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Hypertrophic cardiomyopathy

Overview

Hypertrophic cardiomyopathy (HCM) is a disease in which the heart muscle becomes thickened (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. However, in a small number of people with HCM, the thickened heart muscle can cause shortness of breath, chest pain or changes in the heart's electrical system, resulting in life-threatening irregular heart rhythms (arrhythmias) or sudden death.

Signs, Symptoms and Risks

Some people with hypertrophic cardiomyopathy don’t have symptoms while others may only feel symptoms with exercise or exertion. Some people may not have signs or symptoms in the early stages of the disease but may develop them over time. 

Knowing the signs and symptoms of HCM is important. It can help with getting an early diagnosis when treatment may be most effective.

Signs and symptoms of HCM include:

  • Chest pain, especially with physical exertion
  • Shortness of breath, especially with physical exertion
  • Fatigue
  • Arrhythmias (abnormal heart rhythms)
  • Dizziness
  • Lightheadedness
  • Fainting (syncope)
  • Swelling in the ankles, feet, legs, abdomen

HCM is a chronic disease that can get worse over time. This can lead to poorer function and quality of life, long-term complications and more financial and social burden. 

People with HCM may need to make lifestyle changes, such as limiting their activity, to adjust for their disease.  

As HCM progresses, it can cause other health problems. People with HCM are at higher risk for developing atrial fibrillation, which can lead to blood clots, stroke and other heart-related complications. HCM may also lead to heart failure. It can also lead to sudden cardiac arrest, but this is rare. 

HCM has been regarded as the most common cause of sudden cardiac death in young people and competitive athletes in North America, although it is rare.

Causes

There are several potential causes of hypertrophic cardiomyopathy, including:

Genetics. You can inherit hypertrophic cardiomyopathy from your parents and pass it on to your children. This means something is wrong with a gene that codes the characteristics of the heart muscle. There are many genes that can cause hypertrophic cardiomyopathy. When a gene defect is present, the type of hypertrophic cardiomyopathy that develops varies greatly within the family. Some people who have the hypertrophic cardiomyopathy gene may never develop the disease.

  • High blood pressure.
  • Aging.
  • Sometimes the cause of hypertrophic cardiomyopathy is unknown.

Risk factors

Hypertrophic cardiomyopathy is usually passed down through families (inherited). People with one parent with hypertrophic cardiomyopathy have a 50% chance of having the genetic mutation for the disease.

Parents, children or siblings of a person with hypertrophic cardiomyopathy should ask their health care providers about screening for the disease.

Complications

Complications of hypertrophic cardiomyopathy can include:

Atrial fibrillation. A thickened heart muscle and changes in the structure of heart cells can cause changes in the heart's electrical system, resulting in fast or irregular heartbeats. Atrial fibrillation can also increase the risk of developing blood clots, which can travel to the brain and cause a stroke.

Blocked blood flow. In many people, the thickened heart muscle blocks the blood flow leaving the heart, causing shortness of breath with exertion, chest pain, dizziness and fainting spells.

Mitral valve disease. If the thickened heart muscle blocks the blood flow leaving the heart, the valve between the left atrium and left ventricle (mitral valve) might not close properly. As a result, blood can leak backward into the left atrium (mitral valve regurgitation), possibly making symptoms worse.

Dilated cardiomyopathy. In a small number of people with HCM, the thickened heart muscle becomes weak and ineffective. The ventricle becomes enlarged (dilated), and it pumps less forcefully.

Heart failure. The thickened heart muscle can eventually become too stiff to fill the heart with blood. As a result, the heart can't pump enough blood to meet the body's needs.

Fainting (syncope). An irregular heartbeat or blockage of blood flow can sometimes cause fainting. Unexplained fainting can be related to sudden cardiac death, especially if it's happened recently and in a young person.

Sudden cardiac death. Rarely, hypertrophic cardiomyopathy can cause heart-related sudden death in people of all ages. Because many people with hypertrophic cardiomyopathy don't realize they have it, sudden cardiac death might be the first sign of the condition. It can happen in seemingly healthy young people, including high school athletes and other young, active adults.

Prevention

There is no known prevention for hypertrophic cardiomyopathy. It's important to identify the condition as early as possible to guide treatment and prevent complications.

If you have a first-degree relative — a parent, sibling or child — with hypertrophic cardiomyopathy, you might be referred for genetic testing to screen for the condition. However, not everyone with HCM has a currently detectable mutation. Also, some insurance companies don't cover genetic testing.

If genetic testing isn't done, or if the results aren't helpful, then a health care provider might recommend repeated echocardiograms if you have a family member with hypertrophic cardiomyopathy. Adolescents and competitive athletes should be screened once a year. Adults who don't compete in athletics should be screened every five years.

Getting a Diagnosis 

Hypertrophic cardiomyopathy is most often inherited and is the most common form of genetic heart disease. It can happen at any age, but most receive a diagnosis in middle age. 

It’s estimated that 1 in every 500 people have HCM, but a large percentage of patients are undiagnosed. Of those diagnosed, two-thirds have obstructive HCM and one-third have non-obstructive HCM.

A cardiologist or pediatric cardiologist often diagnoses and treats HCM. You may also be referred to a cardiomyopathy center where the health care team has specialized training.

HCM is diagnosed based on your medical history, family history, a physical exam and diagnostic test results.  

Medical and Family Histories

Knowing your medical history and any signs and symptoms you may have is an important first step. Because HCM can be passed from parents to children, your physician will also want to know if anyone in your family has been diagnosed with HCM, heart failure or cardiac arrest. If someone has been diagnosed with HCM, first degree relatives which include siblings and parents, should also be checked.

Physical Exam

Your doctor will listen to your heart and lungs with a stethoscope. If they hear a swishing or whooshing sound called a murmur, that could mean there is problem with blood flow through the heart which may suggest HCM.  

Diagnostic Tests

Diagnosis is typically done by echocardiogram. It checks the thickness of the heart muscle and blood flow through the heart. In some cases, another type of echocardiogram, transesophageal echo (or TEE), may be performed. A TEE is done using a probe inserted in the throat while the patient is under sedation.

Other diagnostic tests may include:

  • Electrocardiogram (ECG)
  • Cardiac magnetic resonance imaging (MRI)
  • Stress tests
  • Holter and event monitors to detect abnormal heart rhythms (arrhythmias)
  • Genetic testing
  • Diagnostic Procedures

Confirming diagnosis or preparing for surgery may also involve one or more medical procedures during cardiac catheterization.

Treatment and Management of HCM

There is currently only one disease-specific medication to treat hypertrophic cardiomyopathy. Mavacamten, a medication that was approved by the FDA in April 2022, is used to treat the obstructive form of HCM in people who have symptoms.

For people with HCM who don’t have symptoms, a heart healthy lifestyle which includes staying active, eating a healthy diet, maintaining a normal weight, getting good quality sleep and not smoking  is recommended. If you have other medical conditions like high blood pressure or diabetes, it’s important that these are managed to avoid heart complications which can develop if left unchecked. 

For those with symptoms, the focus is on symptom management using medications and procedures.

Medications

Medications called beta-blockers, calcium channel blockers, antiarrhythmics and diuretics offer limited and varying relief of symptoms. They may help with function but can have side effects. 

Procedures

A range of surgical and nonsurgical procedures can be used to treat HCM:

Septal myectomy – Septal myectomy, also called septal reduction therapy, is open-heart surgery. It’s considered for people with obstructive HCM who, despite taking HCM medications, continue to have severe symptoms. A surgeon removes part of the thickened septum that’s bulging into the left ventricle. This eliminates the obstruction and restores blood flow within the heart and out to the body.

Alcohol septal ablation (nonsurgical procedure) – Also called nonsurgical septal reduction therapy, alcohol septal ablation is a procedure where ethanol (a type of alcohol) is injected through a tube into the small artery that supplies blood to the area of heart muscle thickened by HCM. The alcohol causes these cells to die. The thickened tissue shrinks to a more normal size. The risks and complications of heart surgery increase with age. For this reason, ablation may be preferred to septal myectomy in older patients with other medical conditions.

Cardiac implantable electronic devices (CIEDs) – Several types of devices can be implanted in the body to help the heart work better, including:

Implantable cardioverter defibrillator (ICD) – An ICD helps maintain a normal heartbeat by sending an electric shock to the heart if an irregular heartbeat is detected. This reduces the risk of sudden cardiac death.

Pacemaker – This small device uses electrical pulses to prompt the heart to beat at a normal rate. This is used for people with a heart rate that is too slow.

Cardiac resynchronization therapy (CRT) device – This device coordinates contractions between the heart’s left and right ventricles.

Heart transplant – In HCM patients with advanced, end-stage disease, a heart transplant may be considered. In this procedure, a person’s diseased heart is replaced with a healthy donor heart.

Prognosis

The long-term outcome for people with HCM is very good and most patients with HCM have normal life expectancy without significant limitations or complications.

A small number of people with HCM, however, are at risk for complications including heart failure and sudden death. The risk of heart complications can vary between families and among different members of the same family, so it’s important that your health care team identifies people who are most at risk for these complications so preventative treatment can be provided.

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