Al-Mallah was seeing patients in his clinic who said they were feeling normal before COVID, but after infection, they were having palpitations and shortness of breath. 

"At first, we thought this was myocarditis like with any other virus, so we did a lot of MRIs on these patients and we found they were mildly abnormal, and many others were normal. This was not myocarditis, so we asked if maybe it was with the vasculature. We knew that COVID did have some interaction on the endothelial cells, which are responsible for vasodilation," Al-Mallah explained. "Our analysis suggests that patients with prior COVID-19 infection have higher rates of reduced MFR, and that reduced MFR is a marker of a poor prognosis."

They performed PET on 271 patients with long-COVID symptoms. Each was matched with a group of 815 control subjects with similar ages and comorbidities who had normal PET scans.

"We found they were not able to dilate their arteries as much as a matched normal cohort of patients," Al-Mallah said. "This phenomena happened in the sicker patients, so if a patient was admitted to the hospital or to the ICU, then they had the higher odds of having this. We also noted this was much less prevalent with the Omicron variant, but was seen more with the Delta and Beta variants."

Patients do appear to slowly recover, based on the study. Al-Mallah said patients scanned nine months after infection had half the prevalence of microvascular dysfunction compared to patients who were more recently sick.

"This is at least giving us a hint that this is most likely starting to fade away. And clinically, I am seeing less of these patients at my clinic. Most of these symptoms appear in the first year after infection," he said.

The authors of the study noted that it is limited by its single-center design, use of chart review for follow-up and a high prevalence of cardiovascular risk factors, including obesity. But the findings are particularly relevant to long-haul COVID-19 patients, and may explain the persistence of cardiopulmonary symptoms. 

Teams from Washington University and Brigham and Women's Hospital also conducted similar PET studies and reached the same conclusions in recent months, Al-Mallah added.  

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