One of COVID-19’s mysteries is how it can cause heart attack-like symptoms in patients, leading researchers to believe the stress of the virus harms the muscle in atypical ways.

In a study recently published in the New England Journal of Medicine, a team of New York University researchers detailed how the virus triggered classic signs of a heart attack on the electrocardiograms of 18 New York City patients with severe COVID-19. None of the patients, however, had the blocked artery that typically triggers a heart attack.

Ten percent of the patients – who averaged 63 years old – showed the elevated electrocardiogram reading indicative of heart attack at hospital admission, and the other eight while hospitalized. Additional testing showed that more than half had a heart attack not caused by artery blockage. Thirteen of them died.

The research team surmised that the underlying cause for some of the deaths was the physical and emotional stress caused by COVID-19. They added that the virus might injure the heart by rupturing plaque in blood vessels, lowering the body’s oxygen level, causing coronary spasms or floating tiny, undetected clots.

The situation is challenging to treat, since the usual approach would be to administer clot-busting drugs but the patients have no major blockages.

The study underscored a separate research article in the Journal of the American Medical Society Cardiology report, which was based on statistics from China, where the COVID-19 pandemic originated.

“We’re not sure yet if it is a direct attack of the virus to the heart or if this is just a reflection of the systemic inflammation and multisystem failure,” says Dr. Heather Swales, director of the Women’s Heart Wellness Center at The Hospital of Central Connecticut in New Britain. “But, it can happen to anyone.”

About 10 percent of people with preexisting cardiovascular disease who contract COVID-19 will die. Those with high blood pressure are also at increased risk. A percentage of the New York patients studied had high blood pressure while others had such chronic conditions as diabetes and high cholesterol.

Dr. Swales said it’s still unclear if these patients are dying because of heart disease or age.

“There’s a clear issue with lack of immunity,” she said. “As we get older, all of our immune systems decrease in function.”