Microthrombi, necrosis seen in COVID-19 hearts on autopsy
Autopsies on patients who died from COVID-19 are providing important clues on how to treat the disease. In an analysis of 40 hearts from COVID-19 patients who died early in the pandemic, myocyte necrosis was seen in 14 hearts, or 35%.
In the majority of these hearts, pathologists found both small areas of focal necrosis and cardiac thrombi, most of which were microthrombi in myocardial capillaries, arterioles, and small muscular cells.
In an interview, senior author Aloke V. Finn, MD, CVPath Institute, Gaithersburg, Md., stressed the importance of understanding what they saw, but also what they didn’t see.
“What we saw in the majority of patients with myocardial injury were these small areas of infarct and microthrombi in small vessels. What we didn’t see was any evidence of myocarditis and or huge infarcts in, like, the LAD artery,” he said.
“What we’re seeing here is not clinically detectable. … There is no test that will tell you there are microthrombi and no imaging tests that will show these focal areas of necrosis, but that doesn’t mean it’s not there,” he added.
The finding of myocyte necrosis in about one-third of samples is consistent with another study that showed that 30%-40% of patients hospitalized with COVID-19 have elevated troponins, noted Dr. Finn. The investigators were unable to obtain troponin levels on their patients, which could limit the clinical translation of myocardial necrosis detected at autopsy.
Dr. Finn and colleagues, including first author Dario Pellegrini, MD, from Ospedale Papa Giovanni XXIII in Bergamo, Italy, published their findings online in Circulation on Jan. 22, 2020.
The report is a follow-up to another just published by Dr. Finn’s group in the Journal of the American College of Cardiology, which showed that myocarditis is a very rare finding in COVID-19 autopsies.
Only three of 14 individuals (21.4%) with evidence of myocyte necrosis showed evidence of acute MI, which Dr. Finn and colleagues define as an area of necrosis at least 1 cm2 in size. The remaining 11 (78.6%) had only discrete areas of myocyte necrosis (>20 necrotic myocytes with an area of ≥0.05 mm2, but <1 cm2).
“This makes sense when we saw what type of thrombus there was in these cases; it wasn’t thrombus in major epicardial vessels but microthombi in small vessels,” said Dr. Finn.
In those with necrosis, cardiac thrombi were present in 11 of 14 (78.6%) cases, with 2 of 14 (14.2%) having epicardial coronary artery thrombi and 0 of 14 (64.3%) having microthrombi in myocardial capillaries, arterioles, and small muscular arteries.
Further supporting the role of COVID-19–related hypercoagulability as the cause of myocardial injury in many patients, the investigators noted that the incidence of severe coronary artery disease (defined as >75% cross sectional narrowing) did not differ significantly between those with and without necrosis.
COVID-19 vs. non–COVID-19 thrombi
Going one step further, Dr. Finn’s team compared cardiac microthrombi from their COVID-19–positive autopsy cases with intramyocardial thromboemboli from COVID-19 cases. They also compared the samples with aspirated thrombi obtained during primary percutaneous coronary intervention from uninfected and COVID-19–infected patients presenting with ST-segment elevation MI (STEMI).
The autopsy-obtained microthrombi had significantly more fibrin and terminal complement C5b-9 immunostaining than intramyocardial thromboemboli from COVID-19–negative subjects and than aspirated thrombi from either COVID-positive or COVID-negative STEMI patients.
“Basically, what we’re seeing in these thrombi is evidence of an immune-mediated reaction,” said Dr. Finn, explaining that complement C5b-9 is an innate immune system protein that circulates in the blood in response to any kind of activation of the immune system. “It is nonspecific but can also lead to coagulation problems,” he said.
