Cardiomyopathies are diseases that occur in the heart muscle. One of the most common types of cardiomyopathy is hypertrophic cardiomyopathy (HCM). It is a genetic disease that causes the heart muscle to thicken and harden, which makes it harder for the heart to pump blood.

What Is Hypertrophic Cardiomyopathy?

HCM causes hypertrophy, a condition in which the walls of the heart’s left ventricle (one of the four chambers of the heart) grow thicker and become stiff, making it more difficult for the heart to pump blood.

When the walls of the heart grow thick, they can become less flexible and make the inside of the left ventricle smaller and stiffer. This prevents the left ventricle from properly filling with blood and efficiently pumping oxygen-rich blood to the body. Thickening of the left ventricle can interfere with heart valve function and may obstruct blood flow from the heart to the body.

HCM can progress and lead to complications, including:

• Arrhythmia (irregular heartbeat or abnormal heart rhythms)
• Heart failure (when the heart doesn't pump enough blood and oxygen to meet the body’s needs)
• Stroke (when blood flow to part of the brain is blocked or a blood vessel bursts)
• Cardiac arrest (when the heart suddenly stops beating)

HCM can begin during childhood or young adulthood, but it may not cause problems until much later in life.

Detecting HCM early in the disease’s progression can be difficult. It can also be hard to diagnose in people who are athletic. Exercise can strengthen the heart and make the left ventricle grow thicker, which may mask the early stages of HCM.

HCM affects approximately 1 in 500 people in the United States. It sometimes runs in families and is one of the most common inherited heart conditions.

What Are the Symptoms of Hypertrophic Cardiomyopathy?

Many people with HCM don’t have any symptoms at all. When people do have symptoms, they may only occur during or after exercise or vigorous activity. If symptoms occur at rest, it may indicate more advanced disease.

Many people with hypertrophic cardiomyopathy do not have any symptoms at all. When people do have symptoms, they may only occur during or after exercise or vigorous activity.

Symptoms of HCM can include:

• Chest pain
• Shortness of breath
• Fatigue (extreme tiredness that doesn’t improve with rest)
• Dizziness or lightheadedness
• Syncope (fainting)
• Heart palpitations, faster heart rate, or a fluttering sensation in the chest
• Irregular heartbeat
• Swollen legs or feet

People with HCM may have one or more of these symptoms or none at all. None of the symptoms of HCM are unique, and they can all occur alongside many other health conditions.

HCM is a chronic, progressive disease that gets worse over time. If undiagnosed and untreated, it can lead to more troublesome symptoms, a lower quality of life, and possible complications. If you have problems with breathing or heart symptoms, take them seriously and discuss them with your healthcare provider.

What Causes Hypertrophic Cardiomyopathy?

The cause of hypertrophic cardiomyopathy isn’t fully understood. In some cases, the cause appears to be genetic, while others don’t seem to have a known cause.

Familial HCM

Researchers have found that around 60 percent of cases are caused by gene mutations (changes in genes). Cases related to these gene changes are passed down within families and called familial HCM.

Several genes have been identified that have mutations associated with familial HCM, including:

• MYH7
• MYBPC3
• TNNT2
• TNNI3

Each of these genes has a different function, but they are all involved in creating the proteins that make up the heart muscle.

Scientists believe that gene mutations associated with familial HCM cause abnormalities in the structure and function of heart tissue. Normally, heart muscle tissue grows in an orderly way, but in people with HCM, heart muscle fibers grow in a disorganized pattern. Ultimately, this leads to the heart muscle growing thicker and stiffer, preventing the heart from relaxing and filling with blood as it should.

Along with left ventricular abnormalities, HCM can also affect the septum (wall) between the left and right ventricles. A thickened septum can obstruct blood flow into the aorta, the large artery that carries blood from the heart to the rest of the body. This is called obstructive hypertrophic cardiomyopathy. If the thickening in your heart muscle occurs elsewhere and doesn’t block blood flow out of your heart, it’s called nonobstructive hypertrophic cardiomyopathy.

Nonfamilial HCM

About 40 percent of HCM diagnoses have no known cause and are not associated with an inherited genetic mutation. One study found that people with nonfamilial HCM tend to be diagnosed at a later age and have a less serious disease course.

Researchers are studying the potential causes of nonfamilial HCM and suspect it may be due to a combination of genetic and environmental factors. While people with nonfamilial HCM don’t have a family history of the condition or family members with the disease, some still express genetic changes related to the disease. Research has also linked hypertension, or high blood pressure, with nonfamilial HCM.

Could You Have Hypertrophic Cardiomyopathy?

Familial HCM is inherited in an autosomal dominant pattern. This means that you only need to inherit one copy of a mutated gene from one parent in order to develop the disease. A person with familial HCM has a 50 percent chance of passing this gene on to their child.

If you have a close family member with HCM, such as a parent, grandparent, or sibling, then you are at greater risk of having HCM. However, HCM may go undiagnosed in many people with a higher risk who do not have obvious symptoms of the condition. Also, some people who inherit the genetic mutation for familial HCM never develop symptoms, making it harder to trace genetically.

If you have a close family member with HCM, such as a parent, grandparent, or sibling, then you are at greater risk of having HCM.

Even for someone who does have symptoms, diagnosing HCM can be difficult because symptoms of the condition are also seen in other medical conditions. HCM is usually diagnosed by a cardiologist, with a thorough medical history and physical exam followed by imaging and laboratory tests such as echocardiogram, cardiac MRI, and genetic testing. A careful and accurate diagnosis of HCM is extremely important for determining the appropriate HCM treatment.

If you’re diagnosed with HCM, your healthcare provider will recommend that all of your first-degree relatives — including parents, children, and siblings — be screened for HCM as soon as possible.

Sudden Cardiac Death

Some people with HCM may have a higher risk of sudden cardiac death (SCD), though this is rare. Sudden cardiac death can also occur in people with undiagnosed HCM who have never had any symptoms.

If you know you’re at higher risk of having HCM or if you have a family history of SCD, talk to your doctor before participating in vigorous physical activity, such as football, basketball, soccer, or running. SCD tends to affect older people as well as young athletes. In fact, HCM is often considered the most common cause of sudden cardiac death among young athletes. Sometimes, implantable cardioverter defibrillators (ICDs) are recommended to protect you from SCD if you’ve been diagnosed with HCM.

Knowing the symptoms of HCM — and, more importantly, understanding your risk of developing the condition — can help you avoid serious complications of HCM. If you think you may be at risk of HCM, be sure to get medical advice before serious complications arise.

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