Heart injuries caused by COVID-19 do not appear to worsen after patients leave hospital, research published this week has suggested.
The peer reviewed study, conducted by a team from Monash University's Baker Heart and Diabetes Institute and University College London, looked at hospitalised non-vaccinated COVID-19 patients.
A total 235 patients were surveyed both during their initial hospitalisation and six months after being released.
It found that while after six months some scarring on the heart remained unchanged, inflammation and overall quality of life appeared to improve.
"In general, the findings are reassuring," the report said.
"Even in this non-vaccinated population with severe COVID-19 and evidence of a myocardial injury, major long-term cardiac sequelae [after-effects] were uncommon, and health status improved in most patients.
"[No participant] showed evidence of new micro-infarcations [blood supply obstructions].
"This suggests that further thromboembolic [blood clotting] events related to COVID-19 do not occur after the initial infection has resolved.
"The near-universal resolution of the [health conditions] observed …. Also indicates that the inflammatory effects of COVID-19 on the pericardium, pleura, and lungs are also generally short-lived and non-progressive."
The report was published in scientific journal JACC: Cardiovascular Imaging on Thursday.
It was published alongside commentary by Ohio State University's director of Cardiac Imaging, Dr Yuchi Han, and University of Pennsylvania cardiologist Dr Mahesh Vidula.
"The study provides optimistic data for this high-risk population showing that over a follow-up period of six months, ventricular scarring did not worsen, myocardial scar did not progress," they wrote.
"There was no sub-acute deterioration of cardiac function … and adverse events were low at 12 months.
"However, there are important issues that deserve further investigation and caution against underestimating the potential long-term risk for … adverse events in this high-risk group."
Limitations noted by both doctors and the research team include the lack of longer term follow up and that more patients initially tested did not return at the six month mark.
"Almost one in three patients did not re-attend for the follow-up visit, raising the potential for survivor/disease severity bias," the report said.
"The missing data may have led to biased estimates of the observed improvements in quality of life and physical functioning."
Professor Jason Kovacic is the director and chief executive of the Victor Chang Cardiac Research Institute, a Professor of Medicine at the University of NSW and an adjunct professor at the University of Western Australia.
He told the ABC the study was reassuring but noted long-term follow up was still important.
"These were high-risk people, they also had significant comorbidities in terms of diabetes, high blood pressure and those sorts of things," he said.
"So being sure that longer term follow up over several years continues to show good cardiac outcomes is important.
"Performing similar studies in patients that do have long COVID … is also an important area of research.
"This study was done in the pre-vaccination era, it was early on in the COVID experience when perhaps subjectively the virus was more aggressive, it was causing more harm.
"In the current era the infections we're seeing tend to be far more mild, so that's also reassuring.
"But for people who are contracting COVID now, the data in this study isn't as relevant because the virus isn't as aggressive as it was back in that era."
Dr Isuru Ranasinghe, a senior cardiologist at The Prince Charles Hospital and an Associate Professor in Cardiology with the University of Queensland, said the findings were consistent with what clinicians were seeing.
"Myocarditis … usually we can do a blood test to detect it," he said.
"Many, many viruses can cause [this condition]. It happens because the body's antibodies that typically attack the virus also [attack] the heart muscle and the immune system while fighting the virus.
"What this study did was actually document the inflammation with a scan that shows the swelling very well and it's the best test for myocarditis.
"Then they followed it up … and what they found was there's very little progression in the majority of patients.
"That's very reassuring. If there's a population to keep in mind, it's people who had not had mild COVID [or] had it at home [but] patients who needed admission to hospital.
"This is a sicker group of people."
Dr Ranasinghe noted similar research carried out on Australian patients across 21 different hospitals, testing for cardiac complications.
The study published in September 2021 found there was a low incidence of clinical heart complications when admitted to hospital with COVID-19.
Complications were found to be "especially uncommon" in those under the age of 65.