4. PATHOLOGY
The principal mechanism of cardiac involvement in viral
myocarditis is believed to be a cell-mediated
immunologic reaction, not merely myocardial damage
from viral replication.
Isolation of virus from the myocardium is unusual at
autopsy.
The inflamed myocardium is soft, flabby, and pale, with
areas of scarring on gross examination.
Microscopic examination reveals patchy infiltrations by
plasma cells, mononuclear leukocytes, and some
eosinophils during the acute phase and giant cell
infiltration in the later stages
5. CLINICAL FEATURES
Older children may have a history of an upper respiratory
infection
The illness may have a sudden onset in newborns and
small infants, with anorexia, vomiting, lethargy, and
occasionally circulatory shock
In neonates and infants, signs of CHF may be present;
these include poor heart tone, tachycardia, gallop rhythm,
tachypnea, and, rarely, cyanosis
In older children, a gradual onset of CHF and arrhythmia
are commonly seen.
Acute myocarditis is distinguished from fulminant
myocarditis, which is associated with an acute onset and
severe hemodynamic compromise
In some cases, myocarditis may be asymptomatic.
It may present with sudden unexpected death that is
presumably due to ventricular arrhythmia.
6. Cont…
Signs of respiratory distress due to congestion
S3 and occasionally S4 gallop
Quiet precordium
A soft, systolic heart murmur which are functional
Irregular rhythm caused by supraventricular or ventricular
ectopic beats may be audible.
In acute fulminant myocarditis, signs of low cardiac
output may be present, including hypotension, poor
pulses and perfusion, and altered mental status.
A pericardial friction rub and effusion may become
evident in some patients with myopericarditis.
Hepatomegaly may be present
7. LABS
ECG - low QRS voltages, ST-T changes, prolongation of
the QT interval, and arrhythmias, especially premature
contractions.
X-Ray -Cardiomegaly of varying degrees
Echo - Echo reveals cardiac chamber enlargement and
impaired left ventricle (LV) function, often regional in
nature
Radionuclide scanning (after administration of gallium-67
or technetium-99m pyrophosphate) may identify
inflammatory and necrotic changes characteristic of
myocarditis
8. LABS
Cardiac troponin levels (troponin-I and -T) and
myocardial enzymes (creatine kinase [CK], MB
isoenzyme of CK [CK-MB]) may be elevated.
In children, the normal value of cardiac troponin-I has
been reported to be 2 ng/mL or less, and it is frequently
below the level of detection for the assay.
Troponin levels may be more sensitive than the cardiac
enzymes.
Confirmation of myocarditis still requires endomyocardial
biopsy showing histological or immunohistological
evidence of inflammation
9. NATURAL HISTORY
The mortality rate is as high as 75% in symptomatic
neonates with acute viral myocarditis.
The majority of patients, especially those with mild
inflammation, recover completely.
Some patients develop subacute or chronic myocarditis
with persistent cardiomegaly with or without signs of CHF
and ECG evidence of left ventricular hypertrophy (LVH)
or combined ventricular hypertrophy (CVH).
Myocarditis may be a precursor to idiopathic dilated
cardiomyopathy.
10. MANAGEMENT
Bed rest and limitation in activities are recommended
during the acute phase (because exercise intensifies the
damage from myocarditis in experimental animals).
Treatment of heart failure with furosemide
Digoxin may be given cautiously, using half of the usual
digitalizing dose.
Arrhythmias should be treated aggressively and may
require the use of IV amiodarone.
Rapid-acting inotropic agents, such as dobutamine or
dopamine, are useful in critically ill children
11. PROGNOSIS
The prognosis of symptomatic acute myocarditis in
newborns is poor, and 75% mortality has been reported.
The prognosis is better for children and adolescents,
Recovery of ventricular function has been reported in 10-
50% of patients
Factors predictive of unremitting cardiac failure included;
1. ejection fraction <30 percent,
2. shortening fraction <15 percent,
3. left ventricular (LV) dilatation,
4. and moderate to severe mitral regurgitation at the time
of admission
