Cardiac involvement in COVID-19 patients: mid-term follow up by cardiac magnetic resonance imaging

Background: Coronavirus disease 2019 (COVID-19) induces myocardial injury, either direct myocarditis or indirect injury due to systemic inammatory response. Myocardial involvement has been proved to be one of the primary manifestations of COVID-19 infection, according to laboratory test, autopsy, and cardiac magnetic resonance imaging (CMRI). However, the middle-term outcome of cardiac involvement after the patients were discharged from the hospital is yet unknown. The present study aimed to evaluate mid-term cardiac sequelae in recovered COVID-19 patients by CMRI Methods: A total of 47 recovered COVID-19 patients were prospectively recruited and underwent CMRI examination in this study. The CMRI protocol consisted of black blood fat-suppressed T2 weighted imaging (BB-T2WI), T2 star mapping, left ventricle cine imaging, pre- and post-contrast T1 mapping, and late gadolinium enhancement (LGE). Myocardium edema and LGE were assessed in recovered COVID-19 patients. The left ventricle (LV) and right ventricle (RV) function and LV mass were assessed and compared with normal controls. Results: Finally, 44 recovered COVID-19 patients and 31 normal controls were included in this study. No edema was observed in any patient. LGE was found in 13 patients. All LGE lesions were located in the middle myocardium and/or sub-epicardium with a scattered distribution. Further analysis showed that LGE-positive patients had signicantly decreased left ventricle peak global circumferential strain (LVpGCS), right ventricle peak global circumferential strain (RVpGCS), right ventricle peak global longitudinal strain (RVpGLS) as compared to non-LGE patients (p (cid:0) 0.05), while no difference was detected between the non-LGE patients and normal controls. Conclusion: Myocardium injury existed in about 30% of COVID-19 patients. These patients had peak right ventricle strain that decreased at the 3-month follow-up. Cardiac MRI can monitor the COVID-19-induced myocarditis progression, and CMR strain analysis is a sensitive tool to evaluate the recovery of left ventricle circumferential contraction dysfunction and right ventricular dysfunction.


Introduction
Coronavirus disease 2019 (COVID-19) is a nascent pandemic. Until July 20, 2020, 14353494 con rmed cases, including 603703 deaths, were reported to the World Health Organization 1 . Data from previous studies suggested that acute cardiac injury occurred in 20% COVID-19 patients 2 . In hospitalized patients, the cardiac injury was up to 30% and caused 40% deaths [3][4][5][6] . The mechanisms of cardiac injury are direct myocarditis (direct myocardial infection by SARS-CoV-2) or indirect factors, such as cardiac stress due to respiratory failure, indirect injury from systemic in ammatory response-cytokine release syndrome, stress cardiomyopathy, or a combination of all these factors [6][7][8][9] .
Cardiovascular magnetic resonance imaging (CMRI) can visualize and quantify heart volume and function and characterize the myocardial tissue; thus, it has been used as a gold standard non-invasive imaging tool in cardiovascular medicine 10 . A recent single-center study from Wuhan demonstrated that more than half of the recovered COVID-19 patients sustain cardiac edema, brosis, and impaired right ventricle (RV) contractile function 11 . However, in this small-sample retrospective study, only patients with reported cardiac symptoms were included. The middle-term outcome of cardiac involvement in  patients is yet unknown. Thus, the present study aimed to evaluate mid-term cardiac sequelae in recovered COVID-19 patients by CMRI.

Study design and participants
For this prospective, single-center study, we recruited consecutive COVID-19 patients from May 8 to July 20, 2020. The inclusion criteria were as follows: (1) Patients were previously con rmed to have SARS-CoV-2 infection, (2) patients were recovered from COVID-19 and discharged from the hospital for 12 weeks, (3) patients agreed to participate in the study and signed informed consent. The exclusion criteria were as follows: (1) Patients has undergone pacemaker surgery, (2) patients with uncontrolled high blood pressure, (3) patients with coronary heart disease (evidence of coronary artery stenosis > 50%) or previous myocardial infarction, (4) patients with moderate to severe valvular dysfunction, (5) patients with previous atrial brillation, (6) previous heart failure, (7) previous myocarditis, (8) patients with known cardiomyopathy, (9) patients with severe renal insu ciency (creatinine clearance rate < 30 mL/min/1.73 m 2 , (9) patients who cannot cooperate with breath-holding and cannot undergo CMR examination, (10) pregnant women, (11) patients are not suitable as clinical subjects due to other factors.
Age-and sex-matched healthy controls, who underwent the cardiac MRI exams in our hospital previously, were selected from a health screening database. All the controls showed normal ECG, echocardiography, and cardiac MRI and did not present any cardiovascular disease or systemic in ammation. The present study was approved by the local institutional review board hospital (KS2020001), and informed consent was obtained from all patients.

MRI scanning protocol
All patients underwent MRI examinations on a 3T MR scanner (Ingenia CX, Philips Healthcare, Best, The Netherlands). The cardiac MRI protocol consisted of black blood fat-suppressed T2 weighted imaging (BB-T2WI), T2 star mapping, left ventricle cine imaging including four chambers, two-chamber, short axis, pre-and post-contrast T1 mapping, and late gadolinium enhancement (LGE).

MRI images analysis
Anonymized images were evaluated by two radiologists (HW and LX with 8 and 12 years of cardiac MRI diagnosis experience, respectively). Myocardium edema was de ned as the regional or global signal hyperintensity on T2WI 13 . Myocardial edema ratio (ER) was de ned as the ratio > 1.9 between myocardial signal intensity (SI) and skeletal muscle SI. High signal area of inadequately suppressed slow-owing cavitary blood was excluded carefully 14 . The LGE lesion was quanti ed using full width at half-maximum method 15 . The visual presence and different patterns (epicardial, mid-wall, or transmural) on the LGE images were assessed by two radiologists independently. Any discrepancies were resolved by reaching consensus through consultation. The ratio between the LGE volume and the total LV myocardium volume (LGE/myocardium) in the LGE-positive patients was calculated.
The left ventricle (LV) and RV function and LV mass were assessed based on the short-axis cine images using cvi42 software (Circle Cardiovascular Imaging Inc., Calgary, Canada). Endocardial and epicardial borders, with papillary muscles excluded from volumes, were identi ed automatically by the software and amended by a radiologist (WH). LV and RV range were de ned from the planes of the mitral valve and tricuspid valve to the apex, respectively, on 4-chamber cine images in both diastolic and systolic phases.
Short-axis images were divided into size-based equiangular segments with RV-LV junction as the reference point. LV and RV function parameters, end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), cardiac output (CO), ejection fraction (EF), and LV mass were calculated automatically. All volumes and masses were normalized to the body surface area (BSA).
Three-dimensional (3D) global radial strain (GRS), global circumferential strain (GCS), and global longitudinal strain (GLS) of LV and RV were obtained using cvi42. The end-diastolic phase served as the reference. Contours of endo-and epicardial myocardium of short-axis, as well as the 2-, 3-, 4-chamber long-axis cine images, were drawn by a radiologist (WH). Patients were further divided into two subgroups based on visual LGE.

Statistical analysis
All data were analyzed using SPSS software version 25.0 (SPSS Inc., Chicago, IL, USA). Normally distributed continuous variables were expressed as mean ± standard deviation. Two-tailed one-way ANOVA was used to analyze the differences between LGE, non-LGE, and normal control groups.
Categorical variables were expressed as counts and percentages. T-test was used to compare the means with normal distribution, and the Mann-Whitney U test was used to compare the variables with nonnormal distribution between LGE and non-LGE groups. χ 2 test was used to explore the statistical signi cance of CMR parameters among LGE, non-LGE, and normal control groups. A two-sided p < 0.05 was considered as statistically signi cant.

Population characteristics
From May 8 to July 20, 2020, 47 patients who recovered from COVID-19 were recruited in this study and were subjected to CMR examination. According to the CMR diagnosis, one patient was excluded because of moderate tricuspid regurgitation, one was excluded because of hypertrophic cardiomyopathy, and one was excluded because of hypertensive cardiomyopathy. Finally, 44 recovered patients and 31 normal controls were included in this study.

Myocardium edema and LGE
No edema (high signal intensity on T2WI) or myocardium hemorrhage was observed in any patient; however, LGE was detected in 13 patients. All LGE lesions were located in the middle myocardium and/or sub-epicardium with a scattered distribution (Fig. 1). Among a total of 208 myocardial segments in 13 patients, most LGE lesions were located at the inferior and inferior-lateral segments at the base and midchamber. The Bull's eye illustration (Fig. 2) shows us the number of myocardial LGE distributed in AHA 16 segments' model in all 13 patients. The inferior wall and inferior-lateral wall of the basal segment was the most frequently involved segment (10/12 patients). The median of LGE/myocardium ratio was 1.7% (1.1%-3.0%).
LV/RV morphological, function, and strain analysis Table 2 shows the values for global LV and RV morphological and functional parameters and the measurement of the 3D global CMR feature-tracking deformation parameters. Strikingly, no signi cant difference was detected in the LV and RV morphological parameters (EDV, ESV, and mass) among COVID-19 patients with and without LGE and normal controls. Although no signi cant difference was detected in the LV and RV traditional function parameters -EF, cardiac output (CO) , cardiac index (CI), stroke volume (SV); LV peak 3D-GCS were decreased in COVID-19 patients with visual LGE (-15.08 ± 10.33) on CMR images as compared to healthy controls (-19.39 ± 3.02) (p < 0.05). Both peak 3D GCS and GLS of RV in COVID-19 patients with LGE (-9.42 ± 3.44 and -7.75 ± 3.98, respectively) were signi cantly decreased as compared to COVID-19 patients without LGE (-12.08 ± 3.98 and -12.89 ± 3.01, respectively) and normal control (-12.85 ±4.33 and -11.30± 3.87, respectively) (both p 0.05). However, no difference (peak 3D GCS and GLS of RV) was detected between COVID-19 patients without LGE and the normal controls (p > 0.05).

Discussion
The present study found that about 30% (13 out of 44) of the COVID-19 patients had myocardium injury (manifested as LGE on CMR delay enhanced images) at the 3-month follow up, while no edema was observed. Further analysis showed that LGE-positive patients had a decrease in the LV GCS as compared to normal control and a signi cant decrease in the RV GCS, and GLS as compared to non-LGE patients.
Myocardial involvement has been proved to be one of the primary manifestations of COVID-19 infection by laboratory, autopsy, and CMR 16-18 as compared to other members of the coronavirus family 19 . A recent study demonstrated that in the recovered COVID-19 patients with cardiac symptoms, 54% had myocardium edema, and 31% had LGE 11 . In the current study, no edema was observed, which might indicate that all myocardial injury has passed the acute stage at the 3-month follow-up 13,20 . The persistence of visual LGE at 3-month follow-up re ecting necrosis (persistent in ammation) or scar ( brosis) might be caused by COVID-19 and needs to be elucidated further 21 . Yet, visual LGE indicated that up to 30% COVID-19 patients have irreversible myocardial injury 22,23 , which is consistent with the ndings of the previous study and can con rm one of the main mechanisms of COVID-19 induced direct myocardial injury-myocarditis [24][25][26] . In addition, the presence of LGE has been proven to be an independent predictor of all-cause mortality and cardiac mortality in myocarditis 27,28 . Since the LGE/myocardium ratio was small, the cardiac status of COVID-19 patients with LGE needs to be closely monitored.
All the LGE lesions were located in the middle myocardium and/or sub-epicardium, wherein the bers are oriented transversely, and the torque enhances shortening in the circumferential direction 29, 30 . This may be the reason for LV 3D GCS to be oriented along the perimeter in short axis view 29 and decreased in the COVID-19 patients with LGE. This nding prompts us to focus on the left ventricle circumferential contraction dysfunction in these patients in addition to impaired RV function.
Furthermore, impaired RV function has been demonstrated by either echocardiography or CMR 11, 31, 32 . RV strain has been recommended to assess the RV function in clinical scenarios with suspected RV dysfunction 33 . Although our results showed that the RV traditional morphological and function parameters are in a normal range, the RV strain in COVID-19 patients with LGE was signi cantly decreased as compared to those without LGE and normal controls. This phenomenon indicated that COVID-19 patients with LGE still had RV dysfunction, which could be detected by CMR strain analysis.
COVID-19 results in acute respiratory distress syndrome (ARDS) 34 and is frequently associated with RV dysfunction, increased pulmonary resistance 35 , increased values of systolic pulmonary arterial pressure, increased RV afterload 36, 37 , severe hypoxia, oxidative stress, and increased myocardial oxygen demand induced by ARDS 38 .
According to a recent systematic echocardiographic study, the most frequent abnormality induced by COVID-19 was RV dilation with or without dysfunction 35 . However, our results only showed RV dysfunction in patients with LGE. No RV morphological (EDV and ESV) difference was detected at the 3month follow up, which might be attributed to improved pneumonia; subsequently, the RV rapidly returns to normal size while the RV strain is still decreased.
Limitations Nevertheless, the current study has some limitations. First, the lack of baseline CMR examination limits the evaluation of the progress of heart involvement. Second, the sample size was small. Third, the majority of the included patients had moderate and severe COVID-19, and hence, our study could not re ect the full spectrum of critical COVID-19 patients. Fourth, we had data of only a 3-month MRI examination, and thus, a long-time follow-up is essential to determine the progression or regression of cardiac involvement.

Conclusions
Myocardium injury existed in about 30% of the COVID-19 patients, who also had left ventricle circumferential strain and right ventricle strain that decreased at the 3-month follow-up. Cardiac MRI can monitor the COVID-19-induced myocarditis progress. CMR strain analysis is a sensitive tool to evaluate the recovery of left ventricle circumferential contraction dysfunction and right ventricular dysfunction. The study was approved by the local committees, and all patients gave informed consent for their medical data to be used in this study.

Consent for publication
The manuscript is approved by all authors for publication Availability of data and material The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request. LGE: late gadolinium enhancement