Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a condition characterised by the thickening of the heart muscle without an obvious cause. This primarily affects the interventricular septum and ventricles, leading to impaired blood pumping and potential electrical conduction problems within the heart. HCM can be inherited, often displaying an autosomal dominant pattern, and may result from mutations in genes associated with heart muscle proteins. Other causes include Fabry disease, Friedreich's ataxia, and certain medications.

Signs and Symptoms

Many individuals with HCM are asymptomatic or experience mild symptoms. When symptoms do occur, they can include shortness of breath, chest pain, palpitations, lightheadedness, and fainting. These symptoms are largely due to the thickened left ventricle, which impairs ventricular filling and increases pressure in the left ventricle and atrium, leading to pulmonary congestion. Major risk factors for sudden death in HCM include a history of cardiac arrest, ventricular tachycardia, abnormal exercise blood pressure, unexplained syncope, and significant left ventricular wall thickness.

Diagnosis

Diagnosis of HCM involves using echocardiography, cardiac catheterisation, and cardiac MRI, along with ECG and genetic testing. A family history of HCM or unexplained sudden death is also very important. Cardiac MRI can show thickening of the ventricular septum and identify cardiac tissue scarring and inflammation. ECG is particularly sensitive, especially when left ventricular hypertrophy and right atrial enlargement are present.

Pathophysiology

Ventricular hypertrophy in HCM causes a dynamic pressure gradient across the left ventricular outflow tract (LVOT). The mitral valve leaflets may be pulled towards the septum, further obstructing blood flow. This obstruction can increase during systole due to the Venturi effect, where the increased blood flow velocity through the narrowed outflow tract reduces pressure, pulling the mitral valve anteriorly.

Treatment

Asymptomatic Patients

Asymptomatic individuals with HCM should avoid strenuous activities. Those with outflow obstructions should avoid dehydration and vasodilatory or diuretic medications. Septal reduction therapy is not recommended for asymptomatic patients.

Medications

Beta blockers are first-line treatments to slow heart rate and reduce ectopic beats. Calcium channel blockers like verapamil can be used if beta blockers are not tolerated, but caution is advised in patients with severe symptoms. Disopyramide may be used for additional symptom relief. Diuretics can be considered for fluid overload but should be used cautiously. Newer treatments like cardiac myosin inhibitors, such as mavacamten, have shown promise in reducing left ventricular outflow tract gradients.

Surgical Septal Myectomy

This open-heart surgery reduces left ventricular outflow tract obstruction and improves symptoms. It involves removing a portion of the interventricular septum and has a success rate of 85% with less than 1% surgical mortality in experienced centres.

Alcohol Septal Ablation

This less invasive procedure involves injecting alcohol into the septal branches of the left anterior descending artery to induce a controlled heart attack, resulting in scar tissue formation that reduces obstruction.

Implantable Devices

Pacemakers and implantable cardioverter-defibrillators (ICDs) may be used in patients at high risk for sudden cardiac death. Dual-chamber pacemakers can reduce outflow tract obstruction and improve symptoms.

Cardiac Transplantation

In cases unresponsive to other treatments, cardiac transplantation is an option, particularly for end-stage heart failure.

Screening

Screening for HCM involves echocardiography and ECG, particularly in young athletes, as HCM is a leading cause of sudden cardiac death in this group. Genetic testing may also be performed to identify at-risk family members.

Children

HCM is one of the most uncommon cardiac malformations in children, often diagnosed through assessment for murmur, heart failure, and genetic testing. Treatment aims to reduce symptoms and the risk of sudden death, often using beta blockers and calcium channel blockers.

Epidemiology

HCM affects about 0.2% of the global population, with a higher prevalence in males. It often presents in the third decade of life but can occur at any age.

Other Animals

Cats

Feline HCM is the most common heart disease in domestic cats, with similar genetic patterns to humans. It is diagnosed through echocardiography and treated with medications to manage symptoms and prevent thromboembolism.

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Self-assessment MCQs (single best answer)

Which part of the heart is primarily affected in hypertrophic cardiomyopathy (HCM)?

What genetic pattern does hypertrophic cardiomyopathy (HCM) often display?

Which of the following is NOT a common symptom of HCM?

What is the first-line medication treatment for symptomatic HCM?

Which diagnostic tool is particularly sensitive for detecting left ventricular hypertrophy and right atrial enlargement in HCM?

In which population is screening for HCM particularly recommended?

What surgical procedure is performed to reduce left ventricular outflow tract obstruction in HCM?

What is the role of implantable cardioverter-defibrillators (ICDs) in the treatment of HCM?

Which of the following is NOT a risk factor for sudden death in HCM?

Feline HCM shares similar genetic patterns to human HCM. Which diagnostic tool is used to diagnose HCM in cats?