COVID-19–Associated Nonocclusive Fibrin Microthrombi in the Heart

Abstract

Background: Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and its resultant clinical presentation, COVID-19, is an emergent cause of mortality worldwide. Cardiac complications secondary to this infection are common; however, the underlying mechanisms of such remain unclear. A detailed cardiac evaluation of a series of COVID-19 individuals undergoing postmortem evaluation is provided, with four aims: 1) describe the pathologic spectrum of the myocardium; 2) compare to an alternate viral illness; 3) investigate angiotensin converting enzyme 2 (ACE2) expression; and 4) provide the first description of the cardiac findings in patients with cleared infection. Methods: Study cases were identified from institutional files and included COVID-19 (n=15; 12 active, 3 cleared), influenza A/B (n=6), and non-virally mediated deaths (n=6). Salient information was abstracted from the medical record. Light microscopic findings were recorded. An ACE2 immunohistochemical H-score was compared across cases. Viral detection encompassed SARS-CoV-2 immunohistochemistry, ultrastructural examination, and droplet digital polymerase chain reaction (ddPCR). Results: Male sex was more common in the COVID-19 group (p=0.05). Non-occlusive fibrin microthrombi (without ischemic injury) were identified in 16 cases (12 COVID-19, 2 influenza, and 2 controls), and were more common in the active COVID-19 cohort (p=0.006). Four active COVID-19 cases showed focal myocarditis, while one case of cleared COVID-19 showed extensive disease. Arteriolar ACE2 endothelial expression was lower in COVID-19 cases versus controls (p=0.004). ACE2 myocardial expression did not differ by disease category, sex, age or number of patient comorbidities (p=0.69, p=1.00, p=0.46, p=0.65, respectively). SARS-CoV-2 immunohistochemistry showed non-specific staining, while ultrastructural examination and ddPCR were negative for viral presence. Four (26.7%) COVID-19 patients had underlying cardiac amyloidosis. Cases with cleared infection had variable presentations. Conclusions: This detailed histopathologic, immunohistochemical, ultrastructural and molecular cardiac series showed no definitive evidence of direct myocardial infection. COVID-19 cases frequently have cardiac fibrin microthrombi, without universal acute ischemic injury. Moreover, myocarditis is present in 33.3% of active and cleared COVID-19 patients, but is usually limited in extent. Histologic features of resolved infection are variable. Cardiac amyloidosis may be an additional risk factor for severe disease.

Comparison of In Situ Hybridization, Immunohistochemistry, and Reverse Transcription–Droplet Digital Polymerase Chain Reaction for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Testing in Tissue

“…In addition to lung specimens, 1 umbilical cord (other institution), 22 hearts (12 autopsy heart specimens from our institution one of which has been previously reported 21…”

“…28 The significance of the low copy numbers by ddPCR in the autopsy hearts from ProteoGenex in our study is not entirely clear, especially in light of multiple prior reports including one from our institution not revealing any virus in hearts from COVID-19 patients. 18,21,24 Low level contamination might be a possibility as all these FFPE tissue blocks were derived from a single company. On the other hand, these results might represent true low levels of SARS-CoV-2 in these hearts.…”

“…Recently, ddPCR has been shown to have a significantly lower limit of detection of SARS-CoV-2 in nasopharyngeal swabs than RT-PCR. 20 While we recently showed that ddPCR did not detect SARS-CoV-2 infection in heart tissue from COVID-19 patients 21 , this technique has not been thoroughly validated in FFPE specimens of other organs, specifically the lung, and has not been compared to other techniques in its capability to identify the virus in FFPE tissue.…”

COVID-19 letter to the editor: Epicardial fat inflammation as possible enhancer in COVID-19?

“…This reduction in ACE2 was associated with EAT inflammation, partly due to the virus taking advantage of more ACE2-binding sites for internalization of the virus into adipocytes and then triggering an augmented inflammatory signaling cascade. Bois et al also showed that a high proportion of COVID-19 deaths were accompanied with cardiac amyloidosis [6], which may be an additional risk factor for severe clinical condition. It is of great significance to find out a specific biomarker to predict adverse outcomes in patients with COVID-19.…”

“…Based on experimental evidence, ACE2 and inflammatory cytokines, tumor necrosis factor-α and interleukin-6, were demonstrated to be expressed at higher levels in EAT in heart explants removed from obese patients [5]. In addition, Bois et al reported lower ACE2 endothelial expression in COVID-19 cases versus influenza A/B or non-virally mediated deaths [6]. This reduction in ACE2 was associated with EAT inflammation, partly due to the virus taking advantage of more ACE2-binding sites for internalization of the virus into adipocytes and then triggering an augmented inflammatory signaling cascade.…”