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 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).

Hypertrophic  Cardiomyopathy
Normal Heart

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.

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

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.

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.