key: cord-0942205-i33kgmpw
authors: Mehta, R.; Bello-Chavolla, O. Y.; Mancillas-Adame, L.; Rodriguez-Flores, M.; Ramirez-Pedraza, N.; Rodriguez-Encinas, B.; Perez-Carrion, C. I.; Jasso-Avila, M. I.; Valladares-Garcia, J.; Vanegas-Cedillo, P. E.; Hernandez-Juarez, D.; Vargas-Vazquez, A.; Antonio-Villa, N. E.; Chapa-Ibarguengoitia, M.; Almeda-Vald es, P.; Elias-Lopez, D.; Galindo-Fraga, A.; Gulias-Herrero, A.; Ponce de Leon, A.; Sifuentes-Osornio, J.; Aguilar-Salinas, C. A.
title: Epicardial adipose tissue thickness is associated with increased severity and mortality related to SARS-CoV-2 infection
date: 2021-03-24
journal: nan
DOI: 10.1101/2021.03.14.21253532
sha: fc63d82eaa22c43cd99c8b51bbe8503da6c47d25
doc_id: 942205
cord_uid: i33kgmpw

BACKGROUND: Obesity, in particular, visceral adipose tissue has been linked to adverse COVID-19 outcomes. The amount of epicardial adipose tissue (EAT) may have relevant implications given its proximity to the heart and lungs. Here, we explored the role of EAT in increasing the risk for COVID-19 adverse outcomes. METHODS: We included 748 patients with COVID-19 attending a reference centre in Mexico City. EAT thickness, sub-thoracic and pericardial fat were measured using thoracic CT scans. We explored the association of each thoracic adipose tissue compartment with critical COVID-19 and mortality according to the presence or absence of obesity. Mediation analyses evaluated the role of EAT in facilitating the effect of age, body mass index and cardiac troponin levels with adverse COVID-19 outcomes. RESULTS: EAT thickness was associated with increased risk of COVID-19 mortality (HR 1.18, 95%CI 1.01-1.39) independent of age, gender, comorbid conditions and BMI. Increased EAT was associated with lower SpO2 and PaFi index and higher levels of cardiac troponins, D-dimer, C-reactive protein, and 4C severity score, independent of obesity. EAT mediated 13.1% (95%CI 3.67-28.0%) and 5.1% (95%CI 0.19-14.0%) of the effect of age and 19.4% (95%CI 4.67-63.0%) and 12.8% (95%CI 0.03-46.0%) of the effect of BMI on requirement for intubation and mortality, respectively. EAT also mediated the effect of increased cardiac troponins on myocardial infarction during COVID-19. CONCLUSION: EAT is an independent risk factor for severe COVID-19 and mortality independent of obesity. EAT partly mediates the effect of age and BMI and increased cardiac troponins on adverse COVID-19 outcomes.

Obesity is a major risk factor for disease severity related to severe acute coronavirus 2 (SARS-CoV-2) infection 1 . Patients with obesity have a higher risk for, hospitalization, intensive care unit (ICU) admission, invasive mechanical ventilation (IMV) and death 1, 2 .

Obesity is associated with a state of low-grade inflammation, which in the setting of coronavirus disease can result in further inflammation, endothelial dysfunction and subsequent cytokine storm, increasing the risk for severe disease [2] [3] [4] . In Mexico, obesity is highly prevalent; in particular, the accumulation of abdominal visceral adipose tissue (VAT) has been shown to influence COVID-19 outcomes, independent of additional comorbid conditions and risk factors. [5] [6] [7] [8] Visceral obesity is associated with increased cardiometabolic burden, including risk of arterial hypertension, type 2 diabetes mellitus and cardiovascular disease 5 . Accumulation of VAT results in adipose tissue dysfunction, morphological changes in adipocytes, fibrosis, altered secretion of adipokines and increased inflammation 6 . VAT has proven to be related to increased risk for severe COVID-19 and need for intensive care. 11, 12 The engagement of SARS-CoV-2 with angiotensin converting enzyme 2 (ACE 2) in visceral fat is thought to impair the function of this enzyme, resulting in increased production of angiotensin II, thus enhancing the production of inflammatory cytokines. 11 Levels of ACE 2 mRNA in visceral fat correlate with body mass index; this is not the case for subcutaneous fat. Epicardial adipose tissue (EAT) is an ectopic fat deposit, located between the heart and the pericardium and is thought to contribute to adverse cardiovascular outcomes 7 .

EAT may play a significant role in mediating the effects of obesity on COVID-19 outcomes due to its thoracic localization and may influence the cardiovascular complications of COVID-19 [8] [9] [10] . In this study, we examined the association of EAT with adverse COVID-19 outcomes and explored potential pathways which may link the accumulation of EAT was mediators of well-established risk factors related to severe COVID-19.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint

This study included consecutive patients evaluated at the Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán (INCMNSZ), a COVID-19 reference centre in Mexico City between 17th March and 31st May 2020. Subjects were initially assessed at triage and required either ambulatory or in-hospital care for COVID-19, confirmed with computerized tomography (CT) and/or via RT-qPCR test from nasopharyngeal swabs. All patients had moderate to severe disease as defined by National Institute of Health criteria.

Moderate illness was defined as evidence of lower respiratory disease during clinical assessment or imaging and who have saturation of oxygen (SpO 2 ) ≥ 94% on air, and severe illness as SpO 2 <94% on air, a ratio of arterial partial pressure of oxygen to fraction of inspired oxygen (PaO 2 /FiO 2 ) <300 mm Hg, respiratory frequency >30 breaths/min, or lung infiltrates >50%). All patients underwent a chest CT, and a radiologist determined the degree of pulmonary parenchymal disease and assessed epicardial fat thickness. In addition, a medical history, anthropometric measurements and laboratory tests were obtained. The electronic files of each patient were retrospectively reviewed to document the outcomes during hospitalization. All proceedings were approved by the research and ethics committee of the INCMNZ (Ref. 3383) and informed consent was waived due to the nature of the study.

Clinical variables and laboratory measures were obtained at the time of initial evaluation.

Physical examination included: weight, height, body mass index (BMI, calculated as weight in kilograms divided by squared height in meters), pulse oximeter saturation (SpO2), respiratory rate (RR), temperature and arterial blood pressure (BP). Laboratory measurements included: full blood count, chemistry panel including liver function tests, Creactive protein (CRP), fibrinogen, D-dimer, ferritin, troponin I (TPNI), erythrocyte . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint sedimentation rate (ESR) and procalcitonin levels. The blood samples were processed at the central laboratory of the INCMNSZ.

All patients underwent unenhanced CT scans including low-dose CT and two ultra-lowdose CT protocols and commonly reported imaging features of COVID-19 pneumonia were captured. Thorax CT was performed using a 64-slice scanner (GE MEDICAL SYSTEMS Revolution EVO). Epicardial adipose tissue (EAT), the adipose tissue located between the visceral layer of the pericardium and the surface of the heart was measured.

EAT thickness was measured at 3 points (right atrioventricular fossa, left atrioventricular fossa, and anterior interventricular fossa) in the reformatted 4-chamber view using the multiplanar reconstruction (MPR) tool on the workstation (19, 20, 21) . The maximum thickness of the EAT was recorded, from the surface of the myocardium to the pericardium (measured perpendicular to the pericardium). The measurements were made on 2 different occasions, obtaining a total of 6 measurements; the average of them was used in the statistical analysis.

Pericardial adipose tissue (PAT) was quantified with the volume measurement tool with the Carestream system of the workstation. The thickness of the thoracic subcutaneous adipose tissue (TscAT) was measured from the anterior border of the sternum to the skin, at the level of the mitral valve in the axial plane of the tomography. The 80 th genderspecific percentile of EAT thickness was obtained and used as the threshold to define increased EAT thickness.

In addition, chest CT findings were recorded and used to evaluate severity of COVID infection.

Outcomes included mortality and requirement for mechanical intubation. Furthermore, a composite of death and requirement for invasive mechanical ventilation was used as a . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review)

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint definition for critical COVID-19. For time-to-event analyses, time from self-reported symptom onset prior to evaluation until last follow-up (censoring) or death, whichever occurred first was estimated. The COVID-19 specific 4C mortality score was estimated; this reflects increased risk of mortality in this population 11 .

The clinical characteristics of subjects with visceral obesity (EAT > 80 th percentile) were compared according to presence or absence of obesity, as assessed by BMI, using Student's t-test or Mann-Whitney U according to variable distribution for continuous variables and using chi-squared tests for categorical variables. To ensure variable symmetry prior to modeling, the bestNormalize R package was used and identified the better transformation as out-of-sample normalization via 10-fold cross-validation with 5 repeats for all CT-derived measurements. All statistical analyses were conducted using R 4.0.2.

The CT-derived adipose tissue measures and body-mass index (BMI) were compared between cases who eventually required mechanical ventilation or died during hospitalization and those who did not, using Student's t-test. Linear regression analysis was used to assess which clinical features were independently associated with EAT thickness in COVID-19 patients. To assess the predictive ability of each thoracic adipose tissue segment, Cox proportional risk regression models were generated including an unadjusted model (Model 1) and models adjusted for age, gender and number of comorbid conditions (Model 2) and further adjustments by BMI to assess independent risk after adjustment (Model 3). In addition, the construct of increased EAT using the definition of >80 th gender-specific percentile of EAT thickness was assessed using the same models.

To assess the impact of thoracic adipose tissue compartments on the risk of mechanical ventilation, similar models were adjusted using fixed effects logistic regression models. To . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint assess the independent effect of BMI, Models 1 and 2 were fitted for normalized BMI values for both outcomes.

The 1-unit incremental risk associated with normalized EAT measures was evaluated using Cox regression models adjusted for age, gender, number of comorbid conditions and BMI-This was further stratified by BMI-determined obesity status to evaluate the independent effect of EAT thickness in predicting mortality risk related to COVID-19 using the simPH and survival R packages.

The first hypothesis was that EAT was partially mediating the mortality risk related to age, given the association of increases in visceral and epicardial adipose tissue with aging, and BMI 12 . The secondary hypothesis was that EAT may induce cardiac damage and that this could increase COVID-19 severity and mortality risk 8 . To test these hypotheses, casual mediation analyses were conducted using the mediation R package, adjusting logistic regression models by age, gender, number of comorbid conditions or BMI as required. Confidence intervals were estimated using White's heteroskedasticity-consistent estimator for the covariance matrix, derived from quasi-Bayesian Monte Carlo simulation based on normal approximation.

We included 748 patients with confirmed COVID-19, with a mean age of 51.22±13.62 . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint Median EAT thickness was 9.67mm (IQR 7.67-12.0), median sub thoracic fat thickness was 16mm (IQR 11.0-23.0) and pericardial fat was present in 451 patients (60.5%).

Cases that required mechanical ventilation had greater EAT thickness, pericardial fat volume and BMI with no significant difference in subthoracic adipose tissue thickness. In fatal cases, EAT thickness and pericardial fat volume were significantly higher; BMI was greater but failed to reach statistical significance and sub thoracic fat was no different between fatal and non-fatal cases (Figure 1) . When stratifying cases according to BMIdefined obesity, those who had increased EAT were older, had worsened respiratory parameters, altered coagulation and overt inflammation, and had higher rates of severe outcomes and intubation as well as higher mortality scores independent of BMI status ( Table 1) . EAT thickness was independently associated with male gender (β=-0.236, 95%CI -0.382,-0.090), oxygen saturation (β=-0.014, 95%CI -0.019,-0.008) and higher 4C mortality scores (β=0.063, 95%CI 0.039, 0.087, adjusted R 2 =0.103). In a second model, EAT thickness was associated with increased levels of ultrasensitive cardiac troponins (β=0.0002, 95%CI 0.00005, 0.0004), BMI (β=0.034, 95%CI 0.021, 0.048) and age (β=0.017, 95%CI 0.011, 0.023, adjusted R 2 =0.081), even after adjustments for C-reactive protein levels.

Using Cox regression analysis, EAT thickness was a predictor of COVID-19 mortality, even after adjustment for age, gender, number of comorbid conditions and BMI ( Table 2) .

Using post-estimation simulation, we observed monotonic increases in mortality risk with increasing normalized EAT thickness both in obese and non-obese subjects (Figure 2) .

Subjects who had increased EAT had higher risk of both mortality and requirement for invasive mechanical ventilation. Similarly, after assessing the independent effect of other adipose tissue segments, pericardial fat volume was associated with increased mortality in . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; 1 0 univariate analyses but failed to retain significance after adjustments for age, gender, number of comorbid conditions and BMI. Similarly, sub thoracic fat thickness was associated with increased risk of mortality and mechanical ventilation after adjustment for age, gender, and number of comorbid conditions but after adjustment for BMI this association failed to maintain statistical significance. In contrast, BMI was associated with both mortality and invasive mechanical ventilation even after adjustment for covariates ( Table 2) EAT partially mediates the effect of age and BMI on COVID-19 mortality Given the association of BMI, increased cardiac troponins and chronological age on COVID-19 mortality levels and EAT thickness, two causal mediation models were explored. We explored EAT thickness as a mediator of both age and BMI and in increasing risk of COVID-19 mortality and critical COVID-19 ( Table 4) .

The second causal mediation model explored whether increased risk for COVID-19 outcomes was partially mediated by EAT-induced heart damage (Figure 3) . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) 1 1 increased EAT thickness increased risk for myocardial infarction in COVID-19 (OR 2.83, 95%CI 1.07-7.31), after adjustment for age, gender and comorbid conditions.

Here, we showed that EAT thickness is a significant predictor of COVID-19 severity and mortality independent of BMI, age, and comorbid conditions. Similarly, subjects with increased EAT had higher levels of COVID-19 severity markers independent of BMI.

Overall, EAT thickness was associated with decreased oxygen saturation, male gender, and increased COVID-19 severity; similarly, EAT thickness was associated with increased ultrasensitive cardiac troponin levels. Sub thoracic and pericardial adipose tissue did not show an increased risk for adverse outcomes or mortality independent of BMI. Notably, EAT thickness partly mediates the effect of age and BMI related risk on COVID-19 adverse outcomes. These findings confirm that adipose tissue distribution, in particular the presence of visceral adiposity more so than total adipose tissue, may play a significant role in modulating the adaptive responses to SARS-CoV-2 infection, and thus increase disease severity in COVID-19 13 .

The metabolic and inflammatory role of VAT and its role in cardiovascular and metabolic health is well documented 14 . Beyond the risk associated with whole-body adipose tissue as assessed by BMI, VAT depots significantly contribute to the increased cardiovascular risk profile and low-grade pro-inflammatory state observed in patients with obesity 15 .

Increased accumulation of VAT has been associated with increased deposition of ectopic fat, particularly in the liver and in the epicardium as EAT 16 . Notably, EAT shares microcirculation with the myocardium, favoring the rapid exchange of metabolic and inflammatory products 17 ; the implication of this anatomical relationship suggests that, under acute or chronic inflammatory conditions, these interactions might prove deleterious to cardiovascular function. Increased epicardial adipogenesis induces the secretion of proinflammatory adipokines which contribute to atrial and ventricular damage 7,12,17 . In the . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint setting of COVID-19, EAT is postulated to play a role in generating the imbalance between the production of anti and pro-inflammatory adipokines, thus contributing to the enhanced cytokine storm and multisystem involvement documented in severe COVID-19 8 . In this study, EAT thickness was a significant predictor of adverse biochemical profiles, critical COVID-19 and increased mortality independent of BMI.

Using mediation analyses, EAT thickness was shown to play a significant role in mediating the risk of critical COVID-19 and mortality attributable to increasing age and BMI. Other authors have shown that increased VAT deposition has a greater predictive value for adverse COVID-19 outcomes compared to BMI. This depot-specific adipose tissue dysfunction may be particularly relevant in younger cases [18] [19] [20] [21] . These results are consistent with previous findings in this population and further contribute to the characterization of the mechanisms underlying the risk attributable to aging and obesity in severe COVID-19 25-28 .

Finally, increased EAT accumulation was shown to be associated with increased cardiac damage and this may contribute to COVID-19 severity and mortality. Increased expression of ACE II in whole-body and visceral adipose tissue in persons with obesity has been proposed as a potential mechanism for increasing the risk of COVID-19 by promoting viral spread and shedding and by amplifying the inflammatory responses [22] [23] [24] . Increased risk of cardiovascular complications in COVID-19 has been associated with the pro-thrombotic and inflammatory adaptive responses to SARS-CoV-2 infection as well as direct damage to the myocardium 9,25,26 . Increased EAT thickness was associated with increased risk of inhospital myocardial infarction and was associated with increased cardiac troponin levels, possibly indicating direct cardiovascular injury. Since EAT is only a measure of ectopic fat deposition around the myocardium, its measurement can be considered complementary to BMI. Hence, it may be most useful to assess risk for potential cardiac involvement in COVID-19.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) 1 3 This work has certain strengths and limitations. The study analyses a large number of patients in whom EAT thickness was measured at admission and who were followed throughout hospitalization to record COVID-19 relevant outcomes. Furthermore, this work is novel as it assesses the different types of intrathoracic adipose tissue, including EAT, subthoracic and pericardialm in addition to whole-body adipose tissue measures such as BMI. Using mediation analyses, the degree of contribution of EAT in risk of critical disease and mortality was also quantified. Limitations include the use of EAT thickness instead of volume; this was because the CT scans on admission were simple scans in which volume could not be assessed. There were only a small number of recorded cardiovascular events, this means the full impact of EAT on COVID-19 cardiovascular complications could not be evaluated. The results only apply to moderate or severe infection as mild cases were not included dut to the nature of case recruitment. The study was carried out at a single COVID-19 centre, and the findings may not be representative at a population level.

Finally, since abdominal CT scans were not available for most patients, the contribution of thoracic vs. abdominal fat could not be assessed, an area which should be evaluated in future studies.

In conclusion, EAT thickness was associated with increased risk for critical COVID-19 and mortality compared to other types of intrathoracic adipose tissue. EAT was also associated with increased cardiac troponin levels, suggesting it may play a role in the risk for cardiovascular complications in COVID-19. Furthermore, EAT appears to be a mediator of the effect of age and BMI on adverse disease outcomes. Hence, this work adds to the body of evidence suggesting that EAT may be an important protagonist in adverse metabolic and inflammatory responses to SARS-CoV-2.

Nothing to disclose.

. CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; 1 4 FUNDING: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. . CC-BY-NC-ND 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. ; https://doi.org/10.1101/2021.03.14.21253532 doi: medRxiv preprint Table 1 . Comparison of demographic and clinical markers of COVID-19 patients comparing epicardial adipose tissue thickness (EAT) (increased >80 th sex-specific percentile or not) stratified by obesity status as defined by body-mass index (BMI).

Non-Obese is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

The copyright holder for this preprint this version posted March 24, 2021.

; https://doi.org/10.1101/2021.03.14.21253532

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