Hypertrophic Cardiomyopathy (HCM) is a disease that affects the heart muscle, causing the muscle to enlarge, or "hypertrophy."

At Cleveland Clinic's Miller Family Heart, Vascular & Thoracic Institute, we have a special interest in treating Hypertrophic Cardiomyopathy (HCM). Since 1978, we have treated hundreds of patients and the numbers are increasing each year.

What is hypertrophic cardiomyopathy (HCM)?

Hypertrophic cardiomyopathy (HCM) is a complex type of heart disease that affects the heart muscle. It causes thickening of the heart muscle (especially the ventricles, or lower heart chambers), left ventricular stiffness, mitral valve changes and cellular changes.

Thickening of the heart muscle (myocardium) occurs most commonly at the septum. The septum is the muscular wall that separates the left and right side of the heart. Problems occur when the septum between the heart’s lower chambers, or ventricles, is thickened. The thickened septum may cause a narrowing that can block or reduce the blood flow from the left ventricle to the aorta - a condition called “outflow tract obstruction.” The ventricles must pump harder to overcome the narrowing or blockage. This type of hypertrophic cardiomyopathy may be called hypertrophic obstructive cardiomyopathy (HOCM).

HCM also may cause thickening in other parts of the heart muscle, such as the bottom of the heart called the apex, right ventricle, or throughout the entire left ventricle.

Normal Heart

Normal Heart

Stiffness in the left ventricle occurs as a result of cellular changes that occur in the heart muscle when it thickens. The left ventricle is unable to relax normally and fill with blood. Since there is less blood at the end of filling, there is less oxygen-rich blood pumped to the organs and muscles. The stiffness in the left ventricle causes pressure to increase inside the heart and may lead to the symptoms described below.

Mitral valve changes: The narrowing of the left ventricular outflow tract disrupts the proper function of the mitral valve, resulting in outflow obstruction and increased pressure in the left ventricle.

The obstruction is the result of the mitral valve striking the septum. When this occurs, the mitral valve frequently leaks, causing the blood to go back into the left atrium.

Cellular changes, or changes in the cells of the heart muscle, occur with HCM. Through a microscope, the cells appear disorganized and irregular (called “disarray”) instead of being organized and parallel. This disarray may cause changes in the electrical signals traveling through the lower chambers of the heart and lead to ventricular arrhythmia (a type of abnormal heart rhythm).

Disorganized Pattern

Disorganized Pattern

Normal Cell Pattern

Normal Cell Pattern

Who is affected by hypertrophic cardiomyopathy (HCM)?

Hypertrophic cardiomyopathy affects an estimated 600,000 to 1.5 million Americans, or one in 500 people. It is more prevalent than multiple sclerosis, which affects one in 700 people.

What causes hypertrophic cardiomyopathy (HCM)?

  • HCM can be inherited, caused by an abnormality in a gene that codes the characteristics for the heart muscle. There are many genes that can cause HCM. When a gene defect is present, the type of HCM that develops varies greatly within the family. In addition, some people who have the HCM gene may never develop the disease.
  • Hypertrophy may be acquired as a result of high blood pressure or aging.
  • In other instances, the cause of hypertrophy and HCM is unknown.

Because the cause of HCM varies, it is frequently difficult to identify a high-risk population.

What are the conditions associated with hypertrophic cardiomyopathy (HCM)?

Many people with HCM live a normal life and do not experience health-related problems.

Other people with HCM may develop heart conditions that shorten life or decrease the person’s quality of life, including:

  • Sudden cardiac arrest and sudden cardiac death: 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 after the onset of symptoms, 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. HCM may be best known for its role in cardiac arrest and subsequent death in some young professional athletes.

  • Heart failure: A condition in which the heart’s pumping power is weaker than normal.

Associated Symptoms

Symptoms associated with the presence of ventricular tachycardia or heart failure include:

  • Chest pain or pressure that usually occurs with exercise or physical activity, but also may occur with rest or after meals.
  • Shortness of breath and fatigue, especially with exertion. These symptoms are more common in adults with hypertrophic cardiomyopathy and are most likely caused by a backup of pressure in the left atrium and lungs.
  • Syncope (fainting or passing out) may affect HCM patients. Syncope with HCM may be caused by irregular heart rhythms, abnormal responses of the blood vessels during exercise, or no cause may be found.
  • Palpitations (fluttering in the chest) due to abnormal heart rhythms (arrhythmias) such as atrial fibrillation or ventricular tachycardia. Atrial fibrillation occurs in about 25 percent of those with HCM, and increases the risk for blood clots and heart failure.

Reviewed by a Cleveland Clinic medical professional.

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