Hypertrophic cardiomyopathy

Blausen 0166 Cardiomyopathy Hypertrophic

Echocardiography of hypertrophic-obstructive cardiomyopathy in a domestic cat

Hypertrophic cardiomyopathy (HCM) is a genetic disorder of the heart muscle characterized by abnormal thickening (hypertrophy) of the myocardial tissue, particularly affecting the interventricular septum. This condition leads to alterations in cardiac function and can be associated with various clinical manifestations ranging from asymptomatic cases to severe symptoms that can result in heart failure, arrhythmias, or sudden cardiac death.

Etiology

HCM is primarily an inherited disorder caused by mutations in genes encoding for proteins in the sarcomere, the contractile unit of muscle fibers. The most commonly affected genes include those encoding for:

• Beta-myosin heavy chain (MYH7)
• Myosin-binding protein C (MYBPC3)
• Troponin T (TNNT2)
• Troponin I (TNNI3)
• Alpha-tropomyosin (TPM1)

These mutations result in structural and functional abnormalities in the sarcomere, leading to hypertrophy of the myocardial tissue. Inheritance is typically autosomal dominant, although de novo mutations have been reported.

Pathophysiology

The hallmark of HCM is the thickening of the heart muscle, particularly the interventricular septum, which can cause a variety of structural and functional impairments:

• Left ventricular outflow tract (LVOT) obstruction, caused by hypertrophy of the septum, can lead to increased pressure gradients during systole.
• Diastolic dysfunction due to impaired relaxation of the hypertrophied myocardium.
• Myocardial ischemia resulting from inadequate coronary blood flow to the hypertrophied myocardium.

In some cases, the hypertrophy can lead to a phenomenon known as "heart failure with preserved ejection fraction" (HFpEF), where the heart's pumping efficiency remains normal, but its ability to relax and fill with blood is impaired.

Clinical Features

The clinical presentation of HCM can vary widely, from asymptomatic individuals to those with severe symptoms. Common manifestations include:

• Chest pain, often due to ischemia
• Dyspnea (shortness of breath)
• Syncope (fainting), often related to arrhythmias or LVOT obstruction
• Palpitations, which may be caused by arrhythmias
• Fatigue due to decreased cardiac output
• Sudden cardiac death (SCD) in young athletes, typically due to arrhythmic events

In many cases, HCM remains asymptomatic, with patients being diagnosed incidentally during family screening or evaluation for another condition.

Diagnosis

Diagnosis is based on clinical suspicion and is confirmed through a combination of:

• Echocardiography: The gold standard imaging technique for detecting hypertrophy. Key features include asymmetric thickening of the ventricular walls, particularly the interventricular septum, and evidence of LVOT obstruction.
• Electrocardiogram (ECG): May show nonspecific abnormalities such as left ventricular hypertrophy, Q waves, and arrhythmias.
• Cardiac MRI: Used in complex cases or when echocardiography is inconclusive. It can provide detailed information on myocardial thickness and fibrosis.
• Genetic testing: Identifies mutations in genes encoding sarcomeric proteins, which can help confirm the diagnosis and identify at-risk family members.

Differential Diagnosis

The following conditions should be considered in the differential diagnosis of hypertrophic cardiomyopathy:

• Athlete's heart: Physiological left ventricular hypertrophy due to endurance training.
• Valvular aortic stenosis: Can mimic HCM due to similar symptoms and LVOT obstruction.
• Fabry disease: A lysosomal storage disorder that can present with hypertrophy of the heart muscle.
• Amyloidosis: A condition characterized by deposition of amyloid fibrils in the heart, leading to thickening of the myocardium.

Treatment

The treatment of HCM aims to alleviate symptoms, reduce the risk of complications, and improve quality of life. Management options include:

• Pharmacotherapy:
• Beta-blockers and calcium channel blockers are first-line agents to relieve symptoms, particularly for patients with LVOT obstruction or diastolic dysfunction.
• Mavacamten, a myosin inhibitor, showing promising results in clinical trials with improvements in symptoms, exercise capacity, and LVOT gradients. However, it's crucial to note that it's a relatively new drug, and long-term effects and safety are still being studied.
• Disopyramide, an antiarrhythmic agent, may be used in certain cases to reduce obstruction and improve symptoms.
• Anticoagulants may be prescribed for patients with atrial fibrillation or other thromboembolic risks.

• Surgical interventions:
• Septal myectomy: A surgical procedure that removes a portion of the hypertrophied septum to alleviate LVOT obstruction.
• Alcohol septal ablation: A minimally invasive procedure where alcohol is injected into the septal artery, causing localized myocardial infarction and subsequent thinning of the hypertrophied septum.

• Implantable devices:
• Implantable cardioverter-defibrillator (ICD) is recommended for patients at high risk of sudden cardiac death, such as those with a history of arrhythmias or family history of SCD.

• Lifestyle modifications:
• Avoiding intense physical exertion is recommended, especially for competitive athletes, as strenuous activity may trigger arrhythmic events or sudden cardiac death.
• Regular follow-up with a cardiologist to monitor for complications and assess the need for device implantation.

Prognosis

The prognosis of HCM varies depending on the severity of the disease and the presence of complications such as heart failure or arrhythmias. While many individuals with HCM lead normal lives with proper management, some may experience progressive heart failure or sudden cardiac death. The overall mortality rate for individuals with HCM is low, but the risk of sudden cardiac death is higher in younger patients, particularly athletes, or those with a family history of SCD.

Prevention

Since HCM is a genetic condition, prevention involves genetic counseling and family screening. Family members of individuals diagnosed with HCM should undergo genetic testing and clinical evaluation to identify those at risk. Early detection allows for the implementation of preventive measures, such as lifestyle modifications and the use of an ICD for high-risk patients.

See Also

• Cardiomyopathy
• Congestive heart failure
• Sudden cardiac death
• Arrhythmias
• Genetic testing

External Links

• Hypertrophic Cardiomyopathy - American Heart Association
• - National Heart, Lung, and Blood Institute

See Also

• Cardiomyopathy
• Heart failure
• Cardiac arrest

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