As of December 21, 2021, 273 million confirmed Coronavirus Disease-19 (COVID-19) cases, and 5.3 million deaths were reported globally (1). Centers for Disease Control and Prevention (CDC) issued an advisory in May 2020 about the symptoms of the multisystem inflammatory syndrome in children (MIS-C) which is characterized by a hyperinflammatory syndrome with multiorgan dysfunction (2). This syndrome is also known as pediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2, or pediatric multisystem inflammatory syndrome.

The current estimated incidence of MIS-C was estimated to be approximately 316 per 1,000,000 individuals < 21 years of age infected with COVID-19 (3). By the end of November 2021, CDC has received reports of nearly 6,000 MIS-C cases in the United States (4). More than 80% of patients with MIS-C present with cardiac involvement, including cardiac dysfunction, myocarditis, coronary artery abnormalities, valve regurgitation, pleural effusions, and cardiac arrhythmias (5).

Recently published articles summarize various similarities between MIS-C and Kawasaki disease (KD) (6, 7). Among children in developed countries, KD is the most common form of acquired cardiac disease (8). The estimated incidence of 250 cases per 1,000,000 children < 5 years in the North America. KD can lead to infiltration of inflammatory cells into medium-sized arteries, particularly the coronary arteries, with a risk of myocardial infarction and sudden death. In the acute phase, both MIS-C and KD have elevated cardiac markers, such as N-terminal pro-brain natriuretic peptide and troponin (9). Both MIS-C and KD could affect myocardial function in the acute phase (10, 11).

To assess the myocardial injury of MIS-C, speckle-tracking echocardiography (STE) with myocardial strain would be an ideal tool. Myocardial strain is a useful index of left ventricular deformation. The left ventricular global strain provides one of the best evidence on the diagnostic and prognostic implications for cardiac dysfunction (12). Some studies compared the myocardial strain using STE between MIS-C and KD (13, 14). Others compared the myocardial strain using STE between MIS-C and healthy children (15, 16). However, there was some inconsistency between the results, and sample sizes can affect the quality of evidence. In the scarcity of directly comparing studies, a network meta-analysis allows head-to-head comparisons indirectly through a common comparison group. Therefore, we conducted this network analysis to explore the myocardial strain of MIS-C.

The pre-registered protocol was implemented in the PROSPERO database (CRD42021264760). This manuscript was reported in accordance with PRISMA guideline (Supplementary Material).

Finally, nine case-control studies were included (Figure 1; 13–16, 20–24). Evaluation of the quality of involved studies is presented in Supplementary Table 2. These nine studies conducted between 2014 and 2021 involved 651 participants: 107 patients with MIS-C, 188 patients with KD, and 356 healthy children (Table 1). Geometry of the network is shown in Figure 2.

This is the first meta-analysis regarding the changes of myocardial strain in patients with MIS-C, compared with KD and healthy children. The results of this network meta-analysis revealed that MIS-C dEF group had lower LVEF, higher GLS and GCS than KD. MIS-C pEF group had similar LVEF, GLS, and GCS with KD. MIS-C pEF and KD had preserved LVEF, impaired GLS, and GCS in the acute phase before treatment compared with the healthy controls. In this study, GLS and GCS served as explicit indexes for MIS-C, which seems more sensitive than LVEF.

Kawasaki disease is a well-known, self-limited, systemic inflammatory vasculitis that mainly affects small- and medium-sized arteries. Several previous studies confirmed impaired left ventricular myocardial strain of KD in the acute phase using STE (20, 22) or velocity vector imaging (25, 26). Our results found that KD had impaired GLS and GCS in the acute phase compared with the healthy children, consistent with those published articles (20, 22, 25, 26). The progressive structural alterations of the myocardium and coronary arteries were confirmed during the convalescent phase of KD in the previous studies (27–29). Therefore, some studies suggested that patients with KD who had clinical recovered, need long-term follow-up to detect long-lasting impaired left ventricular myocardial strain using STE (30–33) or cardiac magnetic resonance (34).

The summarized course of myocardial strain change in patients with KD may help to better understand the recovery of MIS-C due to MIS-C having some overlapping features with KD. Before LVEF decreased or symptoms appeared, myocardial strain has emerged as a promising parameter of subclinical myocardial dysfunction (35). Myocardial strain can be measured via echocardiography/STE or cardiac magnetic resonance (36). However, it may be challenging to perform cardiac magnetic resonance in MIS-C because young children do not cooperate and their clinical instability (10). In order to assess the functional state of the left ventricle, STE is the most suitable technique for measuring myocardial strain (12).

Patient with MIS-C usually have fever, laboratory evidence of inflammation, and multisystem organ involvement (10). Although shares similarities with KD, MIS-C also has part features of myocarditis and toxic-shock syndrome (36). MIS-C and KD are distinct syndromes. Current evidence indicates that MIS-C is the result of an exaggerated innate and adaptive immune response, characterized by a cytokine storm, and that it is triggered by prior SARS-CoV-2 exposure (36).

The clinical course for MIS-C appears to be more severe during the acute phase. The death rate of MIS-C is 0.87% (52/5,973), compared with 0.17% of KD (4, 37). All the children who died from MIS-C had severe cardiovascular involvement (5). Recently, a study with 539 patients with MIS-C found that 65.8% of patients have preserved LVEF and 34.2% of patients have depressed LVEF (19). LVEF may become a source of heterogeneity of MIS-C studies. Therefore, as suggested by the previous research (17–19), we divided MIS-C into two subgroups. Meanwhile, we strengthened the evidence of left ventricular deformation of MIS-C by using network meta-analysis and found the difference between these two groups: left ventricular dysfunction of MIS-C dEF group was more severe than KD, but MIS-C pEF group was similar with KD in the acute phase.

Several studies focused on the recovery of MIS-C with follow-up for short-term (38, 39), mid-term (19, 40, 41), and 1-year using conventional echocardiography (42). In total, 91.0% of patients with MIS-C had a normal LVEF by 30 days (19). LVEF of all patients with MIS-C needed 74–90 days to return to normal (19, 42). However, cardiac magnetic resonance studies did not find any abnormality in patients with MIS-C after 27 ± 14 days (43), or a 2-month follow-up (44). In our involved study, three studies performed the short-term follow-up (13, 14, 16). After treatment, LVEF and GCS normalized by 7–9 days of illness, impaired GLS persisted in most of the patients with MIS-C (14, 16), similar findings were reported by a recent MIS-C cohort study (45). GLS may be a good follow-up index for MIS-C. Thus, we recommend long-term, regular intervals, follow-up with myocardial strain echocardiography for MIS-C, supplemented with cardiac magnetic resonance if clinical conditions permit.

Global longitudinal strain is usually associated with adverse outcomes, especially in patients with myocarditis (46), heart failure (47), or cardiomyopathy (48). GLS may be a clinical predictor for MIS-C. In patients with higher GLS, they have higher risk of intensive care, mechanical ventilation, or inotropic support (16, 18, 45). Meanwhile, they may stay longer in intensive care unit or hospital (18, 45). Meanwhile, correlations of GLS with laboratory parameters in patients with MIS-C were reported, such as C-reactive protein, troponin, and brain natriuretic peptide, indicating the presence of myocarditis and cardiac dysfunction (13, 16, 45, 49). Therefore, the impaired myocardial strain on the initial echocardiography of patients presenting with KD-like illness may be a clue to differential diagnosis. Such patients require closer clinical observation for the development of cardiac dysfunction (13).

MIS-C dEF was more severe than KD, both in LVEF and global myocardial strain. MIS-C pEF and KD were similar with mild-impaired left ventricular myocardial strain, compared with the healthy children. Global myocardial strain may be a monitoring index for MIS-C.

The original contributions presented in this study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.

KL contributed to the data collection, data analysis, and manuscript writing. JY contributed to the data collection and data analysis. GS contributed to the project development and manuscript writing. All authors contributed intellectually to the work and read and approved the final manuscript.

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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