Young people who develop multisystem inflammatory syndrome after being infected with the new coronavirus may experience heart-related symptoms similar to those seen with two rare, but serious, conditions called Kawasaki disease and toxic shock syndrome, the researchers said.
In some, this may include a reduced ability for the heart to pump oxygenated blood to the tissues of the body or development of a heart aneurysm.
"This is a new childhood disease that is believed to be associated with [COVID-19], and it can be lethal because it affects multiple organ systems [including] the heart and the lungs, gastrointestinal system or neurologic system," neonatologist Alvaro Moreira said in a statement.
"Children might have no symptoms, no one knew they had the disease, and a few weeks later, they may develop this exaggerated inflammation in the body," said Moreira, an assistant professor of pediatrics at The University of Texas Health Science Center at San Antonio.
Moreira and his colleagues reviewed 662 of multisystem inflammatory syndrome cases reported worldwide between Jan. 1 and July 25. Almost half of patients who had it also had an underlying medical condition. Of those, half were obese or overweight.
Seventy-one percent of the children who developed the condition after being infected with COVID-19 were admitted to intensive care units, and 60% had symptoms of shock, the data showed.
More than half -- 54% -- had abnormal findings on echocardiograms of their hearts, suggesting damage. Roughly one in five required mechanical ventilation to maintain breathing, and 11 died in the hospital, researchers said.
The damage spotted on EKGs included dilation of coronary blood vessels, a phenomenon also seen in Kawasaki disease, and depressed ejection fraction, which indicates a reduced ability for the heart to pump oxygenated blood to the rest of the body.
In addition, almost 10% of children had an aneurysm of a coronary vessel, or a ballooning of the blood vessel that can be measured on an ultrasound of the heart, which places them at high risk for future heart-health problems, Moreira said.
"These are children who are going to require significant observation and follow-up with multiple ultrasounds to see if this is going to resolve or if this is something they will have for the rest of their lives, and that's catastrophic to a parent who had a previously healthy child," he said.
Most of the 662 children suffered cardiac involvement as indicated by elevated levels of a protein that regulates muscle contraction called troponin -- up to 50 times higher than normal -- which is used with great accuracy in adults to diagnose heart attacks.
On the positive side, children who develop multisystem inflammatory syndrome seem to respond well to treatments typically used in Kawasaki disease, including imunoglobulin and glucocorticosteroids.
"Evidence suggests that [these] children ... have immense inflammation and potential tissue injury to the heart, and we will need to follow [them] closely to understand what implications they may have in the long term," Moreira said.