What Is Hypertrophic Cardiomyopathy?

A Common Genetic Heart Disorder

Doctor performing heart checkup on patient

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Hypertrophic cardiomyopathy (HCM) is a relatively common genetic disorder of the heart (affecting almost one in 500 people) that can cause several problems, including heart failure and sudden death. However, the severity of HCM is quite variable from person to person, and many people with HCM can lead virtually normal lives.

Causes

HCM is caused by one or another of several genetic mutations that produce a disorder in the growth of the heart muscle fibers. HCM is passed on as an “autosomal dominant” trait, which means that if the abnormal gene is inherited from a single parent, the child will have the disease.

However, in almost half the patients with HCM, the genetic disorder is not inherited at all but occurs as a spontaneous gene mutation—in which case, the parents and siblings of the patient will not be at elevated risk for HCM. However, this “new” mutation can be passed on to the next generation. 

Cardiac Effects

In HCM, the muscular walls of the ventricles (the lower chambers of the heart) become abnormally thickened—a condition called hypertrophy. This thickening causes the heart muscle to function abnormally to some extent. If severe, the hypertrophy can lead to heart failure and cardiac arrhythmias

In addition, if it becomes extreme, the hypertrophy can cause a distortion in the ventricles, which can interfere with the function of the mitral valve and can cause an obstruction below the aortic valve, disrupting the flow of blood through the heart.

HCM can cause at least five kinds of serious cardiac problems:

Diastolic Dysfunction

Diastolic dysfunction refers to an abnormal stiffness of the ventricular muscle, which makes it more difficult for the ventricles to fill with blood in between each heartbeat. In HCM, the hypertrophy itself produces at least some diastolic dysfunction.

If severe enough, this diastolic dysfunction can lead to diastolic heart failure, and severe symptoms of dyspnea (shortness of breath) and fatigue. Even relatively mild diastolic dysfunction makes it more difficult for patients with HCM to tolerate cardiac arrhythmias, especially atrial fibrillation.

Left Ventricular Outflow Obstruction (LVOT)

In LVOT, there is a partial obstruction making it difficult for the left ventricle to eject blood with each heartbeat. This problem also occurs with aortic valve stenosis, in which the aortic valve becomes thickened and fails to open normally.

However, while aortic stenosis is caused by disease in the heart valve itself, the LVOT with HCM is caused by a thickening of the heart muscle just below the aortic valve. This condition is referred to as subvalvular stenosis. Just as with aortic stenosis, the LVOT caused by HCM can lead to heart failure.

Mitral Regurgitation

In mitral regurgitation, the mitral valve fails to close normally when the left ventricle beats, allowing blood to flow backward (“regurgitate”) into the left atrium. The mitral regurgitation seen with HCM is not caused by an intrinsic heart valve problem, but rather, is produced by a distortion in the way the ventricle contracts, caused by the thickening of the ventricular muscle. Mitral regurgitation is yet another mechanism by which people with HCM can develop heart failure.

Ischemia of the Heart Muscle

Ischemia, or oxygen deprivation, is most typically seen in patients with coronary artery disease (CAD), in which a blockage in a coronary artery limits blood flow to a portion of heart muscle. With HCM, the heart muscle can become so thickened that some portions of the muscle simply do not receive enough blood flow, even when the coronary arteries themselves are completely normal. When this happens, angina can occur (especially with exertion), and a myocardial infarction (death of heart muscle) is even possible.

Sudden Death

Sudden death in HCM is usually due to ventricular tachycardia or ventricular fibrillation.

Most of the arrhythmias that lead to sudden death are not related to ischemia—they are generally related to abnormal heart muscle as a result of cellular disarray and fibrosis. Ischemia can exacerbate the situation, however.

Symptoms

The symptoms experienced by people with HCM are quite variable. It is common for patients with mild disease not to have any symptoms at all. However, if any of the heart problems just mentioned are present, at least some symptoms are likely.

The most common symptoms experienced by patients with HCM are:

Syncope in anyone with HCM, especially if it is associated with exercise, is a very serious matter, and may indicate a very high risk of sudden death. Any episode of syncope needs to be evaluated right away by a doctor.

Diagnosis

In general, a cardiac magnetic resonance imaging scan (MRI) is the best method of diagnosing HCM, however an echocardiogram is also very useful and is often one of the first tests requested due to availability and cost. Both tests can allow for an accurate measurement of the thickness of the ventricular walls and can detect LVOT and mitral regurgitation as well. 

The electrocardiogram (ECG) can reveal left ventricular hypertrophy and has been used as a screening tool to look for HCM in young athletes. 

Both an ECG and echocardiogram should be performed in close relatives of anyone diagnosed with HCM, and an echocardiogram should be performed in any person in whom the ECG or the physical examination suggests ventricular hypertrophy.

Treatment

HCM cannot be cured, but in most cases, medical management can control symptoms and improve clinical outcomes. However, the management of HCM can become quite complex, and anyone who has symptoms due to HCM should be followed by a cardiologist.

Beta blockers and calcium blockers are often used in HCM to help alleviate symptoms. Avoiding dehydration is important in patients with HCM in reducing symptoms related to LVOT. In some patients, surgery to remove portions of the thickened heart muscle is necessary to relieve LVOT.

Atrial fibrillation, if it occurs, often causes severe symptoms and needs to be managed more aggressively in patients with HCM than in the general population.

Prevention of Sudden Death

HCM was thought to be the most common cause of sudden death in young athletes; however, newer studies may suggest otherwise. Regardless, it is still a common cause. While sudden death is always a devastating problem, it is particularly so when it occurs in young people. For this reason, anyone with HCM should contact their physician prior to any extreme exertion or competitive exercise, as there is an increased risk of sudden cardiac death.

Many methods have been tried for reducing the risk of sudden death in patients with HCM – including using beta-blockers and calcium blockers, and antiarrhythmic drugs. However, these methods have not proven sufficiently effective. It now seems clear that, in patients with HCM whose risk of sudden death appears high, an implantable defibrillator should be strongly considered.

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  1. Harmon KG, et al. Incidence, cause, and comparative frequency of sudden cardiac death in National Collegiate Athletic Association athletes: a decade in review. Circulation. 2015 Jul 7;132(1):10-9. doi:10.1161/CIRCULATIONAHA.115.015431

Additional Reading
  • Gersh BJ, Maron BJ, Bonow RO, et al. 2011 ACCF/AHA guideline for the diagnosis and treatment of hypertrophic cardiomyopathy: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Circulation 2011; 124:2761.

  • Massie, BM "Heart Failure" in Goldman L and Ausiello D (Eds). Cecil Textbook of Medicine, WB Saunders, 2003.

  • Nishimura RA, Holmes DR Jr. Clinical practice. Hypertrophic obstructive cardiomyopathy. N Engl J Med 2004; 350:1320.