Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy includes a group of heart disorders in which the walls of the ventricles thicken (hypertrophy) and become stiff, even though the workload of the heart is not increased.

Generally, hypertrophic cardiomyopathy affects men and women equally. But among older people, it is more common among women than among men, mainly because women live longer than men. It occurs in about 4% of older people.

Hypertrophic cardiomyopathy may be present at birth (congenital) or acquired later in life. Congenital hypertrophic cardiomyopathy is caused by an inherited genetic defect. Acquired hypertrophic cardiomyopathy may be caused by such disorders as acromegaly (excessive growth due to overproduction of growth hormone, usually by a benign pituitary tumor) and a pheochromocytoma (a tumor that overproduces the hormone epinephrine). Neurofibromatosis, a hereditary disorder, may also cause hypertrophic cardiomyopathy.

Symptoms and Diagnosis

Symptoms include fainting (syncope), chest pain, shortness of breath, and awareness of irregular heartbeats (palpitations) produced by an abnormal heart rhythm (arrhythmia). Fainting, usually after exertion, occurs because the heart does not supply the brain with enough blood. The heart cannot supply enough blood, for example, because the heart rhythm is irregular or because the stiff, thickened ventricle does not fill with blood adequately and impedes blood flow from the heart. Fainting is more likely to occur after exertion because during exertion, the heart rate increases and more blood is pumped out, thus overcoming, to some extent, the impediment to blood flow. After exertion, the heart rate slows and the amount of blood pumped out is no longer enough to overcome the impediment.

Shortness of breath develops because fluid accumulates in the lungs. Fluid accumulates because the thickened, stiff heart resists filling with blood from the lungs and blood consequently pools in the lung (pulmonary) veins.

Because the ventricle walls thicken, the mitral valve (the valve that opens from the left atrium into the left ventricle) may be unable to close normally, resulting in a small amount of leakage. This abnormality increases the risk of infective endocarditis (see Section 3, Chapter 29) for people with hypertrophic cardiomyopathy. In some people, the thickened muscle blocks the flow of blood out of the heart below the aortic valve; this variation is called hypertrophic obstructive cardiomyopathy.

Doctors can usually make a preliminary diagnosis of hypertrophic cardiomyopathy based on the results of a physical examination. For example, the heart sounds heard through a stethoscope are usually characteristic. Echocardiography (see Section 3, Chapter 21) is the best way to confirm the diagnosis. Electrocardiography (ECG) (see Section 3, Chapter 21) and a chest x-ray are also helpful. Cardiac catheterization (see Section 3, Chapter 21), an invasive procedure, is performed to measure pressures in the heart chambers only if surgery is being considered.

Prognosis and Treatment

About 4% of people with hypertrophic cardiomyopathy die each year. Death is usually sudden, presumably due to an abnormal heart rhythm. Death due to chronic heart failure is less common. People who learn that they have inherited this disorder may wish to obtain genetic counseling when they plan a family.

If acromegaly is the cause, octreotide, a synthetic hormone, may be given to block the production of growth hormone. If a pheochromocytoma is the cause, an alpha- or beta-blocker (see Section 3, Chapter 21) may be given to block the effects of epinephrine. Alternatively, the tumor that is producing the hormone may be removed surgically or destroyed by radiation therapy.

Treatment of hypertrophic cardiomyopathy is aimed primarily at reducing the heart's resistance to filling with blood between heartbeats. Beta-blockers and calcium channel blockers--taken separately or together--are the main treatment. Both reduce the extent to which heart muscle contracts, so that the heart contracts less forcefully. As a result, the heart can fill better and, if the thickened muscle was blocking blood flow, blood can flow out of the heart more easily. Also, beta-blockers and some calcium channel blockers slow the heart rate, so that the heart has more time to fill. Sometimes disopyramide, a drug that decreases the strength of heart contractions, is also used.

Surgery to remove some of the thickened heart muscle (myectomy) can improve the flow of blood from the heart, but it is performed only when symptoms are incapacitating despite drug therapy. Surgery can relieve symptoms, but it does not reduce the risk of death.

Before a dental or surgical procedure (see Section 3, Chapter 29), antibiotics are usually given to reduce the risk of infective endocarditis.