Small, dark purple spots show inflammatory cells penetrating the heart of a patient who died of COVID-19.
James Stone
By Emma Yasinski
ScienceThe COVID-19 reporting is supported by the Heising-Simons Foundation.
Three-quarters of the people who died from COVID-19 carried the SARS-CoV-2 virus in their hearts, according to the detailed study of heart tissue so far. These people were also more likely to experience abnormal heart rhythms before they died than patients without heart attack. The study provides insight into how the disease can damage the heart – and how certain treatments can help.
The finding ‘paints a pretty good picture’ of the link between the virus and heart problems, says Joseph Maleszewski, a cardiovascular pathologist at the Mayo Clinic who was not involved in the study.
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Scientists have ample evidence of heart damage in COVID-19 patients. For example, some people show elevated levels of troponins, molecules that are released into the bloodstream when the heart is injured. Others have experienced inflammation of the sac that surrounds the heart – and inflammation of the heart itself. But it is unclear whether these problems were caused by the SARS-CoV-2 virus that directly attacks the heart, or that the damage is due to an overactive immune response.
Part of the problem is that previous studies have mixed on whether SARS-CoV-2 can invade heart tissue. Lots of it do not have found that the virus uses real-time polymerase chain reaction (RT-PCR), says James Stone, a cardiovascular pathologist at Massachusetts General Hospital. RT-PCR works by detecting viral RNA in tissue and then making many DNA copies of it. Once there is enough DNA, a molecule called a fluorescent label can attach to it and shine to reveal its presence. But Stone says that heart tissue is often processed and preserved using chemicals such as paraffin, which can break down RNA and prevent detection.
So he and his team used a different approach: in situ hybridization and NanoString transcriptomic profiling. Like RT-PCR, these techniques use special molecules to attach and detect pieces of viral RNA, but this is done without first making DNA copies. The approach can identify viral RNA even after it has been broken down into smaller pieces. The scientists also analyzed about 1,000 pieces of heart tissue – more than 20 samples from each of the 41 patients they looked at. That’s double the number of samples per patient in most studies, Stone says.
SARS-CoV-2 was present in 30 hearts, the team reported today Modern pathology. And only the patients experienced new atrial fibrillation, rapid and irregular heart rhythms or early or extra heartbeat, compared to the other patients in the study – a correlation that Stone calls ‘fairly phenomenal’.
However, it is unclear whether the virus directly attacked the heart in these cases. Most infected heart cells were immune cells, which could have penetrated SARS-CoV-2 elsewhere in the body before traveling to the heart. It is also unclear whether the virus causes the problems rather than the immune cells themselves.
Regardless, the study may help explain why the steroid dexamethasone is so helpful for some patients. The drug was one of the first to be found to prevent deaths due to severe COVID-19. It reduces inflammation, so it can limit the presence of SARS-CoV-2, which contains immune cells in the heart, Stone says. Only 50% of the patients treated with dexamethasone had the virus in their hearts, compared to 90% of the patients who did not use the drug.
But compared to large clinical trials, the number of patients in this new study is small, making it impossible to say that one drug protects the heart better than another, says Nicholas Hendren, a cardiology fellow at the University of Texas.
Yet Maleszewski says the new findings are a call to action. Scientists need to examine more heart tissue, he argues, not just to see how COVID-19 kills patients, but to find out how it hurts the hearts of those who survive. The disease can, for example, create scar tissue that can cause heart problems. We are beginning to understand what COVID-19 does to patients when they have it, he says. “What is not clear is what happens later.”