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Hypertrophic Cardiomyopathy

by J. Malcolm O. Arnold, MD

Hypertrophic cardiomyopathy includes a group of heart disorders in which the walls of the ventricles thicken (hypertrophy) and become stiff.

  • Most cases of hypertrophic cardiomyopathy are caused by an inherited genetic defect.

  • People experience fainting, chest pain, shortness of breath, and awareness of irregular heartbeats.

  • Doctors suspect the diagnosis based on physical examination findings, but they use echocardiography or magnetic resonance imaging to confirm the diagnosis.

  • Drugs that reduce the force of the heart’s contractions are given.

Hypertrophic cardiomyopathy is a common cause of sudden death in young athletes (see Sudden Cardiac Death in Athletes). Perhaps 1 in 500 people is affected.

Causes

Hypertrophic cardiomyopathy is nearly always caused by an inherited genetic defect. Very rarely, people acquire hypertrophic cardiomyopathy when they have disorders such as acromegaly (excessive growth due to overproduction of growth hormone, usually by a benign pituitary tumor), a pheochromocytoma (a tumor that overproduces the hormone epinephrine ), or neurofibromatosis (a genetic disorder in which many soft, fleshy growths of nerve tissue grow under the skin and in other parts of the body).

The thick, stiff walls of the ventricles do not relax appropriately to allow the heart chambers to fill with blood. This difficulty becomes more severe when the heart beats quickly (as during exercise) because there is then even less time for the heart to fill. Because the heart does not fill properly, it pumps less blood with each beat. Sometimes the thickened heart walls also interfere with blood flow out of the heart. This variation is called hypertrophic obstructive cardiomyopathy.

Because the ventricle walls thicken, the mitral valve (the valve that opens between the left atrium and the left ventricle) may be unable to close normally, resulting in leakage of a small amount of blood back into the left atrium. This valve leakage and the enlarged ventricular walls typically cause abnormal heart sounds (heart murmurs).

Symptoms

Symptoms are highly variable, but when they occur, they usually develop when people are between ages 20 and 40. Symptoms first occur during exertion and include fainting (syncope), chest pain, shortness of breath, and sensation of irregular heartbeats (palpitations). Fainting usually occurs suddenly without any warning symptoms. Fainting or even sudden death may be the first sign that a person has this condition.

Diagnosis

Doctors usually suspect the diagnosis of hypertrophic cardiomyopathy based on the person's symptoms, the results of a physical examination, electrocardiography (ECG), and a chest x-ray. The heart sounds and any murmurs heard through a stethoscope may be helpful. Echocardiography is the best way to confirm the diagnosis, but magnetic resonance imaging (MRI) may also be used as it may provide more detailed information. Cardiac catheterization, an invasive procedure, is done to measure pressures in the heart chambers only if surgery is being considered.

Because hypertrophic cardiomyopathy is usually caused by a gene mutation, genetic testing may also be done.

Prognosis

About 1 to 3% of adults with hypertrophic cardiomyopathy die each year. Children with hypertrophic cardiomyopathy are more likely to die. Other high-risk factors include the severity of thickening in the heart muscle, the occurrence of rapid ventricular rhythms, sudden excessive exertion, and not following medical advice. 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 because they have a 50% chance of passing this disorder on to their offspring. Family members of people who have this inherited disorder may wish to consider genetic testing.

Treatment

If possible, doctors treat the underlying cause.

Treatment of hypertrophic cardiomyopathy is aimed primarily at reducing the heart’s resistance to filling with blood between heartbeats. Beta-blockers and the calcium channel blocker verapamil—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 verapamil 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 surgery is done only when symptoms are incapacitating despite drug therapy. Myectomy can relieve symptoms, but it does not reduce the risk of death. Alcohol ablation (controlled destruction of a small area of heart muscle) is increasingly being used in certain people to improve blood flow from the heart because it can be done by using cardiac catheterization. Although cardiac catheterization is an invasive procedure in which a catheter is threaded into the heart, it has fewer risks than surgery. However, when myectomy is done in hospitals that have extensive experience doing the procedure, long-term results are excellent.

In a subgroup of people with hypertrophic cardiomyopathy, a high risk of sudden death is present in those with more severe muscle thickening, especially in the wall that separates the heart chambers from each other (cardiac septum). Doctors may recommend an implantable cardioverter-defibrillator for these people.

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  • ADRENALIN
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