What is Hypertrophic Cardiomyopathy?

HCM is a genetic disease affecting the heart muscle. The most consistent feature of HCM is excessive thickening of the wall of the heart muscle (hypertrophy = heart muscle thickening; cardiomyopathy = diseased heart muscle). The consequences of HCM to patients are related, in part or solely, to the abnormally thickened heart muscle, which in turn is a consequence of the basic genetic defect. Hypertrophy may be widespread throughout the left ventricle, though not necessarily, and there is no single "typical" pattern of muscle thickening.

The heart (specifically the left ventricle) may also thicken in other individuals who do not have HCM, either as a result of high blood pressure, obstructive heart valve disease, or even prolonged and intense athletic training in certain sports. The type of hypertrophy associated with high blood pressure is often referred to as "secondary" (i.e., a secondary consequence of the increased blood pressure). In HCM, however, the muscular thickening of the heart wall is primary, i.e., due to a genetic defect and not a reaction to other factors. In addition, when the heart muscle of HCM is viewed under a light microscope, it usually shows several particular abnormalities, the most prominent of which is called myocardial cell (myocyte) disarray or disorganization, in which normal parallel alignment of heart muscle cells has been lost and many of the muscle cells are arranged in a characteristically chaotic and disorganized pattern. It is likely that this cell disarray interferes with normal electrical transmission of impulses and predisposes some patients to irregularities of heart rhythm, as well as altering the heart contraction.

The cell structure and architecture of the HCM heart. Diagrams contrast the regular and parallel alignment of muscle cells in the normal heart (top) with the irregular, disorganized alignment of cells ("myocardial disarray") found in some areas of the HCM heart (middle). Above (bottom) is a picture of an actual area of an HCM heart (from a histologic section) showing a disorganized chaotic arrangement of cardiac muscle cells (myocytes).

Adapted from Hypertrophic Cardiomyopathy: For Patients, Their Families, and Interested Physicians, by Barry J. Maron, MD, et al., Copyright 2001, with permission from Futura Media Services, Inc., Armonk, New York