Edited by: Rajesh Puranik, Royal Prince Alfred Hospital, Australia
Reviewed by: Ciro Santoro, Federico II University Hospital, Italy; Carla Sousa, São João University Hospital Center, Portugal
This article was submitted to Cardiovascular Imaging, a section of the journal Frontiers in Cardiovascular Medicine
†These authors have contributed equally to this work
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Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic causing an escalating number of cases and fatalities worldwide. A large proportion of COVID-19 patients have comorbidities, with cardiovascular disease (CVD) being the most frequent. It was present in approximately 30–48% of patients (
This observational study was performed at the west branch of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology of Wuhan, China, which was a designated hospital to treat patients with COVID-19. We enrolled a total of 157 consecutive adult patients who were confirmed to have COVID-19 infection according to the WHO interim guidance from February 12, 2020 to March 16, 2020 (
Epidemiological, medical history, comorbidities, laboratory, treatment, and outcomes data were collected from electronic medical records. The data were analyzed by a trained team of physicians. The timing of laboratory measurements was within 3 days of echocardiographic examination with a mean interval of 1 day [interquartile range (IQR), 1–2]. The median time from admission to echocardiographic examination was 7 days (IQR, 3–11). Clinical outcomes (death or discharge) were monitored through to April 7th, 2020.
Underlying CVD included a history of hypertension, coronary artery disease, heart failure, cardiomyopathy, and arrhythmia. Acute cardiac injury was defined as serum levels of cardiac high-sensitivity troponin I (hs-TNI) above the 99th percentile upper reference limit.
Bedside echocardiography examinations were performed with an EPIQ 7C machine (Philips Medical Systems, Andover, MA, USA) at the designated COVID-19 isolation wards or intensive care units (ICU). Two-dimensional and Doppler echocardiography were performed in standard views according to the American Society of Echocardiography (ASE) guidelines (
Left ventricular (LV) ejection fraction (LVEF) and volumes were calculated using Simpson's biplane method. LV mass was calculated according to Devereux's formula. LV diastolic function was estimated using the ratio of early transmitral flow velocity (E) to the late transmitral flow velocity (A) and the ratio of transmitral E to the early diastolic LV septal tissue velocity (e′). LV systolic dysfunction was defined as a LVEF <50%, and LV diastolic dysfunction was determined according to the published guideline of the American Society of Echocardiography (ASE) and the European Association of Cardiovascular Imaging (EACVI) (
RV function was assessed by tricuspid annular plane systolic excursion (TAPSE), fractional area change (FAC), peak systolic velocity (S′) of the tricuspid lateral annulus, and myocardial performance index (MPI) (
Representative examples of RVFAC and TAPSE measurements from COVID-19 Patients without and with CVD.
Continuous numeric variables are expressed as mean ± SD or medians (interquartile range), and categorical variables are expressed as frequency (percentage). Continuous variables were compared using a two-sample
Clinical characteristics of patients with COVID-19 with and without CVD are shown in
Clinical characteristics of patients with COVID-19 infection with and without cardiovascular disease.
Age, years | 62 ± 13 | 66 ± 11 | 58 ± 14 | <0.001 |
Male, |
79 (50.3%) | 51 (57.3%) | 28 (41.2%) | 0.045 |
Body mass index, kg/m2 | 24.1 ± 3.1 | 24.0 ± 3.0 | 24.3 ± 3.1 | 0.445 |
Heart rate, beats/min | 90 ± 17 | 89 ± 16 | 92 ± 17 | 0.164 |
Respiratory rate, breaths/min | 25 ± 6 | 25 ± 6 | 25 ± 6 | 0.780 |
Systolic arterial pressure, mm Hg | 133 ± 81 | 138 ± 17 | 126 ± 17 | <0.001 |
Diastolic arterial pressure, mm Hg | 81 ± 12 | 82 ± 13 | 80 ± 10 | 0.096 |
Smoker, |
17 (10.8%) | 11 (12.4%) | 6 (8.8%) | 0.480 |
Hypertension, |
70 (44.6%) | 70 (78.7%) | 0 (0%) | <0.001 |
Diabetes, |
23 (14.6%) | 17 (19.1%) | 6 (8.8%) | 0.071 |
Obesity, |
24 (15.3%) | 15 (16.9%) | 9 (13.2%) | 0.532 |
COPD, |
9 (5.7%) | 6 (6.7%) | 3 (4.4%) | 0.534 |
Coronary artery disease, |
26 (16.6%) | 26 (29.2%) | 0 (0%) | <0.001 |
Heart failure, |
4 (2.5%) | 4 (4.5%) | 0 (0%) | 0.077 |
Arrhythmia, |
6 (3.8%) | 6 (6.7%) | 0 (0%) | 0.029 |
Chronic kidney disease, |
3 (1.9%) | 2 (2.2%) | 1 (1.5%) | 0.725 |
Chronic liver disease, |
6 (3.8%) | 2 (2.2%) | 4 (5.8%) | 0.234 |
Malignancy, |
11 (7.0%) | 3 (3.4%) | 8 (11.8%) | 0.041 |
Lymphocyte count, ×109/L | 1.0 (0.6, 1.4) | 0.9 (0.5, 1.2) | 1.0 (0.7, 1.5) | 0.012 |
D-dimer, mg/L | 1.1 (0.4, 2.7) | 1.5 (0.4, 2.4) | 1.0 (0.5, 4.2) | 0.295 |
PT, s | 13.5 (12.5, 15.0) | 13.4 (12.6, 15.2) | 13.7 (12.5, 14.5) | 0.99 |
APTT, s | 37.4 (33.3, 44.6) | 38.0 (33.1, 45.6) | 37.0 (33.7, 42.2) | 0.555 |
CK-MB, U/L | 11 (8, 18) | 12 (8, 25) | 10 (8, 13) | 0.05 |
hs-TNI, ng/L | 4.8 (2.2, 31.2) | 10.6 (3.3, 53.7) | 2.7 (1.7, 7) | 0.043 |
BNP, pg/ml | 79.1 (35.7, 163.9) | 85.3 (34.6, 162.5) | 57.9 (38.7, 153.2) | 0.049 |
CRP, mg/L | 26.5 (3.7, 67.6) | 27.5 (7.1, 75.4) | 25.3 (2.8, 63.2) | 0.44 |
PCT, ng/ml | 0.08 (0.05, 0.20) | 0.10 (0.05, 0.20) | 0.07 (0.05, 0.21) | 0.244 |
IL-6, pg/ml | 5.2 (2.4, 20.7) | 8.9 (3.5, 21.6) | 4.6 (2.5, 21.7) | 0.269 |
PaO2:FIO2, mmHg | 232.0 (151.0, 268.97) | 212.1 (140.6, 241.5) | 254.0 (212.1, 330.5) | 0.016 |
Antiviral therapy, |
150 (95.5%) | 86 (96.6%) | 64 (94.1%) | 0.45 |
Antibiotic therapy, |
119 (75.8%) | 73 (82.0%) | 46 (67.6%) | 0.037 |
Glucocorticoid therapy, |
65 (41.4%) | 36 (40.4%) | 29 (42.6%) | 0.782 |
Intravenous immune globulin, |
56 (35.9%) | 37 (41.6%) | 19 (27.9%) | 0.089 |
Anticoagulant therapy, |
81 (51.6%) | 52 (58.4%) | 29 (42.6%) | 0.05 |
Diuretics, |
39 (24.8%) | 32 (36.0%) | 7 (10.3%) | <0.001 |
Beta-blockers, |
33 (21.0%) | 28 (31.5%) | 5 (7.4%) | <0.001 |
Calcium channel blockers, |
48 (30.6%) | 43 (48.3%) | 5 (7.4%) | <0.001 |
ACE-I/ARB, |
17 (10.8%) | 15 (16.9%) | 2 (2.9%) | 0.005 |
Oxygen therapy, |
139 (88.5%) | 83 (93.3%) | 56 (82.3%) | 0.034 |
High-flow oxygen, |
90 (57.3%) | 61 (68.5%) | 29 (42.6%) | 0.001 |
Mechanical ventilation, |
37 (23.6%) | 27 (30.3%) | 10 (14.7%) | 0.022 |
IMV, |
26 (16.6%) | 19 (21.3%) | 7 (10.3%) | 0.065 |
NIMV, |
11 (7.0%) | 8 (9.0%) | 3 (4.4%) | 0.266 |
ICU admission, |
27 (17.2%) | 20 (22.5%) | 7 (10.3%) | 0.045 |
Acute kidney injury, |
20 (12.8%) | 12 (13.5%) | 8 (11.8%) | 0.775 |
ARDS, |
64 (40.8%) | 47 (52.8%) | 17 (25.0%) | <0.001 |
Acute heart injury, |
48 (20.6%) | 35 (39.3%) | 13 (19.1%) | 0.006 |
Coagulation dysfunction, |
29 (18.5%) | 19 (21.3%) | 10 (14.7%) | 0.288 |
DVT, |
63 (40.1%) | 42 (47.2%) | 21 (30.9%) | 0.039 |
Shock, |
1 (0.6%) | 1 (1.1%) | 0 (0%) | 0.567 |
Discharge, |
134 (85.4%) | 69 (77.5%) | 65 (95.6%) | 0.002 |
Death, |
23 (14.6%) | 20 (22.5%) | 3 (4.4%) | 0.002 |
Echocardiographic characteristics of COVID-19 patients with and without CVD are depicted in
Echocardiographic characteristics of patients with COVID-19 with and without cardiovascular disease.
LA dimension, mm | 35.4 ± 5.5 | 36.7 ± 5.9 | 33.3 ± 4.3 | <0.001 |
LV dimension, mm | 45.7 ± 5.1 | 45.7 ± 5.0 | 45.7 ± 5.2 | 0.967 |
IVS, mm | 9.6 ± 1.2 | 9.7 ± 1.3 | 9.5 ± 1.0 | 0.125 |
PW, mm | 9.1 ± 1.3 | 9.2 ± 1.4 | 8.9 ± 1.2 | 0.291 |
LVMI, g/m2 | 86.9 ± 21.0 | 88.4 ± 23.4 | 84.7 ± 16.9 | 0.331 |
Mitral DT, ms | 203 ± 55 | 206 ± 53 | 200 ± 58 | 0.561 |
Mitral E/A | 0.91 ± 0.36 | 0.88 ± 0.33 | 0.96 ± 0.39 | 0.473 |
Mitral E/e′ | 9.2 ± 3.2 | 9.7 ± 3.4 | 8.5 ± 2.8 | 0.043 |
LVEDVI, ml/m2 | 51.3 (43.8, 62.5) | 53.5 (43.0, 64.7) | 50.7 (44.0, 58.0) | 0.173 |
LVESVI, ml/m2 | 19.3 (15.6, 25.7) | 21.7 (15.6, 28.1) | 18.6 (15.6, 23.8) | 0.085 |
LVEF, % | 63.4 ± 7.0 | 62.5 ± 8.3 | 64.7 ± 4.7 | 0.063 |
Moderate-severe MR, |
6 (3.9%) | 5 (5.6%) | 1 (1.5%) | 0.179 |
RA dimension, mm | 35.8 ± 5.0 | 36.6 ± 5.3 | 34.9 ± 4.4 | 0.042 |
RV dimension, mm | 34.6 ± 5.5 | 34.9 ± 5.6 | 34.2 ± 5.3 | 0.390 |
Tricuspid E/A | 0.96 ± 0.29 | 0.92 ± 0.29 | 1.0 ± 0.29 | 0.134 |
Tricuspid E/e′ | 5.5 ± 1.8 | 5.7 ± 1.7 | 5.2 ± 2.0 | 0.577 |
TAPSE, mm | 22.2 ± 3.8 | 21.5 ± 3.7 | 23.2 ± 3.9 | 0.007 |
RV FAC, % | 47.5 ± 6.8 | 46.0 ± 5.3 | 49.3 ± 7.3 | 0.009 |
S′, cm/s | 13.5 ± 3.2 | 13.4 ± 3.1 | 13.5 ± 3.4 | 0.946 |
RV MPI | 0.46 ± 0.14 | 0.48 ± 0.16 | 0.43 ± 0.10 | 0.011 |
Moderate-severe TR, |
6 (3.9%) | 5 (5.6%) | 1 (1.5%) | 0.179 |
PASP, mmHg | 32 (24, 47) | 42 (27, 50) | 28 (24, 39) | 0.033 |
At the time of echocardiographic examination, 27 (30%) COVID-19 patients with CVD were treated with mechanical ventilation. These mechanically ventilated patients had decreased TAPSE and RVFAC and higher PASP, suggesting impaired RV function (
Echocardiographic findings in COVID-19 patients with CVD stratified by hs-TNI level are shown in
Clinical and echocardiographic characteristics of COVID-19 patients with CVD stratified by hs-TNI level.
Age, years | 65 ± 11 | 68 ± 10 | 0.185 |
Male, |
27 (46.6%) | 24 (77.4%) | 0.003 |
Body mass index, kg/m2 | 23.8 ± 2.9 | 24.2 ± 3.3 | 0.629 |
Heart rate, beats/min | 88 ± 17 | 91 ± 15 | 0.426 |
Respiratory rate, times/min | 25 ± 6 | 25 ± 7 | 0.637 |
Systolic arterial pressure, mm Hg | 139 ± 18 | 134 ± 16 | 0.216 |
Diastolic arterial pressure, mm Hg | 83 ± 13 | 80 ± 13 | 0.236 |
CK-MB, U/L | 10 (7, 14) | 22 (13, 33) | 0.072 |
BNP, pg/ml | 53.2 (26.6, 111.8) | 138.6 (86.9, 279) | 0.062 |
CRP, mg/L | 16.2 (4.2, 16.2) | 62.9 (22.7, 124.5) | 0.002 |
PCT, ng/ml | 0.07 (0.05, 0.11) | 0.21 (0.08, 0.40) | 0.003 |
IL-6, pg/ml | 4.5 (3.0, 14.8) | 14 (10.5, 71) | 0.126 |
D-dimer, mg/L | 0.9 (0.3, 2.1) | 1.7 (0.9, 3.0) | 0.262 |
LA dimension, mm | 35.7 ± 5.2 | 38.6 ± 6.5 | 0.029 |
LV dimension, mm | 45.7 ± 4.9 | 45.8 ± 5.3 | 0.913 |
IVS, mm | 9.8 ± 1.2 | 9.7 ± 1.5 | 0.653 |
PW, mm | 9.0 ± 1.4 | 9.4 ± 1.3 | 0.206 |
LVMI, g/m2 | 87.4 ± 20.5 | 90.2 ± 28.3 | 0.628 |
Mitral E/A | 0.82 ± 0.29 | 0.97 ± 0.38 | 0.050 |
Mitral E/e′ | 9.1 ± 3.0 | 10.5 ± 3.9 | 0.084 |
LVEDVI, ml/m2 | 53.0 (42.1, 68.8) | 53.5 (45.5, 62.5) | 0.079 |
LVESVI, ml/m2 | 21.6 (16.0, 31.1) | 23.4 (15.0, 25.3) | 0.061 |
LVEF, % | 61.6 ± 8.9 | 64.2 ± 6.8 | 0.203 |
RA dimension, mm | 35.6 ± 4.6 | 38.1 ± 6.1 | 0.038 |
RV dimension, mm | 34.2 ± 5.3 | 36.1 ± 6.0 | 0.134 |
Tricuspid E/A | 0.92 ± 0.30 | 0.92 ± 0.30 | 0.985 |
Tricuspid E/e′ | 4.8 ± 2.2 | 5.5 ± 2.4 | 0.147 |
TAPSE, mm | 22.2 ± 3.7 | 20.1 ± 3.3 | 0.013 |
RVFAC, % | 47.2 ± 6.1 | 43.6 ± 5.0 | 0.020 |
S′, cm/s | 13.5 ± 3.3 | 13.4 ± 2.8 | 0.855 |
RV MPI | 0.45 ± 0.14 | 0.54 ± 0.17 | 0.018 |
PASP, mmHg | 32 (26, 40) | 47 (34, 56) | 0.009 |
Clinical characteristics of survivors and non-survivors among CVD patients are presented in
Echocardiographic characteristics of survivors and non-survivors among CVD patients are depicted in
Echocardiographic characteristics of COVID-19 patients with CVD stratified by vital status.
LA dimension, mm | 36.7 ± 5.9 | 36.2 ± 6.2 | 38.3 ± 4.3 | 0.035 |
LV dimension, mm | 45.7 ± 5.0 | 46.0 ± 5.1 | 44.9 ± 4.6 | 0.460 |
IVS, mm | 9.7 ± 1.3 | 9.9 ± 1.3 | 9.4 ± 1.3 | 0.230 |
PW, mm | 9.2 ± 1.4 | 9.1 ± 1.4 | 9.3 ± 1.2 | 0.853 |
LVMI, g/m2 | 88.4 ± 23.4 | 90.8 ± 24.6 | 80.4 ± 17.4 | 0.141 |
Mitral DT | 206 ± 53 | 210 ± 54 | 187 ± 45 | 0.142 |
Mitral E/A | 0.88 ± 0.33 | 0.80 (0.67, 1.00) | 0.72 (0.67, 0.80) | 0.110 |
Mitral E/e′ | 9.7 ± 3.4 | 9.7 ± 3.5 | 9.7 ± 3.0 | 0.713 |
LVEDVI, ml/m2 | 53.5 (43.0, 64.7) | 52.4 (40.3, 67.2) | 53.6 (46.4, 59.4) | 0.257 |
LVESVI, ml/m2 | 21.7 (15.6, 28.1) | 20.9 (15.8, 28.1) | 23.4 (14.6, 29.8) | 0.505 |
LVEF, % | 62.5 ± 8.3 | 61.7 ± 8.6 | 65.4 ± 6.6 | 0.083 |
Moderate-severe MR, |
5 (5.6%) | 2 (2.8%) | 3 (15%) | 0.073 |
RA dimension, mm | 36.6 ± 5.3 | 36.0 ± 5.1 | 38.1 ± 5.8 | 0.136 |
RV dimension, mm | 34.9 ± 5.6 | 33.4 ± 5.1 | 36.7 ± 6.7 | 0.198 |
Tricuspid E/A | 0.92 ± 0.29 | 1.0 ± 0.33 | 1.06 ± 0.24 | 0.502 |
Tricuspid E/e′ | 5.7 ± 1.7 | 5.9 ± 2.0 | 5.4 ± 1.3 | 0.618 |
TAPSE, mm | 21.5 ± 3.7 | 22.2 ± 3.5 | 19.1 ± 3.1 | 0.002 |
RV FAC, % | 46.0 ± 5.3 | 47.2 ± 5.6 | 41.6 ± 5.5 | 0.001 |
S′, cm/s | 13.4 ± 3.1 | 13.6 ± 3.3 | 12.9 ± 2.7 | 0.340 |
RV MPI | 0.48 ± 0.16 | 0.46 ± 0.15 | 0.54 ± 0.19 | 0.045 |
Moderate-severe TR, |
5 (5.6%) | 3 (4.3%) | 2 (10%) | 0.313 |
PASP, mmHg | 42 (27, 50) | 33 (27, 43) | 48 (34, 59) | 0.042 |
LV and RV function parameters were studied by a receiver operating characteristic (ROC) analysis to evaluate the probability of mortality. RV functional indices were associated with a higher risk of mortality in COVID-19 patients with CVD (
Receiver operating characteristic curves of RVFAC and TAPSE for adverse clinical outcome. RVFAC, right ventricular fractional area change; TAPSE, tricuspid annular plane systolic excursion.
Kaplan–Meier survival curves for mortality are displayed
Kaplan–Meier plots and contour plots of survival probability in hospitalized COVID-19 patients with CVD.
In univariate and multivariate Cox analysis, higher level of hs-TNI, TAPSE, and RVFAC were independent predictors of higher risk of mortality (
Univariate Cox regression analysis of clinical and echocardiographic parameters. Forest plot for association of clinical and echocardiographic parameters with mortality. Impact of clinical and echocardiographic indicators on mortality in COVID-19 patients with CVD. ACE-I, angiotensin-converting enzyme inhibitors; ARB, angiotensin II receptor blockers; CI, confidence interval; COVID-19, coronavirus disease 2019; CVD, cardiovascular disease; DM, diabetes mellitus; FIO2, fraction of inspiration oxygen; hs-TNI, hypersensitive troponin I; LVEF, left ventricular ejection fraction; RVFAC, right ventricular fractional area change; TAPSE, tricuspid annular plane systolic excursion; PaO2, partial pressure of oxygen.
Multivariate Cox regression analysis of clinical and echocardiographic parameters. Forest plot for association of clinical and echocardiographic parameters with mortality. Impact of clinical and echocardiographic indicators on mortality in COVID-19 patients with CVD. CI, confidence interval; COVID-19, coronavirus disease 2019; CVD, cardiovascular disease; hs-TNI, hypersensitive troponin I; RVFAC, right ventricular fractional area change; TAPSE, tricuspid annular plane systolic excursion.
Likelihood ratio test for the incremental prognostic value of TAPSE. The incremental value of TAPSE over clinical and RVFAC for the prediction of mortality. RVFAC, right ventricular fractional area change; TAPSE, tricuspid annular plane systolic excursion; hs-TNI, high-sensitivity troponin I.
To the best of our knowledge, this may be the first study describing the echocardiographic features and its prognostic value in patients with COVID-19 and CVD. COVID-19 patients with CVD displayed poorer LV diastolic and RV function than non-CVD patients. The most common cardiac abnormality in CVD patients was RV dysfunction, followed by LV diastolic dysfunction and LV systolic dysfunction. Furthermore, diminished RV function was associated with higher mortality in CVD patients, suggesting that RV measurements may be important for detecting COVID-19 patients with CVD who are at higher risk of mortality.
Consistent with a previous study, we found that COVID-19 patients with CVD had a significantly higher mortality compared to those without (
Our study showed that patients with COVID-19 infection and underlying CVD had impaired LV diastolic function. This is in keeping with the study of Li et al., which demonstrated that only subclinical LV diastolic impairment was identified in patients with severe acute respiratory syndrome (
Generally, the etiology of RV dysfunction in COVID-19 infection has not been well-established. In addition to myocardial injury, it is though that the RV dysfunction may be reflective of conditions that can increase RV afterload during this viral infection, including hypoxic pulmonary vasoconstriction, hypercarbia, excessive positive end-expiratory pressure (PEEP), pneumonia, elevated left atrial pressure, or combination of all these factors (
Considering that patients with COVID-19 infection and underlying CVD are more likely to have a more severe course of their illness and a poorer clinical outcome, it is imperative to identify this high-risk group for consideration of earlier or more intensive therapy. Thus far, some prognostic indicators of poor outcome, in particular elevated level of hs-TNI, have been recognized (
In our study, patients found to have reduced RV function by echocardiography were at higher risk of deterioration and death. Our results demonstrate that RV function serves as a novel imaging biomarker that predicts higher mortality in patients with COVID-19 infection and underlying CVD. These findings were consistent with our previous work showing that RV dysfunction predicted poorer outcome in unselected patients with COVID-19 (with or without CVD) (
Although our results demonstrated the presence of cardiac impairment in COVID-19 patients with underlying CVD, the time course for the development of these cardiac abnormalities remained unknown, as we did not have serial echocardiography available for these patients. Another limitation to consider is that although RV functional parameters were revealed to be important predictors of risk in this study, we only carried out the basic, commonly used measures of RV function such as TAPSE and RVFAC (
Finally, the main limitation of our study was that it was a single-center study, with a relatively limited sample size and a homogenous population. As a center designated to treat patients with COVID-19 in our region, our study subjects may not be representative of populations elsewhere, limiting extrapolation of our results. Future studies, involving larger sample sizes, multiple centers, and international collaboration, are needed to determine the true prognostic value of echocardiographic parameters in patients with COVID-19 infection and allow for further refinement of stratification by determinants such as sex, age, and ethnicity.
Right ventricular dysfunction is more common than LV dysfunction among COVID-19 patients with underlying CVD. Importantly, RV function parameters are associated with higher mortality, suggesting that RV measurement may serve as a novel imaging biomarker for the risk stratification of patients with COVID-19 infection and underlying CVD. The study highlights the importance of bedside cardiovascular ultrasound in the assessment and prognostication of hospitalized patients with COVID-19 infection.
The original contributions presented in the study are included in the article/
The studies involving human participants were reviewed and approved by Tongji Medical College, Huazhong University of Science and Technology. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.
Conception and design of the study: YL, LF, SZ, YX, JW, YY, QL, AJ, MX, and LZ. Acquisition of data: BW, LH, DZ, YoZ, and HY. Analysis and interpretation of data: CW, HL, WS, YaZ, ML, YC, and LC. Drafting the article: YL, LF, SZ, and YX. Revising the article: YL, LF, SZ, YX, LZ, and MX. Final approval of the article: SZ, YX, LY, and LZ. All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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