State-of-the-Art Pediatrics

Myocarditis: Getting to the Heart of the Matter

Author: David Sutcliffe, MD | Pediatric Heart Failure, VAD, and Transplant Cardiologist | Ward Family Heart Center | Assistant Professor of Pediatrics

Column Editor: Amita Amonker, MD, FAAP | Pediatric Hospitalist | Assistant Professor of Pediatrics, UMKC School of Medicine 

Generally, a child presenting with feeding intolerance or poor weight gain is suffering from reflux disease, milk protein allergy or gastroenteritis. Likewise, a teenager with exertional fatigue may have fallen prey to an excessive amount of screen time and inactivity. But in two out of 100,000 children, these symptoms will relate to one of the most common acquired heart diseases in pediatrics – myocarditis.¹

Myocarditis is an inflammatory condition of the cardiac muscle that causes injury and, potentially, the eventual development of scar tissue and chronic heart failure. Most frequently myocarditis is the result of a viral infection that initiates an inflammatory surge. The propagation of this inflammation is the result of an inappropriate and misguided immune response that targets the heart. Whether the result of a parvovirus or enterovirus infection, lupus, or even an mRNA vaccine, myocarditis represents 0.05% of U.S. hospitalizations.¹ Encountered symptoms coincide with the bimodal age distribution of patients, with <2-year-olds typically presenting with breathing difficulties and poor feeding, while >13-year-olds similarly experience dyspnea but with chest pain. Despite the varied symptoms that bring children with myocarditis to medical attention, the majority (60%) will have some degree of ventricular dysfunction at presentation. Not surprisingly, the severity of the illness often coincides with the degree of ventricular dysfunction at presentation ranging from a mild illness to fulminant myocarditis accompanied by signs of cardiogenic shock.²

The tools used for diagnosing myocarditis have evolved over the past 20 years. Initial studies should include a screening electrocardiogram to assess for ST segment changes or arrhythmias as well as troponin levels to assess for evidence of acute myocardial injury. In the setting of clear abnormalities shown with these screening studies, an echocardiogram can define the presence of associated ventricular dysfunction. Though there is no replacement for the tried-and-true ECG and echo for initial screening, there has been a shift away from the previous gold standard of catheter-based cardiac biopsy to one of cardiac MRI (CMR) in order to definitively diagnose myocarditis. Though challenges may be encountered when young or critically unstable children require anesthesia for such radiologic studies, CMR offers a less invasive alternative to biopsies, and can reliably show characteristic patterns of myocardial inflammation that persist beyond the acute presenting state with excellent test characteristics.

As this disease state is defined by a prominent inflammatory component, immunomodulators such as intravenous immunoglobulin (IVIG), corticosteroids and immunity-targeting monoclonal antibodies have historically been used as the foundation of management. Though uncommonly encountered entities such as giant cell myocarditis or lupus myocarditis will often show beneficial response to these therapies, classic viral-mediated myocarditis has failed to show such consistent benefits. A recent multicenter, retrospective study by Butts et al. showed no clinical benefit of IVIG, with those who received it showing a higher risk for progression to heart transplantation or death.² Though it was clear that those who received IVIG were a higher risk population, these findings exemplify the repeated phenomenon that an IVIG “rescue effect” is not seen. With a lack of curative options, treatment therefore focuses on supportive care during the acute phase of disease, an oral heart failure regimen to coax recovery in those with residual ventricular dysfunction, and the ageless therapeutic tincture of time. As such, all patients who develop myocarditis need an absolute exercise restriction for three to six months to allow continued healing and risk mitigation.

Although myocarditis has long been recognized as a disease entity, the COVID-19 pandemic era has brought about new entities in SARS-CoV-2 myocarditis as well as mRNA vaccine-related myocarditis. Though longitudinal data are lacking, SARS-CoV-2 is a rare but clear risk factor for developing myocarditis in the presence or absence of multisystem inflammatory syndrome in children (MIS-C), with a clinical profile similar to other myocarditis etiologies.³ Vaccine-related myocarditis, however, seems to be a distinct entity altogether. Recent data by Truong et al. characterize this entity as extremely rare (0.006% of administered vaccine doses) and typically presenting within one week of the second dose.⁴ Symptoms at presentation were predominantly chest pain with ST segment changes on ECG and troponin elevation. Ventricular function was normal in 80%, and in those patients with depressed function at presentation full recovery was universal. Longitudinal study will undoubtedly be required as we grapple with these new entities as a health care workforce.

Outcomes in myocarditis have long been thought to split in thirds among those who recover fully, those who recover with residual need for cardiac care, and those who progress to end-stage heart failure requiring heart transplantation or succumbing to death. More recent data as depicted in Butts’ study suggest much loftier outcomes with 87% transplant-free survival to discharge.² Efforts to improve these outcomes continue, through medical or mechanical circulatory support, by identifying safe and reliable treatment targets so we may be able to ensure that myocarditis is a fully reversible disease.

References: 

1. Tunuguntla H, Jeewa A, Denfield SW. Acute myocarditis and pericarditis in children. Pediatr Rev. 2019;40(1):14-25.
2. Butts RJ, Boyle GJ, Deshpande SR, et al. Characteristics of clinically diagnosed pediatric myocarditis in a contemporary multi-center cohort. Pediatr Cardiol. 2017;38(6):1175-1182.
3. Boehmer TK, Kompaniyets L, Lavery AM, et al. Association between COVID-19 and myocarditis using hospital-based administrative data – United States, March 2020–January 2021. MMWR Morb Mortal Wkly Rep. 2021;70:1228-1232.
4. Truong DT, Dionne A, Muniz JC, et al. Clinically suspected myocarditis temporally related to COVID-19 vaccination in adolescents and young adults. Circulation. 2022;145(5):345-356.