Paediatrics chapters
Myocarditis
Inflammation of the heart muscle in children, usually after a viral infection: how it presents at different ages, the ECG, echo and MRI findings, supportive and specific treatment, and the long-term risk of dilated cardiomyopathy.
- Myocarditis is inflammation and necrosis of heart muscle, most often from viruses (coxsackie B, adenovirus, other enteroviruses); in Pakistan diphtheria remains an important toxic cause.
- Suspect it when a child with a recent viral illness has tachycardia out of proportion to fever, a gallop, muffled heart sounds, heart failure, arrhythmia or shock; the ECG shows low-voltage QRS with ST-T changes, echo shows a poorly contracting dilated heart, and cardiac MRI or biopsy confirms.
- Treatment is supportive (oxygen, diuretics, cautious inotropes, half-dose digoxin, amiodarone for arrhythmia, ECMO or transplant if refractory) with IVIG in selected cases; survivors need follow-up for dilated cardiomyopathy.
On this page
Overview
Myocarditis is inflammation of the heart muscle, with inflammatory cell infiltrate, myocyte necrosis and later fibrosis. In pure myocarditis the endocardium and pericardium are spared, although pericarditis can coexist (myopericarditis).
It can range from a mild, silent illness to fulminant heart failure, cardiogenic shock, arrhythmia and sudden death. It is an important cause of new heart failure in a previously healthy child and of dilated cardiomyopathy later.
Causes
| Group | Examples |
|---|---|
| Viral (commonest) | Coxsackievirus B, adenovirus, other enteroviruses (echovirus); also mumps, Epstein-Barr virus, influenza, parainfluenza, measles, varicella, HIV |
| Bacterial / toxin | Diphtheria (toxic myocarditis), Mycoplasma, meningococcal disease, leptospirosis, Lyme disease |
| Other infections | Rickettsial (Coxiella, Rocky Mountain spotted fever); parasitic: Chagas disease, Toxoplasma |
| Immune / connective tissue | Rheumatic fever, SLE, scleroderma, dermatomyositis, Kawasaki disease |
| Toxic / drugs | Doxorubicin, irradiation, cocaine, amphetamines, iron overload |
| Granulomatous / idiopathic | Sarcoid, idiopathic |
Viruses, mainly coxsackievirus B and adenovirus, cause most myocarditis in children.
Diphtheritic myocarditis (important in Pakistan)
- The toxin damages heart muscle; myocarditis can appear from 2 to 40 days after onset of the throat illness, most often in the second to sixth week, with circulatory failure typically in the second week.
- Rapid thready pulse, faint heart sounds, enlarged liver, heart failure; tachycardia out of proportion to fever.
- ECG: prolonged PR, ST and T-wave changes, any degree of heart block, including complete block.
- Toxic myocarditis causes about half or more of diphtheria deaths (Akbar gives 50-60%).
- Children with diphtheria need strict bed rest for 2-3 weeks and serial ECGs 2-3 times a week for 4-6 weeks.
Pathophysiology in brief
- Acute viral myocarditis can set off a fulminant inflammatory process: cellular infiltrates, cell degeneration and necrosis, then fibrosis.
- Where damage persists, the ventricles dilate and the child may be left with dilated cardiomyopathy.
The weakened, dilated ventricle stretches the mitral ring, causing mitral regurgitation.
Clinical features
The picture depends on age and on whether the illness is acute or chronic.
Neonates and infants
- Often fulminant: fever, severe heart failure, breathing difficulty, cyanosis.
- Distant (muffled) heart sounds, weak pulses, gallop rhythm.
- Tachycardia out of proportion to fever.
- Mitral regurgitation murmur from annular dilatation.
- Acidosis and shock; may mimic sepsis.
Older children
- Often a recent viral illness.
- Acute congestive heart failure: breathlessness, easy fatigue, tachycardia, gallop, hepatomegaly.
- Or a sudden onset of ventricular arrhythmia.
An infant with myocarditis may present simply with fast breathing (Akbar's case: a 2-week-old with respiratory distress). Cardiomegaly on the chest X-ray, a gallop, distant heart sounds and tachycardia out of proportion to fever point to the heart.
Investigations
| Test | Finding |
|---|---|
| ECG | Sinus tachycardia; low-voltage QRS complexes; ST-segment and T-wave changes; atrial or ventricular arrhythmias, heart block |
| Chest X-ray | Cardiomegaly, prominent pulmonary vessels, pulmonary oedema, pleural effusions (in severe cases) |
| Echocardiography | Poor ventricular function, dilated ventricles and left atrium, mitral regurgitation, often a pericardial effusion; excludes structural heart disease and an anomalous left coronary artery |
| Heart enzymes | Creatine phosphokinase and lactate dehydrogenase raised |
| BNP | Raised |
| ESR | Raised |
| Virology | Serum viral titres may be positive; PCR identifies viral RNA or DNA |
| Cardiac MRI | A standard imaging test for the diagnosis (Akbar) |
| Endomyocardial biopsy | Confirms inflammation and necrosis; done at cardiac catheterisation; also detects storage and mitochondrial disease; not without risk |
ECG low-voltage QRS with ST-T changes in a child with heart failure suggests myocarditis or pericarditis.
Differential diagnosis
- Idiopathic dilated cardiomyopathy.
- Anomalous origin of the left coronary artery.
- Endocardial fibroelastosis.
- Pericarditis.
- Metabolic: carnitine deficiency, hereditary mitochondrial defects.
Management
Supportive (the mainstay)
- Supportive measures for severe congestive heart failure or cardiogenic shock.
- Diuretics and afterload reduction (Nelson's supportive care for cardiomyopathy).
- Inotropes: dopamine, adrenaline (epinephrine) and milrinone support poor output and low perfusion.
- All inotropes, including digoxin, are used with caution because the inflamed myocardium is prone to arrhythmia; if digoxin is given, use half the usual dose.
- Arrhythmias: treat aggressively with IV amiodarone.
- Pericardiocentesis for tamponade.
- ECMO for infants and children in cardiogenic shock.
- Heart transplantation is the treatment of choice for refractory heart failure.
Specific / immunomodulatory
- Intravenous immunoglobulin (IVIG) 2 g/kg has been used, especially in acute viral myocarditis.
- Prednisone (2 mg/kg/day, tapered to 0.3 mg/kg/day over about 3 months): Akbar states it reduces myocardial inflammation and improves cardiac function.
- Diphtheria: prompt diphtheria antitoxin (within 48 hours) and penicillin or erythromycin, with bed rest for 2-3 weeks, since activity can worsen the myocarditis.
Digoxin at full dose in myocarditis can provoke dangerous arrhythmias. Use it carefully at reduced dose, or not at all.
Complications
- Cardiogenic shock and death in the acute phase.
- Arrhythmias, including heart block, and sudden death.
- Chronic dilated cardiomyopathy with long-term heart failure.
Prognosis and long-term follow-up
- Symptomatic neonates with acute viral myocarditis do poorly.
- Older children and those with milder illness do better; complete recovery is common.
- Children who progress to chronic dilated cardiomyopathy have a poor outlook without treatment.
Follow-up:
- Close monitoring and follow-up are essential once heart muscle disease is present (Nelson).
- Echocardiography tracks ventricular size and function.
- Continue heart failure treatment if function stays reduced; because cardiomyopathy carries a high mortality, transplantation is considered if it worsens.
- DPT immunisation (part of EPI) prevents diphtheria.
Expect: viral causes (coxsackie B, adenovirus) as the commonest; diphtheritic myocarditis timing and heart block in Pakistan; tachycardia out of proportion to fever, gallop and distant heart sounds; fulminant failure and shock in neonates; ECG low-voltage QRS with ST-T changes; echo poor function with dilated chambers and mitral regurgitation; raised heart enzymes and BNP; cardiac MRI as a standard imaging test and endomyocardial biopsy as confirmation; cautious use of inotropes and half-dose digoxin; amiodarone for arrhythmias; IVIG 2 g/kg; ECMO and transplant for refractory cases; dilated cardiomyopathy as the long-term complication.
Quick revision
- Myocarditis = inflammation and necrosis of heart muscle; viral (coxsackie B, adenovirus) commonest.
- Diphtheria: toxic myocarditis, usually in the second week; heart block; strict bed rest and serial ECGs.
- Clue: tachycardia out of proportion to fever, gallop, soft heart sounds, heart failure after a viral illness.
- ECG: low voltage, ST-T changes, arrhythmia. Echo: dilated poorly contracting ventricles, MR, effusion.
- Cardiac MRI non-invasive; endomyocardial biopsy confirms.
- Supportive care; inotropes with caution; digoxin at half dose; amiodarone; IVIG 2 g/kg; ECMO/transplant.
- Neonates worst outcome; risk of dilated cardiomyopathy.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).
FAQ
What is the most useful bedside clue to myocarditis in a febrile child?
A heart rate that stays high out of proportion to the fever, especially with a gallop rhythm, soft heart sounds or signs of heart failure.
Why is digoxin used cautiously in myocarditis?
The inflamed heart muscle is very sensitive to digoxin and prone to arrhythmia, so it is given, if at all, at about half the normal dose.
How is myocarditis confirmed?
Cardiac MRI is a standard non-invasive imaging test, and endomyocardial biopsy at catheterisation gives tissue proof, though it carries risk.
What happens to children who survive myocarditis?
Many recover fully, but some develop chronic dilated cardiomyopathy and need long-term heart failure care and follow-up with echocardiography.