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A minority of people recovering from COVID-19 underwent a brief period of localized myocardial inflammation accompanied by cardiac injury and higher levels of systemic inflammatory blood markers, researchers found.

Myocardial inflammation, flagged as focal fluorodeoxyglucose (FDG) uptake on combined PET/MRI scans, was visible in eight out of 47 people more than 2 months after COVID-19 diagnosis, according to investigators led by Kate Hanneman, MD, MPH, of University of Toronto and the Toronto General Hospital.

These PET-positive patients tended to have more abnormalities on cardiac MRI compared with the other COVID survivors from the same center:

• Higher regional T2, T1, and extracellular volumes

• Greater prevalence of late gadolinium enhancement

• Lower left ventricular ejection fraction

• Worse global longitudinal and circumferential strain

Moreover, the group with myocardial inflammation also had higher blood levels of interleukin-6, interleukin-8, and high-sensitivity C-reactive protein, Hanneman's group reported online in

The good news was that inflammation and cardiac function generally resolved or improved according to follow-up tests performed on average 52 days after the initial finding of myocardial inflammation on PET.

"Overall, the study findings suggest an imaging phenotype that is expected to have good prognosis. However, longer-term follow-up studies are required to understand the need for ongoing cardiac surveillance, relationship to cardiac symptoms, guidance for safe return to exercise and sports participation, and long-term cardiovascular disease risk," the study authors concluded.

Notably, two out of eight people had focal FDG uptake without any cardiac MRI abnormalities. "This suggests that inflammation may be the only manifestation in a small proportion of patients and highlights the incremental value of combined FDG-PET/MRI compared with MRI alone," Hanneman and colleagues said.

They also reported that both groups shared normal high-sensitivity troponin I levels at the time of PET/MRI.

"This suggests that there was no ongoing myocyte necrosis at the time of imaging and that troponin is a poor screening test for ongoing inflammation ... It is possible that a more intense systemic inflammatory process may be contributing to cardiac inflammation and the consequential alteration to regional and global myocardial function in PET-positive participants," the researchers suggested.

Their prospective cohort study included 47 adults (mean age 43 years, split between the sexes) who had been recruited within 3 months of COVID-19 diagnosis at a single center and evaluated from November 2020 to June 2021.

Home recovery from COVID-19 was sufficient for 85% of participants, whereas 9% were admitted to the wards and 6% were sent to the ICU.

Patients spent on average 67 days between COVID-19 diagnosis and PET/MRI. At the time of PET/MRI, 40% reported at least one cardiac symptom. Over a quarter of patients had received at least one dose of a COVID-19 vaccine prior to their scans.

PET and MRI images were fused by translating and rotating PET images onto the MRI coordinate system. Scans were analyzed by three experienced imagers. All patients with focal FDG uptake at baseline returned for repeated tests at 2 months.

The study was limited by the small sample and potential for survivor and selection biases, Hanneman's group acknowledged.

"These findings should be confirmed in future multicenter studies, ideally with comparison with age-, sex-, and comorbidity-matched controls," the authors said.

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