Cardiomyopathy is a chronic and sometimes progressive disease in which the heart muscle (myocardium), is abnormally enlarged, thickened and/or stiffened. The condition typically begins in the walls of the heart's lower chambers (ventricles), and in more severe cases also affects the walls of the upper chambers (atria). The actual muscle cells as well as the surrounding tissues of the heart become damaged. Eventually, the weakened heart loses the ability to pump blood effectively and heart failure or irregular heartbeats (arrhythmias or dysrhythmia) may occur.
Cardiomyopathy is classified as either "ischemic" or "nonischemic". All cases related to children and teenagers are considered "nonischemic" cardiomyopathy. Non-ischemic cardiomyopathy predominately involves the heart's abnormal structure and function. It does not involve the hardening of arteries on the heart surface typically associated with ischemic cardiomyopathy. Nonischemic cardiomyopathy can then be broken down into: 1) "primary cardiomyopathy" where the heart is predominately affected and the cause may be due to infectious agents or genetic disorders and 2) "secondary cardiomyopathy" where the heart is affected due to complications from another disease affecting the body (i.e. HIV, cancer, muscular dystrophy or cystic fibrosis).
Cardiomyopathy is nondiscriminatory in that it can affect any adult or child at any stage of their life. It is not gender, geographic, race or age specific. It is a particularly rare disease when diagnosed in infants and young children. Cardiomyopathy continues to be the leading reason for heart transplants in children. Currently there are no published reports specifying the total number of children affected but it is roughly estimated to be in the hundreds of thousands when all forms of cardiomyopathy are taken into account. According to the national pediatric cardiomyopathy registry, 1 in every 100,000 children in the U.S. under the age of 18 is diagnosed with primary cardiomyopathy. This annual incidence rate, however, is extremely conservative. This number excludes the increasing number of children with secondary cardiomyopathy and the large pool of undiagnosed, asymptomatic cases.
There are numerous causes for a complex disease such as cardiomyopathy. For the majority of diagnosed children, the exact cause remains unknown (termed "idiopathic"). In some cases, it may be related to an inherited condition such as a family history of cardiomyopathy or a genetic disorder such as fatty acid oxidation, Barth syndrome, or Noonan syndrome. Cardiomyopathy can also be a consequence of another disease or toxin where other organs are affected. Possible causes include viral infections (Coxsackie B - CVB), auto-immune diseases during pregnancy, the build-up of proteins in the heart muscle (amyloidosis), and an excess of iron in the heart (hemochromatosis). Excessive use of alcohol, contact with certain toxins, complications from AIDS, and the use of some therapeutic drugs (i.e. doxorubicin) to treat cancer can also contribute to the development of the disease.
Forms of Cardiomyopathy
There are four main types of nonischemic cardiomyopathy that are recognized by the World Health Organization: dilated (DCM), hypertrophic (HCM), restrictive (RCM) and arrhythmogenic right ventricular (ARVC). Each form is determined by the nature of muscle damage. With some patients, cardiomyopathy may be classified as more than one type or may change from one type to another over time. According to the pediatric cardiomyopathy survey, dilated cardiomyopathy is the most common (58%), followed by hypertrophic cardiomyopathy (30%) and a few cases of restrictive cardiomyopathy (5%) and arrhythmogenic right ventricular cardiomyopathy (5%). Although not formally categorized by the World Health Organization, left ventricular non-compaction cardiomyopathy (LVNC) is increasingly being recognized. With each type of cardiomyopathy, symptoms and reactions to pharmaceutical or surgical therapies may vary widely among patients.
Dilated Cardiomyopathy (DCM)Also known as congestive cardiomyopathy
This is the most common form of cardiomyopathy and it affects about 6 per million children each year. Dilated cardiomyopathy (DCM) occurs when disease affected muscle fibers are enlarged or stretched (dilated) in one or more chambers of the heart. Usually, the enlargement begins in one of the two lower pumping chambers (left ventricle) and then proceeds to the heart's upper chambers (atria) as the condition progresses. Eventually over time, all four of the heart's chambers are affected as the heart tries to "compensate" its weakened condition and poor contraction by further stretching. A possible complication is when the valves (mitral or tricuspid) between the upper chambers (atrium) and lower chambers (ventricles) also enlarge. As the heart enlarges, it decreases its efficiency in pumping blood through the body. When the disease progresses to congestive heart failure, fluid can build up in the lungs, liver, abdomen and lower legs.
DCM is usually an acquired condition in adults but with children most cases are idiopathic (unknown cause). Of those acquired cases, the disease can be caused by acute myocarditis an inflammation of the heart muscle from a viral infection. Commonly caused by a group of viruses called Coxsackie B viruses, the body's normal defense system (immune system) malfunctions, damaging heart tissues while attacking the invading virus. Other known causes are frequent use of certain drugs, excessive alcohol use, sensitivity to chemicals and toxins, infection due to HIV, build up of proteins in the heart muscle (amyloidosis), severe anemia or nutritional deficiencies and rare complications from pregnancy. Roughly 30% of cases are familial and genetic in nature.
Hypertrophic Cardiomyopathy (HCM)Also known as hypertrophic obstructive cardiomyopathy (HOCM), idiopathic hypertrophic subaortic stenosis (IHSS) and asymmetrical septal hypertrophy (ASH), non-obstructive hypertrophic cardiomyopathy (HCM)
The second most common form of heart muscle disease is hypertrophic cardiomyopathy. This disease is characterized by the abnormal growth and arrangement of muscle fibers in the heart (myocardial disarray), leading to excessive thickening of the heart walls. Typically, the portion of muscle mass that is thickest is in the heart's main pumping chamber (left ventricle) with the muscle wall that separates the heart's chambers (septum) affected most often. This condition is referred to as asymmetric septal hypertrophy. Although this is the more common form, the distribution of muscle thickness (hypertrophy), location, and degree of wall thickness may vary greatly among patients. Other forms of hypertrophy are symmetric ventricular hypertrophy (thickening is evenly distributed throughout the ventricle including the septum and wall) and apical hypertrophy (thickening is localized at the bottom portion of the heart).
In all three cases, the thickening of the muscle walls cause the heart chamber to be stiffer and smaller, making it difficult for blood to flow into and out of the heart effectively. This hypertrophy or thickening can progress to severe problems with obstruction of blood flow and relaxation of the left ventricle. Children with HCM are also at an increased risk of arrhythmias and sudden cardiac arrest. In advanced HCM (seen in less than 10% of patients), the disease may progress to a "dilated" form of cardiomyopathy where the heart muscle stretches to compensate for the enlarged muscle wall and poor pumping action.
HCM affects up to 500,000 people in the U.S. with children under 12 accounting for less than 10% of all cases. According to the Pediatric Cardiomyopathy Registry, HCM occurs at a rate of 5 per million children. The cause of HCM is largely unknown but most cases appear to be genetic in origin.
Restrictive Cardiomyopathy (RCM)
Restrictive cardiomyopathy (RCM) is the least common type of cardiomyopathy accounting for only 5% of patients with cardiomyopathy. It is especially rare in children. With this condition, the walls of the lower chambers of the heart (ventricles) have normal pumping function but abnormal relaxation. The ventricles become rigid and lose their flexibility to expand. As a result the upper chambers of the heart (atria) become enlarged while the lower pumping chambers (ventricles) remain normal in size. Eventually, the blood flow to the heart is restricted.
This condition in children is usually idiopathic, but with adults it typically results from another disease occurring elsewhere in the body. Known causes of RCM are build-up of proteins in the heart muscle (amyloidosis), excess iron in the heart (hemochromatosis), scarring of the heart from illness or open-heart surgery, chest exposure to radiation, and connective tissue diseases.
Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)Also known as arrhythmogenic right ventricular dysplasia, right ventricular dysplasia, right ventricular cardiomyopathy
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a very rare condition, and almost unheard of in children. With ARVD, heart muscle cells become disorganized and are replaced by fatty tissue. In the early stages of the disease, the right side of the heart may appear to be thickened in certain patches but later becomes dilated with a thinner wall. As the disease progresses, the muscles in the left portion of the heart are also reduced and thin layers of fat and fibrous tissue appear.
Tissue damage appears to be caused by a problem in the body's natural process to remove damaged cells. The body ends up killing its own healthy heart tissues and replacing it with fat. The disorganized structure of the heart leads to abnormal electrical activity (arrhythmias) and problems with the heart's contraction.
This condition usually presents in teens or early adults and is the most common cause of sudden death in athletes. It is believed to be an inherited disease with various forms of presentation.
Left Ventricular Non-Compaction Cardiomyopathy (LVNC)Also known as isolated non-compaction of the left ventricular myocardium or spongiform cardiomyopathy
Left ventricular non-compaction (LVNC) is a rare form of cardiomyopathy that is diagnosed by the presence of excessive deep grooves (trabecular recesses) in the muscle wall of the lower chambers (ventricles) of the heart. Both ventricles may be affected by the disease, but in most cases only the left ventricle is involved. It is thought that LVCM is caused by the abnormal embryonic development of the heart muscle. Early in gestational life, the heart starts as a "spongy" network of muscle fibers that gradually becomes compacted or compressed to develop normal coronary circulation.
With LVNC, the heart muscle appears to be a loose weave of fibers instead of a tight layer with all spaces removed. This appearance is described as "non-compaction" or "spongiform," and it can occur in the presence of normal heart function or in association with ventricular dysfunction where the heart muscle does not squeeze normally. When the ventricular function is below normal, it is called non-compaction cardiomyopathy, which can be associated with poor contraction and/or poor filling of the heart. When the heart function is found to be normal, the presence of non-compaction does not appear to be harmful. At this point, it is not known if non-compaction is an abnormality or if it is just a variation of "normal." Although there are concerns that the non-compaction pattern may evolve over time into non-compaction cardiomyopathy, it is not known how often this transition occurs and how often the ventricular function simply remains normal.
LVNC is estimated to affect about 1.2 per million children between 0-10 years of age. Similar to other forms of cardiomyopathy, it can be familial (genetic) or sporadic. There have been reports of specific gene mutations associated with LVNC, and the condition has been detected in patients who have generalized skeletal muscle weakness and other signs of neuromuscular or metabolic disorders.
General Complications From Cardiomyopathy
Several complications can occur with cardiomyopathies such as arrhythmias, heart block, blood clots, endocarditis, congestive heart failure and premature or sudden death. The most likely complications to occur in diagnosed children arrhythmias and congestive heart failure.
Many cardiomyopathies affect the heart's normal electrical impulses generating irregular heartbeats. With prolonged arrhythmias, the heartbeat may become either too fast (tachycardia) or too slow (bradycardia) and can occur in either the heart ventricles or atrial. If tachycardias are not treated they can become fibrillations which can be life threatening. Ventricular fibrillation is the most common arrhythmia associated with cardiomyopathy in children. With fibrillations, the regular rhythm of the heartbeat is lost and replaced by a chaotic, rapid heartbeat. This abrupt loss of organized heart function leads to insufficient blood being pumped to the body.
A very slow heart rate (bradycardia) can also occur when there is a problem in transmitting the electrical signal to contract the heart. If the heart's pumping ability is severely reduced, an artificial pacemaker may be needed.
About 10% of patients with hypertrophic cardiomyopathy develop arrhythmias. Patients with arrhythmogenic right ventricular and dilated cardiomyopathy are also susceptible but to a lesser degree. Early identification of high-risk patients allows for early treatment with anti-arrhymic medications or an implantable pacemaker/defibrillator to prevent sudden cardiac arrest.
If the normal electrical system within the heart fails to function properly, the heart's conduction is disrupted and the heartbeat may become too slow. If this occurs, a pacemaker needs to be implanted.
With dilated cardiomyopathy, the blood flow through the heart is abnormal which may cause blood clots to form within the heart (thromboembolism). Blood clots can damage other organs including the lungs and brain.
Children with cardiomyopathies or who have had heart surgery are more susceptible to endocarditis. This is an infection of the heart walls, valves or blood vessels caused by bacteria entering the blood stream. It typically occurs after a dental procedure or surgical procedures involving the gastrointestinal or urinary tract. Infection can lead to serious illness, additional heart damage and even death in rare instances. Taking prophylactic antibiotics (amoxicillin, erythromycin) before any dental or surgical procedures can help prevent endocarditis.
Congestive Heart Failure
This is a common feature of all late stage cardiomyopathies when the muscles of the heart become too weak to pump enough blood to the body for normal function. When this happens, fluid can build up in the lungs or in the rest of the body, causing difficulties in breathing, swelling, poor appetite, exercise intolerance and gastro-intestinal distress.
Premature Or Sudden Death
Sudden death is not as common in children with dilated cardiomyopathy. On the other hand, children with hypertrophic or restrictive cardiomyopathy are at a great risk of cardiac arrest occurring with little or no warning. Sudden death can be caused by several factors related to arrhythmia (i.e. ventricular tachycardia), myocardial ischemia, outflow obstruction, and intense physical activity.