key: cord-1050017-whhuzz12
authors: Kawakami, Rika; Sakamoto, Atsushi; Kawai, Kenji; Gianatti, Andrea; Pellegrini, Dario; Nasr, Ahmed; Kutys, Bob; Guo, Liang; Cornelissen, Anne; Mori, Masayuki; Sato, Yu; Pescetelli, Irene; Brivio, Matteo; Romero, Maria; Guagliumi, Giulio; Virmani, Renu; Finn, Aloke V.
title: Pathological Evidence for SARS-CoV-2 as a Cause of Myocarditis: JACC Review Topic of the Week
date: 2021-01-26
journal: J Am Coll Cardiol
DOI: 10.1016/j.jacc.2020.11.031
sha: 6bc69136b1df20262350025e84b59f6fd60bb07d
doc_id: 1050017
cord_uid: whhuzz12

To investigate whether severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2)–induced myocarditis constitutes an important mechanism of cardiac injury, a review was conducted of the published data and the authors’ experience was added from autopsy examination of 16 patients dying of SARS-CoV-2 infection. Myocarditis is an uncommon pathologic diagnosis occurring in 4.5% of highly selected cases undergoing autopsy or endomyocardial biopsy. Although polymerase chain reaction–detectable virus could be found in the lungs of most coronavirus disease-2019 (COVID-19)–infected subjects in our own autopsy registry, in only 2 cases was the virus detected in the heart. It should be appreciated that myocardial inflammation alone by macrophages and T cells can be seen in noninfectious deaths and COVID-19 cases, but the extent of each is different, and in neither case do such findings represent clinically relevant myocarditis. Given its extremely low frequency and unclear therapeutic implications, the authors do not advocate use of endomyocardial biopsy to diagnose myocarditis in the setting of COVID-19.

subjects in our own autopsy registry, in only 2 cases was the virus detected in the heart. It should be appreciated that myocardial inflammation alone by macrophages and T cells can be seen in noninfectious deaths and COVID- 19 Another potential mechanism of cardiac injury that has been proposed is direct entry of the virus into endothelial cells in the heart without necessarily entering myocytes. Direct endothelial infection has been documented in autopsy hearts as well as in glomerular endothelial cells using electronic microscopy with identification of virus particles, although in some cases their appearance and location within cells was not typical of coronavirus infected cells (7) (8) (9) . We believe other techniques such as in situ hybridization should be used to confirm such findings. In our own experience using both techniques, we have not been able to document a single case of endothelial infection by SARS-CoV-2 in the heart. From these data, it seems difficult to conclude that endothelial tropism is a major mechanism of COVID-19induced cardiac injury without more confirmation.

Another, and perhaps better supported, idea is that cardiac injury can be induced via hyperactivation of the immune system characterized by the release of multiple inflammatory mediators, including interleukins, tumor necrosis factors, and so on. Circulating levels of these factors that exceed normal thresholds can result in collateral damage.

The term cytokine storm has been used to describe this condition, which has been reported in severely ill COVID-19 patients (10) . Microvascular and macrovascular thrombi that result from the activation of platelets, neutrophils, and other proteins may contribute to vascular occlusion and cell death (11) .

We recently reported a case of myocardial infarction and cardiogenic shock caused by cardiac microvascular thrombosis in a young woman with COVID-19 (12) . In this case, the virus was not detectable by polymerase chain reaction (PCR) in the heart. However, the exact pathogenesis of cardiac injury induced by COVID-19 infection remains to be elucidated, but we believe the most compelling evidence points toward cytokine-storm-related effects.

Despite having endured the COVID-19 pandemic for over 6 months, many questions still remain about the best approaches for determining causes of cardiac injury in both hospitalized and nonhospitalized patients. In most cases, cardiac injury appears to result within the context of the overall respiratory infection rather than the first manifestation of disease. Coagulation abnormalities that may result as a part of the immune response to the disease have been shown to predispose these patients toward thrombotic processes, both in the venous and arterial circulation (11) . 

Whether myocarditis is a cause of myocardial injury in patients with COVID-19 is uncertain.

Myocarditis is uncommon in autopsy or EMB in cases of COVID-19.

Further work is needed to fully understand the cardiac effects of COVID-19 infection. *"Borderline myocarditis" cases counted as not diagnostic of myocarditis. †Very low level of virus was detected by PCR (likely contamination by circulating virus rather than direct infection). ‡5 patients had virus detected in other tissues although not clearly stated which tissues virus was detected in. §12 patients showed new ECG abnormality including atrial fibrillation, premature ventricular beats, bundle branch block, and ST-segment abnormality. Only 5 cases were evaluated by cardiac ultrasound without any evidence of impaired cardiac function. kThe same case series was reported in other papers (PMID 32689809, 32473124). ¶Virus load was lower than 1,000 copies in 8 patients and was above 1,000 copies in 16 patients.

Aut ¼ autopsy; CAD ¼ coronary artery disease; CHF ¼ chronic heart failure; CKD ¼ chronic kidney disease; COVID-19 ¼ coronavirus disease-2019; DCM ¼ dilated cardiomyopathy; DM ¼ diabetes mellitus; EF ¼ ejection fraction; EM ¼ electron microscopy; EMB ¼ endomyocardial biopsy; HCM ¼ hypertrophic cardiomyopathy; HD ¼ heart disease; HF subjects with clinically suspected myocarditis whose nasopharyngeal swab tests for COVID-19 were negative but the virus was recovered by PCR from EMB In addition to the possibility of false-negative PCR results during tissue sampling, it is also likely that given the low overall expression of ACE2 receptor in myocardial cells, tropism of SARS CoV-2 for the heart is not likely (32) . Takotsubo syndrome is another potential cause of myocardial injury in the setting of electrocardiographic abnormalities and troponinpositive results with normal coronaries and should also be considered. In such cases, patients are known to have regional wall motion abnormalities, injury to myocytes, and infiltration of lymphocytes and macrophages in autopsy specimens. However, to be sure of the diagnosis, this requires exclusion of myocarditis. Troponin levels and CMR signs of edema can be found in both entities and each can mimic the other.

In a series of 384 autopsy cases (239 cardiac, 51 noncardiac, and 94 non-natural deaths), inflammatory infiltrates were found in the heart in 18% of all cases, with multifocal infiltrates in 9%. Incidental infiltrates were most frequent in natural noncardiac deaths (31%), but were also seen in drug-related deaths (20%) and cardiac deaths (16%), and were least frequent in traumatic deaths (16%) (21) . We previously reported autopsy findings in the hearts of patients dying during viral infection (in this case during the AIDS epidemic) and showed that focal mild inflammatory infiltrates not meeting the definition of myocarditis in the heart were not uncommon (31%) (20) . We also found focal mild mononuclear inflammatory infiltrates in 10 of 24 (42%) hearts in sudden traumatic deaths. Because these foci were not associated with myocyte necrosis, they were not diagnosed as myocarditis.

We Continuous values are expressed by a median (interquartile range). *Degree of inflammation in epicardium was classified into 3: mild ($50 and <100 per mm 2 ), moderate ($100 and <500 per mm 2 ), and severe ($500 per mm 2 ). †Additional examination by immunohistochemistry was done (see Figure 1 ). ‡Neutrophil infiltration in the area of acute myocardial infarction.

AH ¼ alveolar hemorrhage; AMI ¼ acute myocardial infarction; BP ¼ bronchial pneumonia; DAD ¼ diffuse alveolar damage due to coronavirus; LA ¼ left atrium; Lym ¼ lymphocytes; ND ¼ not detected; Neut ¼ neutrophils; Plasma ¼ plasma cells; PT ¼ pulmonary thrombus; RA ¼ right atrium; y/n ¼ yes or no; other abbreviations as in Table 2 .

to the clinical details. All tissue specimens were fixed in 10% buffered formalin for at least 72 to 96 h prior to shipment. Whole hearts and lungs (either paraffin blocks or tissues), were sent to CVPath Institute for pathological examination. Table 2 , the average age of the subjects was 70 years, and 69% were men. In total, 4 subjects Table 3) .

We also evaluated the nature of the inflammatory cells found in the myocardium in cases of (noninfectious) traumatic (control) versus COVID-19 deaths. We examined histological sections from the left ventricles from 5 randomly selected cases of control death from our CVPath registry and from 5 randomly selected cases of subjects dying of COVID- Table 2 for list of cases selected). We stained left ventricular myocardial sections using antibodies against CD3 (T-cell marker) and CD68 (macrophage).

Overall, there was no difference in the total number of T cells and macrophages in the 2 groups ( Figure 1) . However, the cell counts in COVID-19 hearts were higher than what others have used to diagnose myocarditis. We believe because these cells are scattered and not accompanied by myocyte necrosis, these cases do not fulfill the criteria of myocarditis. Moreover, CD3 cells were significantly more frequent in control cases than in COVID-19 cases, whereas macrophages were more frequent in COVID-19 than in control cases, but we did not determine their exact location (i.e., interstitium vs. intravascular). Figure 1 contrasts these results with a typical case of mild myocarditis from the CVPath biobank, which showed greater CD3 abundance than infection. 

Spectranetics, Surmodics, Symic, Vesper, W.L. Gore, and Xeltis. Dr. Cornelissen has received research grants from University Hospital RWTH

Terumo Corporation, W. L. Gore, and Spectranetics; and has served as a consultant for Abbott Vascular

ADDRESS FOR CORRESPONDENCE: Dr. Aloke V

Firstfield Road, Gaithersburg, Maryland 20878, USA. E-mail: afinn@ cvpath.org. Twitter: @alokefinn, @CVPath_MD

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