Cardiomyopathies are diseases affecting heart muscle. In hypertrophic cardiomyopathy (HCM, aka idiopathic hypertrophic subaortic stenosis, asymmetric septal hypertrophy, hypertrophic obstructive cardiomyopathy) sarcomeres (units of heart muscle) enlarge, causing heart muscle cells to hypertrophy (increase in size). This causes the heart muscle to thicken unevenly and changes the way different parts of the heart move, which then requires it to work harder to pump blood. In HCM, hypertrophy usually involves the septum (wall) between the ventricles (lower heart chambers), which differs from other types of cardiomyopathy. As part of the hypertrophy process, the normal pattern of muscle cells is upset and can lead to problems with electrical function of the heart, resulting in arrhythmias (abnormal heartbeat). The first case of HCM was diagnosed 50 years ago. It has since been found to affect 0.2% to 0.5% of the general population and appears in all racial groups. It is the most common cause of sudden death in young people, including trained athletes, and causes heart failure disability at any age. This disorder is different from left ventricular hypertrophy, which is usually caused by undertreated hypertension. The October 21, 2009, issue of JAMA includes an article about HCM transmitted by sperm donation.
Transmisison of HCM is genetic (inherited). HCM is transmitted to 50% of individuals in each subsequent generation. It is due to a mutation in at least 1 of 11 genes coding for sarcomere protein. In persons without a family history of HCM, the most common cause is a new mutation.
Symptoms are shortness of breath, chest pain, dizziness, faintness, and palpitations. In children, the first sign of HCM is often sudden cardiac arrest (collapse and possible death) due to arrhythmias. Although it is possible to diagnose HCM through physical examination, most physicians confirm it through additional testing. The most common test is 2-dimensional echocardiography (ultrasonic waves directed at tissues), although magnetic resonance imaging (MRI) is becoming more widely used. Genetic testing using a blood test is the most sensitive diagnostic test. Other tests used in evaluating HCM include electrocardiogram (graphic tracing of electric potential caused by excitation of heart muscle) and 24-hour Holter monitor (monitor for heart rhythm).
Once HCM is identified in a person, all immediate family members should be tested as soon as possible. Medications such as beta-blockers or calcium channel blockers are the primary way to control symptoms. Other possible treatments include septal myectomy (removing a portion of the wall between the ventricles), alcohol septal ablation (destroying a portion of the wall), pacemakers, implantable defibrillators, and heart transplantation. Diuretics (water pills) should be avoided.
HCM can cause sudden death even in children and young adults, often during or just after vigorous exertion. However, others with HCM have no symptoms and live a normal lifespan. Remarkably, the first patient identified with HCM is still alive. He received a heart transplant in 1989.
National Institutes of Healthhttp://www.nhlbi.nih.gov/health/dci/Diseases/cm/cm_what.html
American Heart Associationhttp://www.americanheart.org
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Sources: National Institutes of Health, American Heart Association
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TOPIC: HEART DISEASE
Chang HJ, Lynm C, Glass RM. Hypertrophic Cardiomyopathy. JAMA. 2009;302(15):1720. doi:10.1001/jama.302.15.1720