, courtesy of researchers in Wuhan who tracked some of the first COVID-19 patients. In their study, about 20 percent of a group of 416 hospitalized patients had some evidence of heart problems. The researchers used several blood tests to look for proteins that are normally found in heart muscle cells, but can be released into the blood when those cells become damaged. (For an example of one of the tests the Wuhan researchers used, see this description of the troponin test commonly used to check for heart problems.)

The researchers only managed to hook 14 of the individuals on an EKG to monitor the heart’s electrical activity during the period when these tests suggested there might be problems. However, all 14 showed abnormal heart rhythms.

Though suggestive, that was largely where things stood for several months. That changed in July, when a German group reported MRI imaging of a cohort of 100 patients diagnosed with SARS-CoV-2 infection. The median age of these patients was only 49 years, meaning they were much younger than the group considered to be at high risk for COVID-19 complications. And the group had already recovered from the virus (two-thirds without hospitalization), suggesting that whatever emerged was due to an ongoing problem rather than a direct impact of an ongoing infection.

Yet there were still problems. Seventy-one percent of patients showed signs of heart problems using the protein test linked above. And in 78 percent of them, MRIs often showed problems with the heart tissue itself, with inflammation being the most common symptom. None of the problems correlated with time since diagnosis, suggesting that these problems may persist for a while after the infections are cleared.

What’s wrong?

While there was evidence of some cardiac involvement, the reasons for the problem were much less clear. Difficulty breathing can cause the heart to work harder, which can exacerbate any underlying conditions. And COVID-19 appears to trigger an inflammatory response, which can involve the heart even without the organ being directly infected. But the fact that younger people with mild symptoms also seemed to have problems makes these explanations less likely. And a study from late July used heart tissue from autopsies of COVID-19 patients to confirm that the virus was detectable in the heart itself.

But by itself, this finding isn’t particularly informative. The heart is a complex organ that relies on a combination of muscle cells, blood vessels to supply them with nutrients and oxygen, and specialized conductive cells that help coordinate the electrical impulses that drive beating. Problems with any of these could potentially cause some of the issues seen here.

While details of what the virus might do have not yet appeared in the peer-reviewed literature, there is a draft paper that seems to fill in much of the detail. To find out which cells the virus might infect, the researchers sent stem cells to produce heart muscle cells and then exposed them to the virus. These may be infected with the virus, although it is relatively easy to infect cells in culture dishes.

Still, the researchers identified the main signs of the viral infection in these culture cells: changes in the activity of specific genes and disruption of some muscle structures. They then turned to samples of heart tissue from donors who had died from COVID-19 and used them to show that similar changes had occurred in this heart tissue. Combined, these results indicate that at least some of the problems seen in COVID-19 patients likely result from the infection of the heart muscle by the virus.

Too many unknowns

So there is certainly support for the possibility that some of the athletes mentioned in the recent news reports are seeing a direct impact of COVID-19 on heart function. But without the kind of data seen in these studies, it’s impossible at this point to establish a direct connection. The studies have identified what to look for with the help of blood tests and MRIs; whether these tests were done is not clear based on public statements.

Much follow-up work is needed to understand what goes on in the hearts of COVID-19 patients. We still don’t know when the heart symptoms appear, how long they last, or what factors make them more likely to occur. The fact that they exist at all should inform our management about the pandemic. Some proposed approaches imply that otherwise healthy, younger people are at increased risk of infection. If cardiac complications occur at the rates seen in some of these studies, that approach could pose unacceptable risks.

Updated with new information from ESPN.

By akfire1

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