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Thread: Hypertrophic cardiomyopathy

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    Arrow Hypertrophic cardiomyopathy

    Hypertrophic cardiomyopathy (HCM)


    Hypertrophic cardiomyopathy (HCM) is a genetic disease with an autosomal dominant pattern of inheritance. It is characterized by hypertrophy of the left ventricle (LV), with markedly variable clinical manifestations and genetic, morphologic, and hemodynamic abnormalities
    Definition
    Hypertrophic cardiomyopathy (HCM) is a disease in which the heart muscle (myocardium) becomes abnormally thick — or hypertrophied. This thickened heart muscle can make it harder for the heart to pump blood. Hypertrophic cardiomyopathy may also affect the heart's electrical system.

    In most people, hypertrophic cardiomyopathy doesn't cause severe problems and they're able to live a normal life. In a small number of people with hypertrophic cardiomyopathy, the thickened heart muscle can cause symptoms such as shortness of breath, problems in the heart's electrical system resulting in life-threatening arrhythmias and sudden cardiac death. Hypertrophic cardiomyopathy is the most common cause of heart-related sudden death in people under 30. Fortunately, death and severe complications are relatively rare and researchers are exploring new treatment and prevention options.

    Symptoms


    Possible signs and symptoms include:

    •Shortness of breath, especially during exercise or exertion
    •Chest pain, especially during exercise or exertion
    •Fainting, especially during exercise or exertion
    •Dizziness
    •Fatigue
    •Heart palpitations — the sensation of rapid, fluttering or pounding heartbeats
    Causes
    Hypertrophic cardiomyopathy is usually caused by gene mutations. It's thought these mutations cause the heart muscle to grow abnormally thick. People with hypertrophic cardiomyopathy also have an abnormal arrangement of heart muscle fibers. The heart muscle cells become jumbled, known as myofiber disarray. This disarray can contribute to an irregular heartbeat (arrhythmia) in some people.

    The severity of hypertrophic cardiomyopathy varies widely. Most people with hypertrophic cardiomyopathy have a form of the disease in which the wall (septum) between the two bottom chambers of the heart (the ventricles) becomes enlarged and obstructs blood flow. This is sometimes referred to as hypertrophic cardiomyopathy with obstruction or hypertrophic obstructive cardiomyopathy. About 70 percent of those with hypertrophic cardiomyopathy have some form of obstruction.

    Sometimes hypertrophic cardiomyopathy occurs without significant obstruction of blood flow. However, the heart's main pumping chamber (the left ventricle) may become stiff, which reduces how much blood the ventricle can hold and how much blood gets pumped out to the body with each contraction. Doctors sometimes refer to this as hypertrophic cardiomyopathy without obstruction, or nonobstructive hypertrophic cardiomyopathy.

    Pathophysiology of obstructive hypertrophic cardiomyopathy

    The consequences of HCM gene mutations appear to be directly related to the dominant negative effect exerted on sarcomere function . Hemodynamic dysfunction precedes the histopathology, implying that the hypertrophic phenotype is a compensatory response to sarcomere mutations .

    Although the relationship to the contractile gene mutations is not clear, one study reported that patients with HCM have increased levels of transforming growth factor-beta-1 and insulin-like growth factor-I which may be responsible for the abnormal hypertrophy. The mRNA and protein levels of these two factors were 2.0 and 2.9 times higher than those in the hypertrophic myocardium secondary to aortic stenosis, 2.3 and 4.7 times higher than their levels in nonhypertrophied myocardium in patients with angina and 3.0 and 5.7 times higher than those in a dilated ischemic cardiomyopathy.

    In a subset of patients, the site and extent of cardiac hypertrophy results in obstruction to left ventricular outflow . This topic will review the types and pathophysiology of the obstruction and its clinical consequences.


    TYPES OF OBSTRUCTION IN HCM

    There is significant interpatient variability in the degree of LV outflow obstruction in HCM. Significant LV outflow obstruction is present at rest in some patients with HCM each time they are seen and evaluated . In others, there is no evidence of LV outflow obstruction at rest, but significant obstruction occurs under certain conditions.

    LV outflow tract obstruction can be induced or increased by maneuvers that reduce preload (chamber size), decrease afterload, or increase left ventricular inotropy. Preload is reduced by dehydration, sudden adoption of the upright posture, the Valsalva maneuver, and amyl nitrite inhalation. Examples of increased inotropy include fever, after exercise, isoproterenol infusion, or after a premature beat which results in postextrasystolic potentiation .

    LV outflow obstruction can be reduced or eliminated by maneuvers that increase chamber size. This can be achieved by enhancing venous return and preload (eg, by squatting or leg elevation) or by raising afterload (eg, by handgrip). Drugs that reduce inotropy (eg, beta blockers and calcium channel blockers) also diminish obstruction.


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    Last edited by trimurtulu; 01-01-2009 at 09:50 AM.

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