More Hints That Cardiac Abnormalities Resolve Fully After MIS-C

Life-threatening arrhythmias are unlikely in children who recover from multisystem inflammatory syndrome (MIS-C) following acute—sometimes asymptomatic—COVID-19, and any ventricular dysfunction and coronary abnormalities seen during hospitalization tend to resolve over time, according to a study using cardiopulmonary exercise testing (CPET) 3 to 6 months later.

Earlier reports uncovered evidence of myocarditis and arrhythmias among children who develop this rare inflammatory response to the virus. Just how much cardiac or lung capacity remains impaired over the longer-term was unclear, although other recent studies have hinted at resolution.

As such, these findings are “reassuring,” said Nicholas Robles, MD (Phoenix Children’s Hospital, AZ), first author on a research letter published today in the Journal of the American College of Cardiology.  Though the sample size is modest, “this is still the largest study describing CPET outcomes in patients following hospitalization for MIS-C. There may be rare long-term complications, but a larger study would be needed to find those.”

Robles and colleagues took a retrospective look at the patients hospitalized for MIS-C at their institution (mean age 12), who were discharged with the advice to refrain from exercise. All were referred for CPET prior to having those restrictions lifted and 48 patients, representing just over half of the cohort, came back for testing.

A mean of 5.1 months after hospitalization, heart rate and blood pressure responses during exercises tests were normal in all patients and no malignant arrhythmias were uncovered on CPET or Holter monitoring.

Exercise capacity was trickier to parse, partly because all of the patients had been counselled to avoid physical exertion over the last several months, but also possibly due to the high levels of overweight and obesity in the cohort: 56% of the hospitalized cohort had body mass index above the 85th percentile. After controlling for weight, absolute peak oxygen consumption (VO₂) was reduced in 45% of children undergoing CPET. A smaller proportion of participants had signs of ventilatory efficiency abnormalities, the etiology of which is “unclear,” the authors acknowledge.

“They’re not ventilating as efficiently as is normal,” Robles elaborated in an email. “However, I cannot say with certainty that this is a result of MIS-C. It is possible that there are some effects of COVID-19 infection that persist. We did not have an adequate population of children who underwent stress testing that had COVID-19 without MIS-C to use as a control group.”

Of note, Robles clarified that while only half of the MIS-C patients at their hospital returned for CPET, there were no differences in patient characteristics between those who returned and those who didn’t. “We feel the study population was representative of the whole population of patients hospitalized for MIS-C at Phoenix Children’s,” he said.