Understanding Hypertrophic Cardiomyopathy

What is hypertrophic cardiomyopathy?

Hypertrophic cardiomyopathy (HCM) is the second most common form of heart muscle disease, affecting about 40-50% of children with cardiomyopathy. "Hypertrophic" refers to the abnormal growth of muscle fibers in the heart. With HCM, the pumping function is normal but the heart muscle is thickened and stiff, making it difficult for the heart to relax and for blood to fill the heart chambers. The limited filling also prevents the heart from supplying enough blood to the body, especially during exercise. HCM usually affects the heart's main pumping chamber (left ventricle) with thickening of the septum, the muscle wall that separates the two lower chambers of the heart. Muscle thickening can occur throughout the heart or be worse in specific sections of the heart. This is referred to as asymmetric septal hypertrophy (septum is thicker than the rest of the wall), concentric hypertrophy (evenly distributed thickening of the entire ventricle) or apical hypertrophy (localized thickening at the tip of the heart).

With hypertrophic obstructive cardiomyopathy (HOCM), also known as idiopathic hypertrophic subaortic stenosis (IHSS), the muscle thickening restricts the blood flow out of the heart. Often, leakage of the mitral valve causes the blood in the lower chamber (left ventricle) to leak back into the upper chamber (left atrium).


How many children are affected?

HCM affects up to 500,000 people in the U.S. , with children under 12 years accounting for less than 10% of all cases. According to the Pediatric Cardiomyopathy Registry, HCM occurs at a rate of 5 per million children and is most often diagnosed during infancy and adolescence.

What causes hypertrophic cardiomyopathy?

The most common cause of HCM in children is a familial inherited disease affecting only the heart, followed by disorders that affect the entire body due to metabolic irregularities (fatty acid oxidation disorders, Pompe, mitochondrial defects). Other possible causes include genetic malformation syndromes (Noonan syndrome) and neuromuscular disorders (Friedreich's ataxia).

Genetic defects are a leading cause of HCM. Gene defects can be familial and it is estimated that 50-60% of children with HCM have a relative with the disease, although they may not be diagnosed or have symptoms. To date, 12 genes with 150 different genetic mutations have been identified to cause the familial form of HCM in adults. Most of the familial inherited cases are caused by sarcomeric mutations that affect the proteins responsible for the contraction of the heart muscle. Mutations are changes in the DNA of a gene that can be either inherited or occur "spontaneously" for unknown reasons during fetal development. The impact of these genetic mutations differs, which ex-plains why the severity of the disease varies widely among family members having the same condition. Familial HCM is usually inherited in an autosomal dominant manner in which one parent contributes the defective gene and the chance that a son or daughter will inherit the condition is 50%.

Children may have HCM associated with another genetic or metabolic disorder. In these cases, there is increased wall thickness because gene defects cause the abnormal accumulation of fat or sugars (glycogen) in the heart. Other gene defects can cause abnormalities in the mitochondria to produce this effect. These rare disorders are usually inherited in an autosomal recessive manner in which both parents contribute a defective gene and the chance that a son or daughter will inherit the condition is 25%.

What are the common symptoms?

There is tremendous variation in how the disease presents and progresses. Children under one year often present with symptoms of congestive heart failure, whereas older children may show no or mild symptoms. The onset of symptoms often coincides with the rapid growth and development of late childhood and early adolescence. The strenuous exercise of competitive sports has also been known to make symptoms of HCM more apparent.

Disease severity and symptoms are related to the extent and location of the hypertrophy and whether there is obstruction or mitral regurgitation. Children with HCM may experience shortness of breath (dyspnea), chest pain (angina), light-headedness or dizziness (presyncope), fainting (syncope), difficulty exercising or irregular heartbeats (palpitations). Symptoms in infants are more difficult to detect but include difficulty breathing, slow weight gain, excessive sweating (diaphoresis) and/or agitation during feeding due to chest pain. Children with severe HCM may have symptoms of heart failure such as difficulty breathing, fatigue, a persistent cough, abdominal pain, vomiting and/or swelling around the eyes and legs (edema).

Some children may develop abnormal heart rhythms (arrhythmia) where the heart beats too slow (bradycardia) or too fast (tachycardia). Symptoms include feeling strange or fast heartbeats (palpitations), fainting (syncope) and/or convulsions (seizures). These symptoms may appear at any stage of the disease even without a child having congestive heart failure or obvious symptoms of HCM.


How do you diagnose hypertrophic cardiomyopathy?

HCM may be diagnosed in a physical examination when a heart murmur is detected, although this is often absent in non-obstructive HCM. To diagnose HCM, physicians rely on noninvasive cardiac tests such as the echocardiogram with Doppler ultrasound and the electrocardiogram (EKG). A diagnosis of HCM is confirmed with an echo-cardiogram, which indicates the extent and location of the muscle thickness, how well the heart is pumping and the presence and severity of obstruction and mitral regurgitation. From this test, the velocity (the speed at which blood flows into the heart) and the ejection fraction (the percentage of blood ejected from the heart with each beat) can be calculated. A reduced velocity and higher than normal ejection fraction of 70-90% indicates HCM. An EKG provides information on the heart's electrical activity, abnormal heart rhythms and heart size. This test nearly always shows higher than normal voltages associated with thickened pumping chambers.

Other tests may be ordered to help determine a child's medical management and prognosis. These include an exercise stress test to see how well the heart can respond to exercise, a Holter monitor to look for abnormal heartbeats and magnetic resonance imaging (MRI) to measure the degree of muscle thickness and to evaluate heart and blood vessel function.

In some cases, more invasive cardiac tests may be needed. A cardiac catheterization may be performed to evaluate the degree of obstruction and the need for a heart transplant. Because HCM can cause potentially fatal arrhythmias, an electrophysiology (EP) study may be performed at the same time. During the EP test, a physician will try to provoke a fast heart rhythm (ventricular tachycardia) to determine whether anti-arrhythmic medication or an automatic implantable cardioverter defibrillator (AICD) will be necessary.

What are the treatment options?

For children with HCM, medical therapy aims to control symptoms related to heart obstruction, improve filling of the heart chambers and prevent arrhythmias. With optimal treatment, symptoms can be improved or eliminated in many children with HCM.

Several types of drugs are commonly used to control HCM in children. Beta-blockers (atenolol, metoprolol, propranolol) and/or calcium channel blockers (verapamil) may be prescribed to patients with obstructive HCM to reduce the heart's workload by slowing the heart rate and decreasing the force and contraction of the heart muscle. Diuretics (furosemide, spironolactone) help to reduce excess fluid in the body and may be prescribed in advanced stages of heart failure. For children with heart rhythm problems, anti-arrhythmic medications (amiodarone, digoxin, disopyramide, procaineamide, verapamil) may be prescribed to keep the heart beating at a regular rate. An anti-coagulant (aspirin, dipyridamole, enoxaparin, heparin, warfarin) may also be used to reduce the risk of stroke associated with HCM and atrial fibrillation.

A pacemaker or automatic implantable cardioverter defibrillator (AICD) may be inserted surgically to control arrhythmias that do not respond to medication. An AICD may be used to automatically correct life-threatening arrhythmias (atrial fibrillation or ventricular tachycardia) that may interfere with the heart's pumping ability and lead to sudden cardiac arrest. A child who has experienced a cardiac arrest, has a family history of sudden death or shows signs of severe arrhythmia would be a candidate for an AICD. A pacemaker may be recommended for patients with HOCM to reduce the severity of obstruction.

In patients with severe obstruction or mitral regurgitation, surgery may be recommended to control chest pain or symptoms of heart failure. During a septal myectomy, excess heart muscle is removed to relieve obstruction and, if necessary, a leaky mitral valve is repaired or replaced.


What is the prognosis?

The outcome of HCM is highly variable, with some children remaining asymptomatic, some developing symptoms and all remaining at risk for progressive heart failure and sudden death. In less than 10% of patients, the disease may progress to a point where the heart muscle thins and stretches (dilates) and the pumping performance deteriorates. However, a heart transplant is less common for children with HCM and is only recommended when there is severe, unmanageable heart failure.


What is the Children’s Cardiomyopathy Foundation?

The Children’s Cardiomyopathy Foundation (CCF) is a national non-profit organization dedicated to finding causes and cures for pediatric cardiomyopathy through the support of research, education, awareness and advocacy.

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Contact Information:

Children’s Cardiomyopathy Foundation

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Tel: 201-227-8852 | Fax: 201-227-7016
Toll Free: 866-808-CURE (2873)

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