cardiomyopathies constitute a group of acute or chronic myocardial diseases. They share certain general characteristics:
- High family incidence
- No or insignificant murmur
- No central cyanosis
- Normal or low blood pressure
- Intracardiac thrombosis or emboli
- Sudden death
The cardiomyopathies may be primary (idiopathic) or secondary (where the cause is known). An important part of the management of childhood cardiomyopathies involves search for a primary cause.
PRIMARY CARDIOMYOPATHIESThe primary cardiomyopathies are sub-grouped into
three types according to structure and function:
HYPERTROPHIC CARDIOMYOPATHY (HOCM)Hypertrophic obstructive cardiomyopathy is a disease of children, adolescents and young adults. It is based on the diagnosis of unexplained ventricular hypertrophy. It is now known that the condition is passed on with Mendelian dominant form of inheritance with incomplete penetrance. It is suggested by the finding in relatives of patients with HOCM, in which 50% of were shown to have an intraventricular septum 30% or more thick than left ventricular free wall. Theories included hamartomatous outgrowth of muscle, increased sensitivity to sympathetic stimulation and abnormal distribution of muscle bundles increasing the work of the ventricle producing secondary hypertrophy.
RESTRICTIVE CARDIOMYOPATHYIt is rare in children. In restrictive cardiomyopathy, ventricular compliance is reduced without ventricular hypertrophy and normal systolic function.
It is more commonly seen in adults due to sarcoidosis, amyloidosis and Fabry's disease, which are rarely seen in children.
Muscular dystrophies: Duchenne's and Becker's muscular dystrophy affect the myocardium also. Initially there is hypertrophy followed by progressive dilated cardiomyopathy.
Barth's syndrome, an X-linked condition involving skeletal musculature, intermittent neutropenia and abnormal mitochondria also cause cardiomyopathy.
Limb girdle muscular dystrophy may be associated with atrial arrhythmias.
A variety of enzyme deficiencies in the mitochondria are associated with skeletal features and cardiomyopathy. Carnitine is required to transport long chain fatty acids across the mitochondrial membrane and Acetyl CoA dehydrogenase is required for b oxidation of fatty acids in the mitochondria. So primary carnitine deficiency, Acyl CoA dehydrogenase deficiency, Cytochrome C oxidase deficiency are responsible. The cardiomyopathy is usually hypertrophic, occasionally dilated with reduced systolic function. When cardiomyopathy is due to primary carnitine deficiency, it responds to carnitine.
GLYCOGEN STORAGE DISEASE (GSD):
GSD - II A is an autosomal recessive acid maltase deficiency. With Type II A i.e. Pompe's disease there is glycogen deposition in the heart, skeletal muscle and liver. Clinically it presents with muscular weakness and hepatomegaly. The ECG shows short PR interval with increase ventricular voltages. Echocardiography shows progressive severe ventricular hypertrophy. Blood smear shows vacuolated lymphocytes.
GSD III also is known to cause hypertrophic cardiomyopathy in early adult life while
GSD IV causes dilated cardiomyopathy presenting in infancy with heart failure.
The mucopolysaccharidosis include MPS I - Hurler's syndrome and MPS II- Hunter's syndrome. There is accumulation of mucopolysaccharide in the mitral & aortic valves leading to regurgitation and heart failure. Initially, it leads to hypertrophic cardiomyopathy when there is heart failure it shows dilated cardiomyopathy.
Cardiac involvement has been reported in lipid storage diseases. Gaucher's disease is associated with restrictive cardiomyopathy. Both gangliosidoses GM1 and GM2 may be associated with myocardial hypertrophy/dilatation.
The iron storage disorder (hemochromatosis), copper storage (Wilson's disease) are associated with cardiomyopathies. In pediatric practice, anti-malignant drugs- anthracyclines, cyclophosphamide, mediastinal irradiation are known to cause damage to myocardium.
PEDIATRIC SYSTEMIC DISEASES
Many pediatric systemic diseases like thyroid disorder, parathyroid disease, chronic anemia, malnutrition, beriberi and selenium deficiency are associated with cardiomegaly.