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Caring for Patients with Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is an inherited disorder of the cardiac muscle characterized by increased heart mass and abnormal diastolic function. Prognosis varies in HCM; some patients are asymptomatic and lead a normal life, while others experience complications. HCM is the leading cause of sudden death in healthy children, young adults, and trained athletes.
HCM occurs in persons of all ages, both genders, and all races. The condition is caused by mutations in genes that encode components of the sarcomere (i.e., the basic functional unit of striated muscle); mutations in the β-myosin heavy chain (MYH7) and myosin binding protein C (MYBPC3) genes account for 80-85% of cases. In HCM, the typical pattern of heart muscle cells along the septum and ventricles is disorganized (i.e., perpendicular or oblique versus parallel and in an end-to-end pattern), leading to asymmetrical heart muscle hypertrophy (i.e., thickening of the septum and the left ventricle), making the heart stiff, reducing the size of the ventricular cavities, impairing blood flow, altering mitral valve function, and increasing the amount of time required for the ventricles to relax following systole. In HCM, the heart must increase the forcefulness of contractions to ensure proper ventricular filling and systolic squeeze. The disorganized pattern of heart muscle cells characteristic of HCM can interrupt typical conduction patterns, leading to cardiac arrhythmias (e.g., ventricular fibrillation, atrial fibrillation). Coronary artery walls may also be hypertrophied, decreasing their diameter and limiting blood flow to the heart muscle, resulting in areas of cardiac muscle ischemia, necrosis, and scarring, further restricting the heart's ability to contract. In approximately 25% of HCM cases, hypertrophy of the septum results in contact with mitral valve leaflets during systole, which obstructs the outflow of blood and leads to left ventricular outflow tract obstruction (LVOTO). Additional complications of HCM include mitral regurgitation, infective mitral endocarditis, heart failure (HF), and sudden death due to cardiac arrhythmias.
Patients may have a normal physical exam or present with symptoms of HF. Signs and symptoms of HCM often present before age 20 years and may include dyspnea, angina, heart palpitations, and syncope. Diagnosis is confirmed by cardiac testing, including EKG and echocardiography showing increased wall thickness of ≥1.5 cm in adults, or more than 3 standard deviations from predicted.There is no cure for HCM. Lifestyle modifications (e.g., diet modifications, avoiding strenuous exercise, preventing dehydration) can improve symptoms and prevent complications. Treatment may include symptom management with medications, such as calcium channel blockers or beta blockers. In the presence of HF, pharmacologic management varies based on the extent of diastolic and systolic dysfunction, but may include angiotensin-converting enzyme (ACE) inhibitors, beta blockers, diuretics, digoxin, or calcium channel blockers. Invasive treatments to decrease obstruction may include removing (e.g., with septalmyectomy) or damaging (e.g., alcohol septal ablation) a portion of the septum wall or replacing the mitral valve with a smaller valve (either mechanical or biologic). A defibrillator or pacemaker may be implanted to resolve arrhythmias, and alter electrical conduction. Heart transplantation is reserved for end-stage disease, and patients with signs and symptoms of HF that do not respond to pharmacologic treatment.
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