HYPERTROPHIC CARDIOMYOPATHYHYPERTROPHIC CARDIOMYOPATHY
A. DEFINITION
C. SYMPTOMS
E. TREATMENTS
A hypertrophic cardiomyopathy is characerized by left and/or right ventricular enlargement which normally involves the interventricular septum. The heart pictured on the right is from a patient with hypertrophic dilated cardiomyopathy. Notice the thickness of the left ventricular wall and the intraventricular septum(IVS). A normal heart is shown on the left for comparison.
Hypertrophic Cardiomyopathy is classified by an excessive thickening on one side of the heart muscle (myocardium). The word hypertrophy means to thicken or enlarge. Like all other muscles, the heart muscle can enlarge in normal individuals as a result of prolonged athletic training or high blood pressure. However, in Hypertrophic Cardiomyopathy (HCM) the muscle thickening occurs without an obvious cause. This thickening can be evenly distributed throughout the left ventricle, in the upper septum, or at the apex of the heart. Microscopic examinations of the heart muscle in HCM will show an abnormal alignment of the muscle cells called myocardial disarray. Normal hearts have a parallel alignment of muscle cells which contrast with the irregular, disorganized alignment of muscle cells or myocardial disarray found in some parts of the heart in HCM. HCM is rare and appears to be genetically transmitted, although the severity of the disease among family members varies. Evidence of the disease is found in about one-fourth of first degree relatives of a patient with HCM.
Hypertrophic Cardiomyopathy (HCM) was first recognized in 1958 under different names such as hypertrophic obstructive cardiomyopathy, idiopathic hypertrophic sub-aortic stenosis, and muscular sub-aortic stenosis. The general term hypertrophic cardiomyopathy is now the most widely used and accepted. HCM is a relatively uncommon heart disease and its exact frequency is unknown. A paper issued by Dr. Barry Maron of the Minneapolis Heart Institute, August 1995, estimated that 1 in 500 births could be effected by HCM.HCM is diagnosed when the septum (the section of the heart that lies between the right and left chambers) is involved in the hypertrophy. Sometimes this thickening in the septum causes obstruction to blood flow as it is ejected out of the left heart chamber. This restriction to blood flow out of the heart is significant because it makes the other walls of the heart work very hard against a pressure load. The entire heart becomes stiff and has a difficult time filling with blood. Depending on the patient, the degree of thickening can be less or more localized, and sometimes obstruction to blood flow out of the left chamber can be lacking. In these cases, symptoms are absent.
The development of myocardial ischemia (lack of sufficient blood to the heart due to an obstruction of circulation) in the coronary arteries within the wall of the heart muscle can be due to a reduction in the size of the lumen (space within the artery) and a thickening of the vessel walls.
Although heart hypertrophy may be present at birth or during childhood, it is much more common for the heart to appear normal at this time. Occasionally, HCM is the cause of a stillbirth or will develop during infancy resulting with heart failure. However, heart hypertrophy more commonly develops during growth and is usually apparent by the late teens or early twenties. Children and adolescents with the condition usually come to attention when a family screening is performed after an adult in the family is found to be affected. Approximately 50% of adults with HCM show symptoms. The remainder become diagnosed during a family screening or following the detection of a murmur or abnormality on routine electrocardiogram (ECG).
Symptoms of a HCM patient vary considerably, ranging from asymptomatic (no exhibition of symptoms) to the patient with incapacitating symptoms. Most patients are asymptomatic and are relatives of other patients with HCM. Unfortunately, the first sign of disease in asymptomatic individuals may be sudden cardiac death.There is no one particular symptom or complaint which is unique HCM. Symptoms may occur at any stage in a person's life even though the condition may have been present for some time. The reason for the onset of symptoms is often not clear.The most common symptom is shortness of breath as a consequence of high pressures inside the heart. This is due to stiffness of the muscular wall of the left ventricle of the heart. Exercise capacity may be limited by breathlessness and fatigue. Most individuals experience only mild exercise limitations, but occasionally limitation is severe and a minority may have shortness of breath at rest. Approximately 90% of patients who are symptomatic will be short of breath. Chest pain is a common symptom. It is usually brought on by exertion and relieved by rest, but pain may occur at rest or during sleep and may persist. The cause of the pain is thought to be insufficient oxygen supply to the myocardium. In HCM, the main coronary arteries are usually normal, but the greatly thickened muscle demands an increased oxygen supply, which cannot be met in some circumstances. Palpitation, an abnormal rhythm of the heart, is another symptom. People may occasionally feel an extra beat or a skipped beat. Palpitation may start suddenly, appear to be very fast and may be associated with sweating or light-headedness. People with HCM may also experience light-headedness, dizziness and blackouts. Episodes of these symptoms may occur in association with exercise, palpitations or even without any stimulation.
Listening with a stethoscope during a physical examination may reveal abnormal heart sounds. Most patients have a forceful or jerky pulse and a forceful heart beat, which can be felt on the left side of the chest. Both of these reflect the thickened heart. However the most obvious abnormality on physical examination is a heart murmur, which is present in 30 - 40% of patients. The murmur is a harsh "crescendo-decrescendo" type that is heard at the left borderof the sternum. The carotid pulse can show a bifid (double) pulse. This bifid pulse occurs as a result of no obstruction to blood flowing out from the left heart chamber in the beginning, followed by an obstruction in the middle of systole, and finally by a lessening of the obstruction at the end of systole. These physical exam findings can help differentiate someone with a severely narrowed aortic valve from someone with an obstructive hypertrophic cardiomyopathy.
The most common test for HCM is the electrocardiogram (ECG). An ECG records the electrical signals from the heart and is performed by placing electrodes on the chest, wrist and ankles. In HCM, the ECG usually shows an abnormal electrical signal due to muscle thickening and disorganization of the muscle structure. The ECG findings can show an accentuation of the voltage, evidence of heart attacks through enlarged Q waves, and ST wave changes. These ECG changes can occur even if patients have never had a heart attack. ECG abnormalities are not specific to HCM and may also be found in other heart conditions. However, in about10% of the patients, the ECG may be normal or show only minor changes.
HCM can also be detected by ultrasound scan of the heart called an echocardiogram (ECHO). An ECHO produces a picture of the heart in order to easily measure excessive thickness of the heart muscle and determine the presence of significant narrowing as blood exits from the left heart. Additional equipment called "Doppler" ultrasound can produce a color image of blood flow within the heart and measure the heart's contraction and filling. Through the Doppler ultrasound, turbulent flow can be detected. Therefore, ECHO provides a very thorough assessment of HCM.
Other tests for detection that aren't used as readily include: cardiac catheterization (x-rays of the heart by using a fine tube passed from a blood vessel to the heart to see the pressures inside the heart), coronary angiography (an x-ray of the coronary arteries to determine if they are diseased), electrophysiological studies (passage of fine wires from the veins in the groin, arm or shoulder to the heart to define the risk of electrical instability by recording the response of the electrical system of the heart), exercise testing on a treadmill or bicycle (provides an objective measurement of improvement, stability or deterioration over time), a Holter monitor (for a continuous recording of the heart beat over 24 to 48 hours to detect irregularities of the heart beat), and radionuclide studies (radioactivity given by injection in order to assess the contraction and filling of the heart and estimate its blood supply at rest and exercise).
There are many treatment options available for HCM. Since there is no cure for the heart condition, these treatments aim to improve function, prevent complications, and relieve symptoms. Many individuals who have few or no symptoms do not require treatment. For those who do, the treatments available include drug treatment and surgery.
Medications are primarily given to a person who has some or all of the symptoms described earlier. The choice of treatment will vary from individual to individual but the common group of drugs used are beta-blockers. These slow the heart beat and reduce its force of contraction to relieve chest pain, breathlessness and palpitation. Beta-blockers are widely used in medical practice for HCM, other types of heart disease, and for high blood pressure. The most commonly used beta-blockers are propranolol, atenolol, sotalol, and nadolol.
The second major group of drugs used are calcium antagonists or calcium channel blockers such as verapimil. These help HCM patients by improving the compliance of the left ventricle. With calcium anatagonists, the heart can fill with blood more easily and the contractility of the left ventricle will be reduced.
Anti-arrhythmic drugs such as amiodarone or disopyramide might be used in an individualized case when an arrhythmia (irregular heart rhythm) is detected. These drugs improve and lessen symptoms possibly by reducing the force of contraction of the heart. Disopyramide has been proven to improve left ventricular diastolic properties in patients with outflow obstruction with a decrease in outflow pressure gradient. Relief of these symptoms might be due in part to improvement of diastolic function. (Matsubara, et al)Other drugs such as anticoagulants (blood thinners for patients with persistent atrial fibrillation to prevent clot formation in the atria), diuretics (to increase urine flow in order to decrease water retention), and antibiotics (for people who have turbulent blood flow in the left ventricular outflow tract or across the mitral valve in any situation where there is an increased risk of bacteria entering the bloodstream) can be taken on an individualized basis.
Surgical treatment is available to remove the part of the septum that is obstructing the left ventricular outflow tract. Surgical myectomy (removal of muscle) is successful in relieving symptoms. In this operation, the surgeon removes a portion of the thickened muscle from the septum, therefore widening the outflow tract and relieving the obstruction. Sometimes, along with myectomy, the mitral valve is replaced with an artificial valve in order to decrease mitral valve regurgitation (blood leaking back through).
Arrhythmias, irregularities of the heart beat, are a common complication. Arrhthymias such as ventricular tachycardia (a rising in heart rate from the ventricles) or atrial fibrillation (asynchronous contraction of the atrial muscle fibers so that atrial pumping ceases altogther) may require prompt treatment. Endocarditis is an infection of the heart which occurs rarely in HCM patients. Bacteria in the bloodstream can stick to the inside of the heart where it has been roughened by turbulent blood flow.
The normal electrical signal of the heart that travels down to the ventricles from the sinoatrial node may be slow or be completely blocked. If this occurs, a pacemaker will be implanted.
Overall, in patients with HCM there is an increased risk of premature death, which can occur with little or no warning and can strike at any age. However, most patients remain stable and the percentage of symptomatic patients will increase with age. Progression of HCM to a dilated cardiomyopathy and congestive heart failure is an unusual but serious occurrence.
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