Hypertrophic Cardiomyopathy in Children

What is hypertrophic cardiomyopathy?

Hypertrophic cardiomyopathy (HCM) is an inherited disease that affects certain proteins within heart muscle cells. It passes from parent to child through the chromosomes. So far, about 100 different errors (mutations) in 10 genes that cause HCM have been found. It is quite common for a genetic disease, and affects about 1 in 500 people. Other terms used to describe the problem are hypertrophic obstructive cardiomyopathy (HOCM) and idiopathic hypertrophic subaortic stenosis (IHSS).

The normal heart is a four-chamber pump. The walls of the heart are made of layers of muscle cells. The heart rhythm is under the control of the heart’s electrical system.. Heart muscle cells respond to an electrical impulse by briskly contracting (shortening). When the cells contract together, this "squeezes" the chamber and blood is pumped forward. Between contractions, the cells relax (lengthen) allowing blood to fill the heart chambers for the next heartbeat. In HCM, the proteins within the muscle cells that allow the cell to contract and relax are abnormal. This results in stiff heart walls that do not relax in the normal way between heartbeats. The medical term for this is diastolic dysfunction.

In HCM, the muscle cells are also thick (the medical term for this is hypertrophy), causing the heart walls to be thick as well. This effect is seen most in the ventricular septum- the wall between the heart’s two lower chambers-the ventricles. In some cases, the wall becomes so thick that it obstructs the flow of blood out to the body. This can cause symptoms of chest pain during exercise and makes the person more prone to life-threatening abnormal heart rhythms such as ventricular tachycardia or ventricular fibrillation. Even when there is no blockage of blood flow, the heart’s thick walls can cause the person to tire easily.

How does this problem affect my child's health?

Although HCM is a serious problem, the health effects vary widely both in age of onset and severity. Often, there are mild or no symptoms until late childhood or the teen-age years. The most common symptom is low stamina with shortness of breath and chest pain during exercise. In some, during later adulthood, the heart’s chronic overwork causes heart enlargement and symptoms of congestive heart failure.

In people with HCM, there is an increased risk for abnormal heart rhythms such as Wolff-Parkinson-White syndrome, supraventricular tachycardia, atrial flutter and atrial fibrillation. There is also an increased risk for sudden cardiac death (caused by ventricular tachycardia or ventricular fibrillation), which may be higher in patients with very thick heart walls or severe blockage of blood flow from the left side of the heart. A "near-miss" sudden cardiac death (a life-threatening abnormal rhythm that self-converts) may appear to be a "fainting spell." In the future, advances in genetic testing may allow doctors to predict who is at higher risk for sudden death and to take preventive measures (for example, implanting cardioverter-defibrillator or ICD).

How is this problem diagnosed?

Symptoms: Possible symptoms include palpitations ("heart-racing" or "skipping heartbeat"), chest pain and shortness of breath with exertion, and fainting.

Physical findings: The exam is usually normal other than a heart murmur.

Medical tests: An echocardiogram is the main test used to make the diagnosis of hypertrophic cardiomyopathy. An electrocardiogram (ECG) is also done and is almost always abnormal. Other heart tests include a Holter monitor, and chest x-ray. Sometimes, a heart catheterization is done. If there are heart rhythm problems, an electrophysiologic study may be needed.

How is the problem treated?

Heart medicines such as calcium channel blockers (verapamil) and beta blockers (propanolol, atenolol) are used to promote heart muscle relaxation. Beta blockers also help prevent life-threatening abnormal heart rhythms (ventricular tachycardia). If life-threatening arrhythmias occur or the person is thought to be at high risk for such arrhythmias, an ICD may be needed. A heart operation, called a myomectomy, is sometimes done if there is a significant blockage of blood flow. In this operation, some of the excess heart muscle is removed. A heart transplant may be needed if there are severe symptoms in spite of treatment with heart medicines/myomectomy. A heart transplant may also be needed if there are abnormal heart rhythms that cannot be safely treated by a cardioverter-defibrillator.

What are the long-term health issues for these children?

While HCM can be a serious problem, many people have only mild disease that causes mild or no symptoms. The course of the disease, severity and health effects vary widely, even among family members. Overall, the risk of serious problems is quite low as long as the hypertrophy (thickening of heart muscle wall) remains mild. In more severe cases, treatment with high-dose beta blockers and ICD implantation (if life-threatening arrhythmias) has greatly improved treatment outcomes.

SBE prophylaxis: Children with HCM are at increased risk for subacute bacterial endocarditis (SBE). This is an infection of the heart caused by bacteria in the blood stream. Children with heart defects are more prone to this problem because of the altered flow of blood through the heart and/or abnormal heart valves. SBE is can occur after dental work or medical procedures on the GI or respiratory tract because these procedures almost always result in some bacteria entering the blood. SBE can usually be prevented by taking an antibiotic before these procedures.

Exercise guidelines: An individual exercise program is best planned with the doctor so that all factors can be included. Most children with HCM are not allowed to play competitive sports but are allowed to play low-impact recreational sports. It is important for the children to always be able to self-limit their activity, that is, to rest whenever they feel the need to do so. Children with HCM usually do not participate in vigorous gym class routines, but if light exercise is permitted by their doctor, they should be allowed to self-limit their level of exertion and they should not be graded (which could pressure them to exceed their natural limits).

References

Gajarski RJ & Towbin J. Recent advances in the etiology, diagnosis, and treatment of myocarditis and cardiomyopathies in children. Curr Opinion Pediatrics 1995;7:587-594.

Spirito et al. Magnitude of left ventricular hypertrophy and risk of sudden death in hypertrophic cadiomyopathy. New England J Med 2000;342:1778-1785.

Written by: S. LeRoy RN, MSN, CPNP

Reviewed September, 2012