Cardiomyopathy

Cardiomyopathy - Introduction

The cardiomyopathies constitute a group of acute or chronic myocardial diseases. They share certain general characteristics:

• High family incidence

• Cardiomegaly

• No or insignificant murmur

• No central cyanosis

• Normal or low blood pressure

• Dyspnea

• Arrhythmias

• 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 Cardiomyopathies

The primary cardiomyopathies are sub-grouped into three types according to structure and function:

• Dilated

• Hypertrophic

• Restrictive

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% were shown to have an intraventricular septum 30% or thicker than the 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 Cardiomyopathy

It 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.

Secondary Cardiomyopathies

Skeletal Myopathies:

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.

Mitochondrial Myopathies:

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 a short PR interval with increase ventricular voltages. Echocardiography shows progressive severe ventricular hypertrophy. The 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.

Mucopolysaccharidosis (MPS):

The mucopolysaccharidosis includes MPS I - Hurler's syndrome and MPS II- Hunter's syndrome. There is an 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.

Lipidosis:

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.

Cardiotoxins:

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 the myocardium.

Pediatric Systemic Diseases

Many pediatric systemic diseases like thyroid disorder, parathyroid disease, chronic anemia, malnutrition, beriberi, and selenium deficiency are associated with cardiomegaly.

Presentation

Dilated Cardiomyopthy (Congestive)

It is the commonest cardiomyopathy in children. Dilated cardiomyopathy is characterized by a reduction in the systolic function of the ventricles with increased dilatation of the chambers. The characteristic echocardiographic appearance is of dilatation of left or both ventricular cavities with reduced contractility. It presents as a newly diagnosed cardiac failure after infancy with tachycardia, tachypnea, pulmonary edema, and/or elevated jugular venous pressure depending upon left or right ventricular involvement. A gallop rhythm is common and a murmur of mitral regurgitation may be audible. The etiology remains undiscovered, a past attack of myocarditis is most commonly considered as a cause.

Hypertrophic Cardiomyopathy (HOCM)

Clinical presentation - Most children are referred for a systolic murmur and are asymptomatic. Breathlessness, ischaemic cardiac pain, and syncope are common in adolescence. Sudden death occurs in 15% of patients who are previously diagnosed.

Pulse is regular (maybe irregular if the patient is in atrial fibrillation) and of normal volume or often jerky (due to rapid ventricular ejection) in nature and JVP is not elevated. The cardiac apex is forceful and shows double impulse due to forceful presystolic impulse. An early systolic murmur with a thrill at the left lower sternal border conducted to the aortic area is audible. 25% of patients may have a systolic murmur due to mitral regurgitation.

Dilated Cardiomyopathy - Investigations

The cardiomyopathies constitute a group of acute or chronic myocardial diseases. They share certain general characteristics:

• X ray: Demonstrates cardiomegaly often with pulmonary edema.

• ECG: Broadening of QRS complex and evidence of ventricular strain with T wave changes. (Inverted 'T' waves in V5 & V6). A mild increase in left ventricular voltage. Exceptionally deep Q waves in lead III and V5 & V6.

• Echocardiography: Hypokinesia of left ventricle with diminished fractional shortening or ejection fraction.

Differential diagnosis

Acute myocarditis

Spontaneous improvement is common in both conditions and biopsy also is not conclusive in either case. So often, it is wiser to consider and manage patients of myocarditis similar to those as dilated cardiomyopathy.

Endocardial fibroelastosis

Aberrant left coronary artery:

Hypertrophic Cardiomyopathy (HOCM) - Investigations

• Chest X-ray may be normal in early stages but later on left ventricle is enlarged with prominent left atrium

• ECG: Left ventricular hypertrophy with abnormal q waves in V5 & V6 due to septal hypertrophy.

• Echocardiography: Gross thickening of interventricular septum. Mitral valve echo shows systolic anterior movement of mitral valve. Normal injection fraction

Dilated Cardiomyopathy - Treatment

• Fluid restriction initially

• Diuretics to reduce preload

• Intravenous ionotropes with vasodilators - Dobutamine is a common first choice drug. Digoxin may have positive ionotropic effect but its role remains unclear.

• Angiotensin converting enzyme inhibitors improves survival and left ventricular dysfunction. Once phase of circulatory failure is over, start with 0.1 mg/kg of captopril and it can be increased up to 1-2 mg/kg/24 hrs in divided doses.

• Anticoagulants are usually given to prevent intracavity thrombus formation.

• Antiarrhythmics should be used if patient is symptomatic but Antiarrhythmics are negative ionotropics so they have to be used with caution.

Dilated Cardiomyopathy - Prognosis

Although the majority of cases have a downhill course, a few especially presenting in infancy ultimately improve. It is the commonest reason for cardiac transplantation in children and actual survival after transplantation is 8% at 3 years.

Hypertrophic Cardiomyopathy (HOCM) - Treatment

No treatment is needed for asymptomatic children. Children with chest pain, syncope, and dyspnea should be treated with propranolol, which improves diastolic relaxation of the left ventricle. If no improvement is seen with medical treatment, surgical resection of hypertrophied include may help.

Prognosis - Though ultimately fatal in the majority, the interval between discovery to death often goes in decades. There have been great advances in the molecular genetics of HOCM. Restriction fragment length polymorphic markers have localized the gene to chromosome 14.