Pediatric Cardiomyopathy
Hypertrophic Cardiomyopathy (HCM)

What is Hypertrophic Cardiomyopathy (HCM)?

Hypertrophic cardiomyopathy (HCM) is a condition of heart muscle disease in which the muscle is thickened (hypertrophic). This thickening typically occurs in the lower left chamber of the heart, called the left ventricle. Thickening of the heart muscle can occur at the septum (muscular wall that separates the left and right side of the heart), the posterior wall or free wall (outside wall of the left ventricle), the apex (the bottom of the heart) or throughout the entire left ventricle. When the muscle becomes thickened, it may make it difficult for an efficient amount of blood to flow into and out of the heart, especially during exercise. In some cases, the thickening of the muscle can block blood flow from the left ventricle to the aorta. This is called “outflow tract obstruction.

The cardiomyocytes (heart muscle cells) in individuals with HCM have characteristic features. Under a microscope, the cells appear disorganized and irregular (myocyte disarray). This disarray may cause changes in the electrical signals traveling through the lower chambers of the heart and lead to ventricular arrhythmias (abnormal heart rhythm). Hypertrophic cardiomyopathy affects an estimated 600,000 to 1.5 million Americans, or one in 500 people.

Hypertrophic Cardiomyopathy illustration.

Many individuals with HCM experience no symptoms. For those who have heart failure or ventricular arrhythmias, symptoms can include:

Older children and adults  

Newborns and babies  

  • Excessive sweating
  • Difficulty feeding or poor growth

Even though some people can have HCM and experience no symptoms, they may still be at risk for complications of the condition. The most serious complication of HCM is sudden cardiac arrest. Sudden cardiac arrest is a sudden loss of heart function caused by a dangerously fast heart rhythm called ventricular tachycardia. Unless emergency treatments, including CPR and defibrillation, are initiated immediately, sudden cardiac death can occur. Most people with HCM have a low risk for sudden cardiac death. However, HCM is the most common cause of sudden cardiac death in people under age 30. For this reason, it is important for anyone at risk to be followed by a cardiologist with experience in caring for individuals with HCM.

HCM is largely a genetic condition. When an individual is diagnosed with HCM, there is a 40 to 70 percent chance that an underlying genetic cause will be identified. Most commonly, the genetic cause results in a condition that runs in a family and affects only the heart. It is possible that parents, siblings, and even aunts/uncles or cousins of an individual diagnosed with HCM may also have this heart muscle condition. If they haven’t had cardiac screening, family members may not know they are affected. There are other genetic causes of HCM which can be associated with other health problems. These include genetic syndromes, metabolic, and mitochondrial disorders.

Hypertrophy can be acquired and is not always genetic. For example, hypertrophy can result from high blood pressure that has gone untreated or poorly controlled for a period of time. Individuals who are endurance athletes can also develop hypertrophy. In some people, the cause of HCM is unknown.

The diagnosis of HCM is based on family history, medical history, physical exam,and cardiac testing.

  • Family history: A family tree should be constructed with specific attention cardiomyopathy, rhythm problems, sudden cardiac or unexplained death, cardiac surgery or presence of other cardiac disease in relatives.
  • Medical history: A history of heart failure symptoms, rhythm problems and passing out is important.
  • Physical exam: Special attention should be paid to the cardiac and skeletal muscle systems.
  • Cardiac testing: An echocardiogram is the most common first test used to diagnose

HCM, as the characteristic thickening of the heart walls is usually visible on the echocardiogram. To further define the muscle abnormality and to determine if there is scar in the heart a cardiac magnetic resonance imaging (MRI) may be ordered. Other tests: Blood tests, electrocardiogram (EKG), exercise stress echo test and cardiac catheterization may also be recommended.

The treatment for individuals with HCM is different for each person and is based on a number of features including the presence of outflow tract obstruction (blood isn’t able to leave the left ventricle because of the thickened muscle), the function of the heart (how well it is squeezing), the presence of any symptoms, the age and activity level of the patient, the presence of abnormal heart rhythms and the family history. Treatment is aimed at minimizing or preventing symptoms and reducing the risk of complications such as heart failure and sudden cardiac arrest.

Individuals with HCM need to be followed by a cardiologist on a regular basis. Medications are used to treat symptoms and prevent further complications. Medications such as beta-blockers and calcium channel blockers relax the heart muscle, allowing it to function more efficiently. Other medications may be prescribed as needed to control heart rate or decrease the occurrence of arrhythmias.

Lifestyle changes are recommended for some individuals. Specifically, participating in competitive or endurance sports places individuals at higher risk for heart rhythm problems and are not recommended for individuals with HCM. A medical procedure may be needed if the heart muscle becomes too thick or if a rhythm problem is detected.

Most people with HCM have a low risk for sudden cardiac death. However, it is important to identify the small number of patients with HCM who do have a higher risk for sudden cardiac arrest, so preventive measures can be taken. A physician can assess an individual’s risk and may prescribe preventive treatments such as antiarrhythmic medications or an implantable cardioverter defibrillator (ICD) to reduce the chance of a sudden cardiac death.

Talk to your doctor about if genetic testing and routine cardiac screening may be right for your child and your family. Learn more about Cardiomyopathy Genetic Testing and Screening for Families.

The Cardiomyopathy Association:

Children’s Cardiomyopathy Foundation:

Hypertrophic Cardiomyopathy Foundation:

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