Understanding the interconnectedness of heart and gut health in pediatric congenital heart disease and cardiomyopathy. Explore gastrointestinal symptoms like feeding dysfunction and postoperative issues.

Published: July 9, 2025

Myocarditis represents a significant cause of morbidity and mortality in pediatric patients, yet its clinical presentation can be deceptively subtle. As inflammation of the heart muscle and conduction system, myocarditis affects the heart’s ability to contract effectively and maintain normal rhythm, potentially leading to sudden cardiac death even in previously healthy children.

Epidemiology and risk factors

Cardiomyopathy affects approximately 1 to 1.5 per 100,000 children annually in the United States, with myocarditis accounting for roughly 16% of identifiable causes of dilated cardiomyopathy. Several demographic patterns emerge:

• Age: Incidence is significantly higher in infants under 1 year (4 to 8 per 100,000).
• Gender: Boys are more commonly affected than girls.
• Race: African American children show higher incidence rates compared with white children.
• Seasonal variation: Viral patterns influence annual trends, with enterovirus and influenza being common culprits.

Etiology and pathophysiology

While any virus can trigger myocarditis, the most common causes include:

Historical viral patterns:

• Earlier era: Adenovirus, enterovirus
• Recent decades: Parvovirus, human herpesvirus 6 (HHV-6)
• Current era: COVID-19 and associated multisystem inflammatory syndrome in children (MIS-C)

Noninfectious causes include autoimmune diseases (particularly lupus), hypersensitivity reactions, medications and toxins, though viral etiologies predominate.

The pathophysiology involves direct viral invasion and subsequent immune-mediated damage to myocardial tissue. This can occur during acute viral illness or in a postviral phase weeks after initial infection.

Clinical presentation: The diagnostic challenge

Perhaps the most critical clinical pearl is recognizing that gastrointestinal (GI) symptoms are the most common presenting complaint in pediatric heart failure, including myocarditis-induced cardiomyopathy. Studies consistently show that nausea, vomiting, abdominal pain and feeding intolerance are more common than classic dyspnea or chest pain.

Key clinical insight: More than half of pediatric heart failure cases are initially misdiagnosed, often as viral gastroenteritis. Consider cardiac etiology in children with:

• Recurrent GI complaints
• Parental concern that “something isn’t right”
• Abdominal pain in adolescents
• Feeding intolerance in infants

Spectrum of presentation

Myocarditis presentations range from:

• Subclinical: Asymptomatic with only biomarker or imaging abnormalities
• Acute symptomatic: upper respiratory infection symptoms, chest pain, palpitations, syncope
• Heart failure: Exercise intolerance, tachypnea, GI symptoms
• Cardiac arrest: Sudden collapse (recognized cause of sudden cardiac death)

Diagnostic approach

Modern diagnosis relies on clinical criteria rather than invasive biopsy:

Definite myocarditis: Positive endomyocardial biopsy

Probable myocarditis (acute or subclinical): Requires one or more of:

1. Elevated cardiac biomarkers (primarily troponin)
2. Electrocardiogram (EKG) changes suggestive of cardiac injury
3. Echocardiogram or MRI evidence of ventricular dysfunction

Diagnostic modalities

Laboratory testing:

• Troponin (primary biomarker)
• Brain natriuretic peptide (supportive)
• Inflammatory markers (C-reactive protein; erythrocyte sedimentation rate — less specific)
• Viral studies when indicated

Electrocardiography:

• May show subtle changes (T-wave inversions, repolarization abnormalities)
• Can demonstrate dramatic ST elevations in severe cases
• Rhythm abnormalities may be present

Imaging:

• Chest X-ray: Often abnormal in symptomatic patients (cardiomegaly, pleural effusions)
• Echocardiography: To assess ventricular function and size
• Cardiac MRI: Gold standard for tissue characterization, showing edema, hyperemia and late gadolinium enhancement, indicating fibrosis

Biopsy considerations:

• Invasive with potential complications
• High false-negative rate
• Reserved for specific clinical scenarios
• Positive results are definitive, but negative results don’t exclude diagnosis.

Management strategies

Acute phase

Hospitalization is standard for suspected myocarditis due to unpredictable clinical course and potential for rapid deterioration.

Immunomodulatory therapy:

• Intravenous immunoglobulin: Often used for patients with ventricular dysfunction
• Corticosteroids: Considered for rhythm disturbances
• Evidence mixed for both therapies

Supportive care:

• Heart failure management (inotropes acutely, then oral agents)
• ACE inhibitors, aldosterone antagonists, beta-blockers
• Antiarrhythmic medications as needed
• Extracorporeal membrane oxygenation (ECMO) capability essential for severe cases

Monitoring and prognosis

Hospital course: Monitor until troponin trending down, ventricular function stable and arrhythmia burden controlled.

Key prognostic insight: Troponin levels don’t reliably predict severity. Patients with minimally elevated troponin can deteriorate rapidly, while those with very high levels may have preserved function.

Ventricular function patterns:

• Normal-sized ventricles with dysfunction: Often recover quickly, even after ECMO
• Dilated ventricles: May indicate longer disease duration and slower recovery

Management

Goal-directed medical therapy (ACE inhibitors, aldosterone antagonists, beta-blockers) should continue for one year after normalization of cardiac function. The timeline begins when echocardiogram normalizes, not from initial diagnosis.

Long-term outcomes

Three-year follow-up studies reveal:

• Persistent echo abnormalities in 40% to 45%
• Mortality rate 6% to 7%
• Heart transplant required in 15% to 20%
• Recovery of most patients, including some initially listed for transplant

Conclusion

Pediatric myocarditis remains a diagnostic and management challenge requiring high clinical suspicion, particularly in children presenting with GI symptoms. Early recognition, appropriate supportive care and adherence to activity restrictions can significantly improve outcomes. The key to successful management lies in maintaining clinical vigilance, understanding the disease’s unpredictable nature and providing comprehensive, long-term follow-up care.

Health care providers must remember that myocarditis can present as a great mimicker, and maintaining a low threshold for cardiac evaluation in children with unexplained symptoms may be lifesaving. The combination of clinical acumen, appropriate diagnostic testing and evidence-based management strategies offers the best outcomes for these vulnerable patients.