On Mar. 1, 2021, a study from Washington University School of Medicine in St. Louis provided evidence that COVID-19 patients’ heart damage is caused by the virus invading and replicating inside heart muscle cells, leading to cell death and interfering with heart muscle contraction.

The researchers used stem cells to engineer heart tissue that models the human infection and could help in studying the disease and developing possible therapies. The study was published in the Journal of the American College of Cardiology.

“Early on in the pandemic, we had evidence that this coronavirus can cause heart failure or cardiac injury in generally healthy people, which was alarming to the cardiology community,” said senior author Kory J. Lavine, MD, PhD, associate professor of medicine. “Even some college athletes who had been cleared to go back to competitive athletics after COVID-19 infection later showed scarring in the heart. There has been debate over whether this is due to direct infection of the heart or due to a systemic inflammatory response that occurs because of the lung infection.

“Our study is unique because it definitively shows that, in patients with COVID-19 who developed heart failure, the virus infects the heart, specifically heart muscle cells.” They also showed that this cell death and loss of heart muscle fibers can happen even in the absence of inflammation. “Inflammation can be a second hit on top of damage caused by the virus, but the inflammation itself is not the initial cause of the heart injury,” Lavine said.

Part of the reason these questions of causation in heart damage have been hard to answer is the difficulty in studying heart tissue from COVID-19 patients. The researchers were able to validate their findings by studying tissue from four COVID-19 patients who had heart injury associated with the infection, but more research is needed.