What are the other Names for this Condition? (Also known as/Synonyms)

• Apical Hypertrophic Non-Obstructive Cardiomyopathy
• HNCM (Hypertrophic Non-Obstructive Cardiomyopathy)
• Yamaguchi Syndrome

What is Hypertrophic Non-Obstructive Cardiomyopathy? (Definition/Background Information)

• Hypertrophic Non-Obstructive Cardiomyopathy (HNCM) is a subtype of hypertrophic cardiomyopathy, which is a condition affecting the heart muscle
• The term “hypertrophic” means enlargement of cells, which, in this condition, leads to a thickening of the heart muscle. The thickening can occur in the ventricle walls and/or in the septum (wall that divides the chambers of heart)
• The thickening of the muscles leads to their stiffening; but, there is no obstruction to blood flow in HNCM. However, the function of the ventricle can still be compromised, and the heart’s pumping of blood affected
• Hypertrophic Non-Obstructive Cardiomyopathy can either be hereditary, or develop spontaneously. Some underlying medical conditions, such as thyroid disease, diabetes, and obesity, may contribute towards HNCM development. The onset can occur at any age, but typically, the onset of symptoms is during adulthood (in the 30s)
• Having a family history of cardiomyopathy is a definite risk factor for developing this condition. Additional risk factors may include high blood pressure, diabetes, and thyroid disease. The exact cause of the non-inherited type is not known; but, it may be associated with spontaneous mutations
• Mutations in several genes (MYH7, MYBPC3, TNNT2, and TNNI3 genes) cause the inherited form of hypertrophic cardiomyopathy. The pattern of inheritance is autosomal dominant, in which a single copy of the defective gene in each cell of an individual is sufficient to cause the condition
• The symptoms of Hypertrophic Non-Obstructive Cardiomyopathy may include episodes of shortness of breath, chest pain and fainting, typically during and after exercise. Additionally, there could be rapid heartbeats and fatigue
• The diagnosis of Hypertrophic Non-Obstructive Cardiomyopathy involves a thorough physical examination, symptom assessment, evaluation of family medical history, echocardiography (ECG), electrocardiography (EKG), stress test, imaging studies, and coronary catheterization. If required, a biopsy of the heart muscle may be ordered
• HNCM can potentially evolve into hypertrophic obstructive cardiomyopathy, leading to blood flow obstruction. Some other complications may include backflow of blood into the heart (heart valve regurgitation), aberrant heartbeats (arrhythmia), sudden cardiac arrest, and dilated cardiomyopathy
• Hypertrophic Non-Obstructive Cardiomyopathy may be treated with lifestyle changes, medications, non-surgical procedures, and surgical implants, depending on the severity of the condition. With early diagnosis and prompt treatment, the prognosis is generally good. However, in some individuals, a cardiac arrest may the first presentation, which can even be fatal
• Currently, there are no guidelines or methods available to prevent inherited forms of hypertrophic cardiomyopathy. Nevertheless, bringing about certain lifestyle changes and treating underlying medical conditions may help avoid or reduce severity of the symptoms

Who gets Hypertrophic Non-Obstructive Cardiomyopathy? (Age and Sex Distribution)

• Hypertrophic Non-Obstructive Cardiomyopathy occurs in less than 2% of the population
• HNCM onset can occur at any age, but typically, presents in adulthood (in the 30s)
• The condition can occur in both male and female genders
• There is no racial or ethnic predilection noted

What are the Risk Factors for Hypertrophic Non-Obstructive Cardiomyopathy? (Predisposing Factors)

The following are some risk factors for Hypertrophic Non-Obstructive Cardiomyopathy:

• A family history of the condition
• High blood pressure
• Thyroid disease
• Diabetes
• Alcoholism, heavy smoking
• Being overweight
• Not engaging in regular physical activity

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Hypertrophic Non-Obstructive Cardiomyopathy? (Etiology)

Hypertrophic Non-Obstructive Cardiomyopathy, in most cases, is caused by mutations in the MYH7, MYBPC3, TNNT2, TNNI3, and some other yet unidentified genes.

• Under normal circumstances, these genes code for proteins involved in the formation of muscle structures called sarcomeres, which help the heart muscles contract properly. The sarcomeres are composed of thick and thin muscle filaments, which work in unison by attaching and releasing in a rhythmic manner, allowing the muscles to contract and relax, respectively. This process is necessary for the heart to pump blood
• The following are some known gene functions:
  • MYH7: It codes for cardiac β myosin heavy chain, a crucial component of thick filament
  • MYBPC3: It codes for cardiac myosin binding protein, associates with the thick filament and provides structural integrity required for contractions
  • TNNT2: It codes for cardiac troponin T, which is 1 of the 3 proteins of the troponin complex in thin filaments, required for muscle contractions and relaxations
  • TNNI3: It codes for cardiac troponin 1, also a part of the troponin complex
• When there is a mutation in one or many genes involved in this process, it may result in altered proteins or loss of proteins in the sarcomeres, interfering with cardiac function. However, the link between compromised sarcomere function and thickening of cardiac muscles is not well understood
• The mutations are inherited in an autosomal dominant manner. In this type of inheritance, a single copy of a defective gene in every cell of the individual is sufficient to cause disease. Typically, one inherits the condition from an affected parent
• The cause of spontaneous mutations, which lead to the non-heritable type of HNCM, is not well-understood

Additionally, individuals with conditions, such as high blood pressure, uncontrolled diabetes, and thyroid disease, are also prone to developing HNCM. However, the cause of this heart condition originating from such factors is presently unknown.

What are the Signs and Symptoms of Hypertrophic Non-Obstructive Cardiomyopathy?

The signs and symptoms associated with Hypertrophic Non-Obstructive Cardiomyopathy include:

• Chest pain (during or after exercise)
• Dizziness, fainting (after exertion)
• Shortness of breath, particularly with physical exertion (exertional dyspnea)
• Fatigue
• Palpitations; a sensation of rapid fluttering or pounding heartbeat
• Heart murmurs: It is an unusual sound heard during the heartbeat. This can be an extra beat or whooshing/swishing sound, and may be faint or loud
• Swelling of ankles, legs, abdomen, or veins in the neck
• Some individuals with HNCM may be asymptomatic and present no symptoms

Notes: Individuals with non-obstructive cardiomyopathy are reported to present milder symptoms in general, when compared to those with obstructive cardiomyopathy.

How is Hypertrophic Non-Obstructive Cardiomyopathy Diagnosed?

The diagnosis of Hypertrophic Non-Obstructive Cardiomyopathy is made with information from the following tests and procedures:

• A thorough physical examination and an assessment of symptoms
• Evaluation of personal and family medical history
• Chest X-ray to check for heart size, contour, and fluid build-up in lungs
• Electrocardiogram (EKG) to check the heart’s electrical activity
• Echocardiography (ECG or echo) uses sound waves to create a moving picture of the heart. This helps to check the size, shape, and pumping function of the heart
• Stress test: This test places stress on the heart by making it work harder and beat faster to determine, if the cardiac muscles can cope with the increased workload
• Cardiac catheterization: To check for pressure and blood flow in the heart’s chambers. It is often coupled with coronary angiography, in which a harmless dye is injected into the coronary arties and with the help of an X-ray, blood flow through heart and blood vessels can be observed
• Myocardial biopsy: A piece of the heart is removed and the cells are investigated for changes that may suggest hypertrophic cardiomyopathy
• Genetic testing to seek confirmation of the diagnosis. This may be recommended for the whole family, which can help understand if the condition is inherited

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Hypertrophic Non-Obstructive Cardiomyopathy?

The following complications may arise in individuals with Hypertrophic Non-Obstructive Cardiomyopathy:

• The condition may evolve into hypertrophic obstructive cardiomyopathy, which can additionally result in obstruction of the blood flow
• Heart valve regurgitation: It causes the heart to pump ineffectively, such that blood flows back into the heart
• Arrhythmias: Abnormal heart rhythm, which can be triggered by physical exertion
• Sudden cardiac arrest (which can be unexpected)
• Embolism: Development of blood clots in the heart which may get into the bloodstream and obstruct blood supply to many important organs
• Edema: Fluid buildup in the lungs, abdomen, legs, and feet; all consequences of ineffective heart pumping
• Heart failure
• Dilated cardiomyopathy: It results from the heart muscles becoming inefficient, such that the pumping of blood is seriously compromised

Note: The risk for complications is lower in the non-obstructive form of hypertrophic cardiomyopathy, when compared to the obstructive form.

How is Hypertrophic Non-Obstructive Cardiomyopathy Treated?

Hypertrophic Non-Obstructive Cardiomyopathy may be treated in the following manner:

• Beta blockers and calcium channel blockers, generally the first choice of medicines to treat cardiomyopathies
• Other prescription medications may help in:
  • Regulating high blood pressure levels
  • Slow heart rate
  • Maintain normal heart beat rhythm
  • Balance electrolytes in the body; electrolytes are minerals that help in the proper functioning of muscles and nerve tissues
  • Removing excess fluid and sodium
  • Preventing blood clot formation (through anti-coagulants or blood thinners)
  • Reducing inflammation 
• Non-surgical procedures, such as alcohol septal ablation, in which:
  • Ethanol (a type of alcohol) is injected into a small artery
  • The alcohol kills cells in the tissue, to shrink the heart muscle to a more ‘normal’ size
  • This improves blood flow through the ventricles, which in turn improves the symptoms

Surgical procedures:

• Septal myectomy:
  • It is a type of open-heart surgery that is typically used for obstructive hypertrophic cardiomyopathy with severe symptoms
  • The procedure is usually recommended for young patients with poor response to medicines
  • It helps in improving blood pumping by removing part of the thickened heart muscle
• Surgically-implanted devices such as implantable cardioverter defibrillator (ICD):
  • It is a small device implanted in the chest or abdomen and connected to the heart via wires
  • The device helps control life-threatening arrhythmias that can lead to sudden cardiac arrest

Lifestyle changes:

• Adhering to a healthy diet that includes fresh fruits, vegetables, whole grains, fish and dairy products
• Engaging in routine physical activity
• Smoking cessation
• Losing excess weight
• Avoiding alcohol and illicit drugs
• Getting enough sleep
• Avoiding or reducing of stress
• Seeking treatment for underlying conditions (such as diabetes, high blood pressure)

How can Hypertrophic Non-Obstructive Cardiomyopathy be Prevented?

Hypertrophic Non-Obstructive Cardiomyopathy is a genetic condition in a majority of the affected individuals, and therefore, there are no guidelines or specific methods for preventing the condition from developing.

• Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
• If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
• Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders such as Hypertrophic Non-Obstructive Cardiomyopathy
• Regular medical screening at periodic intervals with tests and physical examinations are strongly recommended
• Some lifestyle changes, such as following a healthy diet, quitting cigarettes, reducing alcohol drinking, getting regular exercise and reducing stress, may help prevent the severity and complications from the condition
• In high-risk individuals, an implantable cardioverter defibrillator may help prevent sudden cardiac arrest, a potential complication of hypertrophic cardiomyopathy

What is the Prognosis of Hypertrophic Non-Obstructive Cardiomyopathy? (Outcomes/Resolutions)

• The prognosis of Hypertrophic Non-Obstructive Cardiomyopathy is improved with timely treatment. Adequate treatment can help prevent worsening of the condition, control symptoms, and reduce complications, leading to better outcomes
• Without treatment, the prognosis is typically poor, since symptoms can worsen and complications can follow 

Additional and Relevant Useful Information for Hypertrophic Non-Obstructive Cardiomyopathy:

Please visit our Heart & Vascular Health Center for more physician-approved health information:

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