Hypertrophic cardiomyopathy (HCM) is a disease in which the heart muscle (myocardium) becomes abnormally thick (hypertrophied). The thickened heart muscle can make it harder for the heart to pump blood.
Hypertrophic cardiomyopathy often goes undiagnosed because many people with the disease have few, if any, symptoms and can lead normal lives with no significant problems. However, in a small number of people with HCM, the thickened heart muscle can cause shortness of breath, chest pain or problems in the heart's electrical system, resulting in life-threatening abnormal heart rhythms (arrhythmias).
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Signs and symptoms of hypertrophic cardiomyopathy may include one or more of the following:
- Shortness of breath, especially during exercise
- Chest pain, especially during exercise
- Fainting, especially during or just after exercise or exertion
- Sensation of rapid, fluttering or pounding heartbeats (palpitations)
- Heart murmur, which a doctor might detect while listening to your heart
When to see a doctor
A number of conditions can cause shortness of breath and heart palpitations. It's important to get a prompt, accurate diagnosis and appropriate care. See your doctor if you experience any symptoms associated with hypertrophic cardiomyopathy.
Call 911 or your local emergency number if you experience any of the following symptoms for more than a few minutes:
- Rapid or irregular heartbeat
- Difficulty breathing
- Chest pain
Hypertrophic cardiomyopathy is usually caused by abnormal genes (gene mutations) that cause the heart muscle to grow abnormally thick. People with hypertrophic cardiomyopathy also have an abnormal arrangement of heart muscle cells, a condition known as myofiber disarray. This disarray can contribute to arrhythmia in some people.
The severity of hypertrophic cardiomyopathy varies widely. Most people with hypertrophic cardiomyopathy have a form of the disease in which the wall (septum) between the two bottom chambers of the heart (ventricles) becomes enlarged and impedes blood flow out of the heart. This condition is sometimes called obstructive hypertrophic cardiomyopathy.
Sometimes hypertrophic cardiomyopathy occurs without significant blocking of blood flow. However, the heart's main pumping chamber (left ventricle) may become stiff, reducing the amount of blood the ventricle can hold and the amount pumped out to the body with each heartbeat. This condition is sometimes called nonobstructive hypertrophic cardiomyopathy.
Hypertrophic cardiomyopathy is usually inherited. There's a 50 percent chance that the children of a parent with hypertrophic cardiomyopathy will inherit the genetic mutation for the disease. Close relatives — parents, children or siblings — of a person with hypertrophic cardiomyopathy should ask their doctors about screening for the disease.
Many people with hypertrophic cardiomyopathy (HCM) don't experience significant health problems. But some people experience complications, including:
- Arrhythmias. Thickened heart muscle, as well as the abnormal structure of heart cells, can disrupt the normal functioning of the heart's electrical system, resulting in fast or irregular heartbeats. Atrial fibrillation, ventricular tachycardia and ventricular fibrillation are among the arrhythmias that may be caused by hypertrophic cardiomyopathy. Atrial fibrillation can also increase your risk of developing blood clots, which can travel to your brain and cause a stroke.
- Obstructed blood flow. In many people, the thickened heart muscle obstructs the blood flow leaving the heart. Obstructed blood flow can cause shortness of breath with exertion, chest pain, dizziness and fainting spells.
- Dilated cardiomyopathy. Over time, thickened heart muscle may become weak and ineffective in a very small percentage of people with HCM. The ventricle becomes enlarged (dilated), and its pumping ability becomes less forceful.
- Mitral valve problems. The thickened heart muscle can leave a smaller space for blood to flow, causing blood to rush through your heart valves more quickly and forcefully. This increased force can prevent the valve between your heart's left atrium and left ventricle (mitral valve) from closing properly. As a result, blood can leak backward into the left atrium (mitral valve regurgitation), possibly leading to worsening symptoms.
- Heart failure. The thickened heart muscle can eventually become too stiff to effectively fill with blood. As a result, your heart can't pump enough blood to meet your body's needs.
- Sudden cardiac death. Ventricular tachycardia and ventricular fibrillation can cause sudden cardiac death. People with hypertrophic cardiomyopathy have an increased risk of sudden cardiac death, although such deaths are rare. Sudden cardiac death is estimated to occur in about 1 percent of HCM patients each year. Hypertrophic cardiomyopathy can cause heart-related sudden death in people of all ages, but the condition most often causes sudden cardiac death in people under the age of 30.
Because hypertrophic cardiomyopathy is inherited, it can't be prevented. But it's important to identify the condition as early as possible to guide treatment and prevent complications.
Preventing sudden death
Implantation of a cardioverter-defibrillator has been shown to help prevent sudden cardiac death, which occurs in about 1 percent of people with hypertrophic cardiomyopathy.
Unfortunately, because many people with hypertrophic cardiomyopathy don't realize they have it, there are instances where the first sign of a problem is sudden cardiac death. These cases can happen in seemingly healthy young people, including high school athletes and other young, active adults. News of these types of deaths generates understandable attention because they're so unexpected, but parents should be aware these deaths are quite rare.
Still, experts in heart abnormalities generally recommend that people with hypertrophic cardiomyopathy not participate in most competitive sports with the possible exception of some low intensity sports. Discuss specific recommendations with your cardiologist.