Cardiomyopathies Part One, Hypertrophic
Cardiomyopathies in the neonate are diverse group diseases that are strictly defined as “a myocardial disorder in which the heart muscle is structurally and functionally abnormal, in the absence of coronary artery disease, hypertension, valvular disease, and congenital defects sufficient to cause the abnormality”.
There are four major types: hypertrophic, dilated, restrictive and arrhythmogenic right ventricular. There are other variants that are unclassified, but in some circumstances, differing types of cardiomyopathies can co-exist, such as hypertrophic and dilated types.
Most hypertrophic cardiomyopathies are genetic disorders with familial connections and can further be sub classified according to type, such as protein diseases (three fifths of this population) that are chromosomal disorders that affect the development of the myocardium. Examples of these would be sarcomeric protein diseases, glycogen and lysosomal storage diseases and disorders of fatty acid metabolism.
Syndromes such as Noonan’s, LEOPARD, and Friedreich’s ataxia are other variants. For example, Noonan’s and LEOPARD children are characterized by short stature, dysmorphic faces, skeletal abnormalities and webbed necks. In these children, pulmonary stenosis is a common finding.
These genetic types cause disarray and fibrosis of the myocardium. Systolic and diastolic dysfunction is a major consequence of hypertrophic diseases as well as LVOT obstruction and arrhythmias.
Most individuals are asymptomatic until they become adolescents; early n life they may present with cardiac failure, ECG abnormalities, shortness of breath and failure to thrive. In older children the most common symptoms are dyspnea and chest pain.
Myocarditis (or an inflammation of the myocardium) can play an important role in the development of this disease. Viruses are the most likely cause of myocarditis but it may also be bacterial, fungal, protozoa or parasitic, as well as an autoimmune response.
Look for left ventricular hypertrophy (LVH) and/or dilatation. The hypertrophy may be asymmetric so pay close attention to possible obstructions of the left ventricular outflow tract (LVOT). Diastolic function is assessed using the usual techniques such as tissue Doppler and/or strain gauge. Arrhythmias are common, especially with exertion; therefore stress testing is a useful diagnostic tool.
Treatment is typically prophylactic. In cases where there is significant obstruction of the LVOT, a surgical myectomy may be performed. The prevention of arrhythmias that could result in sudden death are an important aspect of treatment. Some patients may require an implantable defibrillator. Hypertrophic diseases are often familial; therefore other members of the family should be assessed if they are thought to be at risk.
Ken Heiden RDCS, RVT
Bibliography: “Paediatric Cardiology”, 3’d edition by Robert Anderson MD