Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the second most common form of the disease affecting about 40 to 50 percent of children with cardiomyopathy. Also known as hypertrophic obstructive cardiomyopathy (HOCM), idiopathic hypertrophic sub aortic stenosis (IHSS), asymmetrical septal hypertrophy (ASH) and non-obstructive hypertrophic cardiomyopathy (HCM), it occurs at a rate of five per million children according to the Pediatric Cardiomyopathy Registry. HCM can affect either gender and occur at any age. Among children, the average age of diagnosis is 7 years, and one third are diagnosed as infants (before age 1 year).

HCM refers to an abnormal growth and arrangement of muscle fibers in the heart (myocardial disarray), which thickens the heart walls. Excessive thickening of the heart muscle makes the heart’s chambers stiffer and smaller which affects the flow of blood in and out of the heart. HCM can eventually lead to obstruction of blood flow and a relaxation of the heart’s left ventricle.

Some children with HCM have an increased risk for arrhythmias and sudden cardiac arrest. In advanced cases, the disease may progress to dilated cardiomyopathy.

HCM is classified according to where the heart walls have thickened:

  • Asymmetric septal hypertrophy: thickening is in the left ventricle and septum separating the heart's chambers
  • Symmetric ventricular hypertrophy: thickening is evenly distributed throughout the ventricle, septum and wall
  • Apical hypertrophy: thickening occurs in the bottom portion of the heart.

Causes of Hypertrophic Cardiomyopathy

In the majority of cases, HCM is inherited. It is commonly found in more than one family member and across generations. HCM can also occur secondary to other genetic diseases. These include metabolic disorders, malformation syndromes, neuromuscular disorders, and glycogen-storage disorders. With metabolic disorders, there is problem with how the body breaks down food substances to generate energy for the heart. With mitochondrial disorders, the heart’s ability to utilize energy is diminished.

Restrictive Cardiomyopathy


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