Systemic Arterial Function after Multisystem Inflammatory Syndrome in Children Associated with COVID-19

: Introduction: Multisystem inflammatory syndrome in children (MIS-C) is a new disease entity occurring in the pediatric population two to six weeks after coronavirus exposure due to a systemic arteritis. We investigated post-hospital-discharge arterial function at short-and mid-term intervals using pulse wave velocity. We assessed associations between arterial function, left ventricular diastolic and systolic function and left ventricular mass. Materials and methods: Retrospective data collection was carried out on 28 patients with MIS-C with at least two outpatient pediatric cardiology clinic visits post hospital admission. The patients underwent assessment of systemic arterial function and cardiac function. Data included pulse wave velocity between carotid and femoral arteries and echocardiographic assessment of left ventricular systolic function (shortening and ejection fraction, longitudinal strain), diastolic function and left ventricular mass. Results: Pulse wave velocity significantly decreased from visit 1 to visit 2 (5.29 ± 1.34 m/s vs. 4.51 ± 0.91 m/s, p = 0.009). Left ventricular mass significantly decreased from visit 1 to visit 2 (42 ± 9 g/m 2.7 vs. 38 ± 7 g/m 2.7 , p = 0.02). There was a significant negative correlation between the pulse wave velocity and E/A mitral inflow ( − 0.41, p < 0.05). Conclusions: Children have elevated pulse wave velocity and left ventricular mass in the short-term relative to mid-term values after hospital discharge. These results suggest that MIS-C is associated with transient systemic arterial dysfunction, which, in turn, may play a role in cardiac changes.


Introduction
A novel coronavirus was identified in late 2019 that rapidly reached pandemic proportions.The World Health Organization designated the official name for the disease coronavirus disease 2019 (COVID-19) and named the responsible virus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1].Subsequently, a new disease entity, multisystem inflammatory syndrome in children (MIS-C), was identified as a severe hyperinflammatory condition occurring between 2 and 6 weeks after acute infection with COVID-19 [2][3][4].Initially, the patients presenting with this hyperinflammatory syndrome had fever and mucocutaneous manifestations similar to those of Kawasaki's Disease (KD), an acute febrile mucocutaneous lymph node syndrome with systemic vasculitis [5,6].KD has been associated with systemic artery endothelial dysfunction occurring later in life, with the potential for early progression to atherosclerosis [7].The similarities between MIS-C and KD suggest that the etiology of MIS-C is a generalized vasculitis, specifically an arteritis affecting multiple organ systems [8].Pulse wave velocity (PWV) is an accepted method for assessing arterial function.Patients with a history of KD have a significantly higher normal predicted value of and a subsequent tendency for increased arterial stiffness [9].In addition, pulse wave velocity has been used to show an increase in arterial stiffness in adult COVID-19 patients [10][11][12][13].
Little is known about arterial function in children with MIS-C.The aim of this study was to investigate pulse wave velocity in the short-and mid-term following MIS-C.Our hypothesis was that in children recovering from MIS-C, PWV is elevated relative to subsequent values and that PWV derangement is associated with poorer left ventricular [LV] systolic and diastolic function along with elevated LV mass during these time periods.

Case Definition
MIS-C was diagnosed using the 2020 case definition from the Centers for Disease Control and Prevention (CDC) [14] (Appendix A).Definitions of organ dysfunction were based upon an early surveillance project initiated in 2020 with specific parameters defined in a supplemental appendix in that publication [2].In 2023, the Council of State and Territorial Epidemiologists (CSTE) and CDC updated the MIS-C case definition.The new clinical criteria for cardiac involvement were refined to include left ventricular ejection fraction <55% or coronary artery dilatation, aneurysm, or ectasia, or troponin elevated above laboratory normal range [15] (Appendix B).

Subjects
Retrospective observational data collection was carried out on 28 patients completing at least 2 outpatient pediatric cardiology clinic visits post hospital admission for MIS-C at a single, pediatric tertiary medical center.The patients were admitted with a diagnosis of MIS-C and with evidence of cardiac involvement as manifested by either left ventricular dysfunction, coronary artery dilatation, elevated serum troponin and/or elevated serum brain natriuretic peptide.Patients were subsequently followed up with 2 cardiology outpatient clinic visits, undergoing pulse wave velocity and echocardiography testing as part of clinical management.

Arterial Function
Systemic arterial function was assessed by pulse wave velocity using the SphygmoCor XCEL (ATCOR, Naperville, IL, USA).Pulse wave velocity testing was obtained with the patient in a resting, quiet, supine position with legs uncrossed.The patient was discouraged from talking or moving for 5 min prior to the test and during the test.Four consecutive brachial pressures were obtained.The tonometer was placed on the carotid artery and waveforms were obtained simultaneously with the inflation of a femoral cuff placed on the patient's upper thigh.Quality waveforms are simultaneously acquired for 10 s at both sites and a report is generated.Quality waveforms are determined by checking that signal strengths are above threshold markers, all guidance bars on the machine are green, and the waveforms are smooth and tall with a clearly defined 'foot'.Carotid-femoral pulse wave velocity methodology is considered the gold-standard measurement of arterial stiffness and was used by the team [16].Pulse wave velocity testing was routinely interpreted by a single investigator (TRK).

Echocardiography
Left ventricular systolic function was assessed by both left ventricular ejection fraction and left ventricular shortening fraction.Ejection fraction, shortening fraction and LV strain were all selected as measurements to strengthen the results related to systolic function.Biplane left ventricular ejection fraction was assessed using the modified Simpson's method after obtaining images of the left ventricle from the parasternal short axis and the apical 4-chamber views.Shortening fraction was calculated from the parasternal short axis view at the level of the papillary muscles from the M mode echocardiogram [17].Left ventricular global longitudinal myocardial strain was measured from the apical two-and four-chamber views and the parasternal short axis view at the level of the mitral valve leaflet tips [17].
Left ventricular diastolic function was assessed from mitral valve Doppler flow velocities (E and A wave) as well as mitral valve Doppler annular velocities (E ′ and A ′ ).The E and A waves were derived by measuring the flow through the mitral valve in the apical four-chamber view using pulsed wave Doppler, ensuring that the sample volume was placed at the mitral valve tips and aligned parallel to the flow as demonstrated by color Doppler echocardiography.The E/A mitral inflow wave ratio was calculated.The E ′ and A ′ waves were derived by tissue Doppler echocardiographic assessment of both the lateral (E ′ and A ′ lateral) and septal (E ′ and A ′ septal) walls in the myocardium adjacent to the mitral valve leaflet hinge points.These were obtained with the sample volume oriented parallel to mitral annular motion.The E ′ /A ′ lateral and E ′ /A ′ septal ratios were calculated.In addition, the E/E ′ lateral and the E/E ′ septal were calculated and served as a non-invasive estimate of left ventricular end-diastolic pressure [18].
Left ventricular diastolic function was also assessed by measuring left atrial volume by the area-length method.Left atrial area and long axis dimension were measured in both the apical 4-and 2-chamber views.Left atrial volume was calculated [19].
Left ventricular mass was calculated from the left ventricle measurements obtained from the parasternal long axis and using the formula of Devereaux et al., and the LV mass was indexed to height using allometric power of 2.7 [20].

Statistical Analysis
Descriptive statistics were used to describe the characteristics of the study cohort.All data were expressed as mean ± standard deviation.Differences in variables between clinic visit 1 and clinic visit 2 were assessed by paired Student's t test.Univariate correlation analysis was performed between pulse wave velocity and the indices of systolic function, diastolic function and left ventricular mass.Statistical significance level was set at a p value of <0.05.Inter-and intra-observer variability was assessed by correlation analysis.All analyses were performed using SAS (Windows version 9.3; SAS Institute, Cary, NC, USA) and/or the statistical program R version 4.0.2(https://www.r-project.org/).

Demographics
Patients were subsequently followed up with two cardiology outpatient clinic visits, receiving pulse wave velocity and echocardiography for clinical management.Hospital admission occurred between May 2020 and September 2022.A total of 53 patients were identified.Twenty-five patients were missing a value for mean pulse wave velocity at either clinic visit and were excluded, leaving a study population size of 28.
Fourteen (50%) patients received care in the intensive care unit.All twenty-eight patients had cardiac involvement as defined by one or more of the following findings: dilated coronary arteries, ejection fraction < 55%, elevated Troponin I, and elevated NT-proBNP.Twenty-two (79%) patients met the Council of State and Territorial Epidemiologists and Centers for Disease Control and Prevention criteria for a clinical diagnosis of cardiac organ involvement exhibiting one or more of the following findings: dilated coronary arteries, ejection fraction < 55% or elevated Troponin I. Of the 25 patients who were excluded because of missing values for mean pulse wave velocity during outpatient pediatric cardiology follow-up, there were more girls but no other significant differences in age, race, and BMI were observed compared to the study population.Eleven (44%) patients received care in the intensive care unit.All 25 patients had cardiac involvement as defined by one or more of the following findings: dilated coronary arteries, ejection fraction < 55%, elevated Troponin I, and elevated NT-proBNP.Fourteen (56%) patients met the Council of State and Territorial Epidemiologists and Centers for Disease Control and Prevention criteria for a clinical diagnosis of cardiac organ involvement exhibiting one or more of the following findings: dilated coronary arteries, ejection fraction < 55%, and elevated Troponin I. Excluded patients had the following measurements recorded on their initial clinic visit: left ventricular mass/ht 2.7 (40.9 ± 9.75); left atrial volume (30.4 ± 14.1); E/A mitral inflow (1.95 ± 0.56); and E ′ /A ′ lateral (3.0 ± 0.82).
Patients were predominantly healthy prior to hospital admission.Prior medical history (PMH) of the study sample was no PMH for 23 patients; asthma for 3 patients; anxiety for 1 patient; and eczema for 1 patient.Medications at clinic visit 1 were as follows: steroid and aspirin for 10 patients; steroid, aspirin, enalapril for 1 patient; Lasix and aspirin for 1 patient; and aspirin for 16 patients.Medications at clinic visit 2 were as follows: steroid and aspirin for 1 patient; aspirin for 22 patients; and no medications for 5 patients.

Inter-Observer/Intra-Observer Correlations for Echocardiographic Metrics
For the purposes of this study, inter-and intra-observer variability were calculated.The inter-and intra-observer correlations for metrics of systolic and diastolic function as well as cardiac structure are high, with an average of 0.88 for inter-observer correlation, and an average of 0.86 for intra-observer correlation.The correlations were obtained in an echocardiography laboratory that limits interpretation to a small group of pediatric cardiologists who have an additional year of cardiology fellowship and includes one investigator (TRK).

Discussion
The significant finding in this study is that arterial function, as assessed by pulse wave velocity, is elevated in the post-discharge short-term relative to the mid-term in children following cardiac derangement due to acute MIS-C.This finding is significant because it supports the hypothesis and data suggesting that the underlying pathologic mechanism for MIS-C is an arteritis affecting multiple organ systems which improves over time.Perhaps more importantly, our data suggest that although pulse wave velocity improves over time, it still outlasts the acute illness.This finding indicates the need for longer-term outcome studies.Understanding the etiology can help inform the treatment strategy for MIS-C.
The significant change in left ventricular mass and borderline significant change in left ventricular strain would support the acute heart failure symptoms occurring in our patients necessitating hospital admission.Acute changes in left ventricular mass may be due to myocardial edema in the acute phase of MIS-C, which resolves in the mid-term.Steroid administration during the hospital stay and immediately after discharge may contribute to elevated LV mass.The negative correlation between pulse wave velocity and E/A mitral inflow suggests that an arteritis, possibly a coronary arteritis, may result in subtle diastolic dysfunction.
Mean PWV at clinic visit 1 was 5.29.Reference values for PWV in the literature describe a range of 4.396 to 4.740 for a similar age range [21].Our technique used an applanation tonometry technique for measurement of PWV.Comparison of published PWV reference values describes lower mean PWV values for applanation tonometry techniques as compared to occlusive oscillometric arteriography techniques [22].

Similarities to Kawasaki Disease
The manifestation of MIS-C is severe systemic inflammation with multiple organ dysfunction.Cardiovascular organ dysfunction is common.Initial comparisons to KD have guided management and follow-up.The similarities in physiology between the two diseases are based on the profound systemic vascular inflammation that occurs, primarily in medium-sized arteries, resulting in acute presenting symptoms such as fever, rash, conjunctivitis, decreased appetite, diarrhea, and irritability [23].However, in MIS-C, there is an elevated incidence of additional organ system involvement, including nephrogenic, hematologic and neurologic systems with subsequent risk of acute kidney injury, thrombosis and seizures [2,24].The similarities in both diseases also include similar cardiac findings such as myocarditis with/without chamber enlargement or ventricular dysfunction, arrhythmias, and diastolic dysfunction [2,24,25], but the coronary abnormalities such as dilation and aneurysms are the most concerning and long-term findings associated with both diseases.Although a specific cause for KD remains elusive, the acute and chronic cardiovascular effects have been well described [5,25], including the premature development of coronary artery disease in patients with persistent coronary abnormalities [7,26].Additionally, aortic integrity has been demonstrated to have abnormal biophysical properties in KD patients, despite the resolution of vasculitis [27].These abnormalities in a similar systemic vasculitis disease lead us to question whether MIS-C will have similar long-term vascular implications.

Possible Etiologies of Multisystem Inflammatory Syndrome in Children
In contrast to patients with COVID-19, patients with MIS-C exhibit immune cell activation of multiple lineages with widespread interferon and inflammasome signaling, greater T cell activation and broad humoral immune response to common viruses and SARS-CoV-2 [28].Unlike KD, the inflammation in MIS-C is not felt to be mediated by IL-17A and the level of biomarkers associated with arteritis and coronary artery disease is lower [29].

Utility of Pulse Wave Velocity
Pulse wave velocity can provide important information related to cardiovascular disease in adults.Arterial stiffness, measured as the aortic pulse wave velocity (pulse wave velocity) between the carotid and femoral arteries, and subsequent microvascular dysfunction are predictors of future cardiovascular events [30,31].Post-COVID-19 adult patients had a higher aortic pulse wave velocity when compared to patients with atherosclerotic cardiovascular diseases and healthy controls [10].In one study, the results comparing testing at 4 months and 12 months post COVID-19 in adult patients show that pulse wave velocity remained similar and was significantly increased compared to controls [12].These findings were replicated in another study in which post-COVID-19 adult patients had higher values of pulse wave velocity when compared with healthy controls [13].Healthy adult subjects had higher pulse wave velocity and clinically significant progression of vascular impairment within 2-3 months of COVID-19 infection as compared to their pre-COVID 19 state [32].Compared to controls, patients with KD had higher pulse wave velocity [9,31].The addition of pulse wave velocity testing could further identify pediatric patients who may be vulnerable to the development of cardiovascular disease.Arterial stiffness in pediatric populations is increasingly measured with pulse wave velocity [33,34].Our study is the first to show that even children with multisystem inflammatory syndrome in children have differences in pulse wave velocity in the short-term compared to mid-term after infection.

Limitations
The limitations of our study include a small sample size for analysis and lack of pulse wave velocity testing during the acute phase during the inpatient hospital stay.The retrospective nature of the study resulted in missing variables, particularly as they relate to diastolic function.Patient attrition contributed to a lack of two clinic visits.Retrospective data collection prevented the use of technical protocols for the imaging defining measurements and calculations.Although patient exclusion was solely due to the lack of two pulse wave velocity measurements, our study population demonstrated higher percentiles of patients with decreased systolic function and elevated Troponin I.These findings contributed to a higher percentile of patients meeting the more stringent Council of State and Territorial Epidemiologists and Centers for Disease Control and Prevention criteria for cardiac organ involvement.Therefore, our results may not be generalizable to the at-large multisystem inflammatory syndrome in children population and only be relevant to the patients who were more acutely ill.A final limitation is the lack of a control group which limits our ability to state that there is, in fact, arterial dysfunction.However, we compared our data to published normal values [21,22,35,36].
This comparison showed that our Study 1 pulse wave velocity measurements are at least at the upper limits of normal if not frankly outside the 97th percentile of some of these control studies.Finally, since the population in this study is small, the results should be validated in a larger, possibly multi-institutional study.

Conclusions
In conclusion, this study demonstrates that systemic arterial function immediately after hospitalization for cardiac derangement due to COVID-19 is elevated relative to mid-term.These results support the hypothesis that multisystem inflammatory syndrome in children is due to a systemic arteritis.In addition, our results suggest that arteritis may result in subtle diastolic dysfunction.Pulse wave velocity should be considered during follow-up surveillance.Patients with a history of multisystem inflammatory syndrome in children potentially have an increased risk for arterial stiffness; however, further studies are needed to determine whether or not there will be longer-term effects on cardiovascular health, such as is seen in KD. a.
OR troponin elevated above laboratory normal range or indicated as elevated in a clinical note.
OR inflammation of the oral mucosa (e.g., mucosal erythema or swelling, drying or fissuring of the lips, strawberry tongue).c.
OR conjunctivitis or conjunctival injection (redness of the eyes).d.
Gastrointestinal involvement indicated by: a. Abdominal pain.b.
OR vomiting.c.
OR diarrhea.
Laboratory Criteria for SARS-CoV-2 Infection • Detection of SARS-CoV-2 RNA in a clinical specimen up to 60 days prior to or during hospitalization, or in a post-mortem specimen using a diagnostic molecular amplification test (e.g., polymerase chain reaction [PCR].

•
OR detection of SARS-CoV-2 specific antigen in a clinical specimen up to 60 days prior to or during hospitalization, or in a post-mortem specimen.

•
OR detection of SARS-CoV-2 specific antibodies in serum, plasma, or whole blood associated with current illness resulting in or during hospitalization.
Epidemiologic Linkage Criteria Close contact with a confirmed or probable case of COVID-19 disease in the 60 days prior to the hospitalization.
Vital Records Criteria A person whose death certificate lists multisystem inflammatory syndrome in children or multisystem inflammatory syndrome as an underlying cause of death or a significant condition contributing to death.

Table 1 .
Demographics and clinical information.

Table 2 .
Pulse wave velocity and echocardiographic indices of left ventricle function.