Cardiomyopathies occur more frequently in blacks than whites and more commonly in men than women. Factors that are associated with increased death rates in cardiomyopathy patients include the following:
Weak heart function (left ventricular ejection fraction:
- Aging (age greater than 55 years)
- Reduced functional capacity
- Electrical abnormalities
- Low blood sodium level (hyponatremia)
- Worsening kidney function.
The World Health Organization (WHO) classifies cardiomyopathy into 3 major groups:
- Dilated
- Hypertrophic
- Restrictive.
What are the features and causes of dilated cardiomyopathy (DCM)?Dilated cardiomyopathy (DCM) is typically characterized by significant enlargement of the 2 pumping chambers of the heart—the left ventricle (which pumps blood to the body) and the right ventricle (which pumps blood to the lungs). As a result of the chamber enlargement, there is some degree of reduction in the pumping power of the ventricle (reduced ejection fraction).
While there are many causes of DCM (nearly 80 specific diseases have been associated with DCM), a clear cause is often not identified in many individuals, and these cases are described as idiopathic. Alcohol abuse is a common cause of DCM, as long-term ingestion leads to cardiac cell (myocyte) damage with subsequent heart dysfunction. Many patients can see significant improvement if they stop drinking. Cocaine abuse can lead to DCM in some individuals; in 1 large study, more than 10% of cocaine users had at least mild left ventricular dysfunction.
Infectious causes can also lead to DCM. Viral infections can attack the heart muscle and lead to significant cardiac dysfunction; in many cases, the damage can be irreversible and severe. In young adults, severe viral-related DCM is the top reason to be "listed" for heart transplantation. Human immunodeficiency virus (HIV), the cause of AIDS, can also lead to DCM in a minority of causes. Vitamin deficiencies (such as thiamine) can lead to DCM, though such cases occur more commonly in Third World countries.
Metabolic disorders can lead to DCM. A relatively common example is hemochromatosis, a disease of iron metabolism, which is often familial and more common in men, in whom iron is deposited in the liver and heart muscle.
Peripartum cardiomyopathy is a form of DCM that typically occurs during the last 3 months of pregnancy and up to 6 months after delivery. It occurs in about 1 in every 5,000 pregnancies. The incidence is higher in women older than 30 years old and those with high blood pressure, multiple previous pregnancies, and twin pregnancies. Note that those who experience this condition are strongly discouraged from subsequent pregnancies, as the recurrence rate is high and death can even occur due to heart failure.
Chemotherapy drugs can lead to DCM in some individuals.
Drugs most commonly associated with DCM are doxorubicin, cyclophosphamide, amsacrine, and interferon. Neuromuscular disorders (disorders of the muscles and nervous system) are also associated with DCM.
Does therapy for DCM differ from that for congestive heart failure due to coronary artery disease (narrowing of the heart arteries)?
Treatment is similar for heart failure due to either DCM or coronary artery disease and includes:
- Salt restriction and diuretics (drugs that reduce lung and leg fluid via increased urine output)
- Beta-blockers (drugs that slow the heart rate and take stress off the heart)
- Angiotensin-converting enzyme (ACE) inhibitors (drugs that reduce the load on the heart by relaxing the body's major blood vessels)
- A combination of hydralazine and isosorbide nitrates (a drug option in those who cannot tolerate ACE inhibitors due to kidney function problems)
- Digoxin (a drug that helps improve the squeezing power of the heart).
What is hypertrophic cardiomyopathy (HCM)?Hypertrophic cardiomyopathy (HCM) is a primary disorder of the heart muscle characterized by inappropriate hypertrophy (excessive growth) of the left ventricle, which is the chamber that pumps blood to the body's organs and tissues. In many individuals, hypertrophy predominantly involves the septum, which is the intracardiac wall that separates the left ventricle and right ventricle.
In at least one-quarter of cases, this variant leads to obstruction of blood flow out of the left ventricle and into the aorta and, hence, is called hypertrophic obstructive cardiomyopathy (HOCM). Overall annual death rates in HCM individuals are approximately 3% per year in adults, while the rates are higher in those with HOCM.
What are the causes of hypertrophic cardiomyopathy (HCM)?In more than 50% of cases, HCM is genetically transmitted.
Most experts think that some if not all of the sporadic forms of HCM are due to spontaneous mutations (a sudden change in the genetic code of the developing fetus). At least 8 different genes have been associated with HCM. Note that genetic testing is not currently indicated (except in research settings), even in families in which HCM occurs, because knowing the type of gene defect does not impact subsequent treatment.
What are the most frequent symptoms in patients with HCM?Shortness of breath (dyspnea) occurs in approximately 90% of symptomatic individuals with HCM. It occurs due to a combination of abnormalities, including poor relaxation of the stiff, thickened heart muscle (diastolic dysfunction), reduced blood flow into the main heart pumping chamber (impaired ventricular filling), and increased pressures in the left atrium and pulmonary veins.
Fainting and near-fainting (syncope and near-syncope) can occur in HCM patients due to inadequate cardiac output during times of increased demand (such as physical exertion or severe stress). Serious arrhythmias can also result in fainting episodes; in fact, such arrhythmias are a top cause of sudden death in otherwise healthy children and young adults.
Chest pain (angina pectoris) occurs in up to three-fourths of symptomatic patients.The discomfort is a result of an imbalance between a reduced oxygen supply to the heart (because of thickened and narrowed heart arteries) and increased demand (due to greater heart muscle).
What noninvasive testing can be used to evaluate patients with suspected DCM or HCM?
Useful tests include electrocardiography (ECG), chest x-ray, and ultrasound (echocardiography).
In symptomatic individuals, the ECG is usually abnormal, but no specific findings are diagnostic of either DCM or HCM.
A chest x-ray will demonstrate an enlarged cardiac silhouette in DCM patients and in some HCM patients.
An echocardiogram provides the most useful and specific information. In DCM patients, severe dilatation of the ventricles is demonstrated, and an accurate estimation can be made of the impairment of heart function. In HCM patients, thickening of the left ventricle is the cardinal feature. Other findings include narrowing of the outflow tract through which blood flows from the left ventricle and out through the aortic valve and into the aorta, a small left ventricular cavity size, and abnormal motion of the mitral valve.
Beta-blockers (examples include metoprolol and atenolol), which are drugs that slow down the heart rate, are the cornerstone of medical therapy for HCM. In up to two-thirds of patients, they reduce the frequency of chest pain, shortness of breath, and near fainting.
What medical and invasive therapies are available to treat HCM patients?
Calcium channel blockers, such as verapamil, have also been utilized with good success; they appear to help the thick heart muscle relax better (decreased diastolic dysfunction) and can reduce the outflow tract obstruction.
Insertion of a pacemaker may be useful in some patients with an outflow gradient and severe symptoms.
In high-risk patients, especially in those who have had serious ventricular arrhythmias or aborted sudden death, an implantable cardiac defibrillator (ICD) should be inserted.
Surgical and invasive options exist for severely symptomatic patients. A surgical myomectomy, or excision of excess heart muscle, has a mortality rate of 3% or less in large centers. Surgery results in long-term improvement in symptoms and exercise capacity in most patients.
A nonsurgical invasive approach involves injection of alcohol into 1 of the arteries supplying the excessively thickened septal wall; this is done via left catheterization (a small incision is made in a leg or arm artery to allow delivery of a catheter into the specific artery under x-ray guidance). Short-term results in experienced centers have been promising, but long-term results are still not available.
What is restrictive cardiomyopathy (RCM), and what are the most common forms?
Restrictive cardiomyopathy (RCM)—the least common of the cardiomyopathies—is characterized by abnormal relaxation of the heart muscle in the presence of normal ejection fraction. RCM is often classified into myocardial (throughout the heart muscle) and endocardial (from inside the ventricle).
The most common myocardial forms are amyloidosis and sarcoidosis (infiltrative diseases); scleroderma or idiopathic (noninfiltrative diseases); and hemochromatosis, glycogen storage diseases, and Fabry's disease (storage diseases).
Infiltrative diseases refer to abnormal proteins and cells generated by certain disease states that penetrate the heart muscle. Noninfiltrative diseases are typically diseases related to activation of the autoimmune system or due to a genetic abnormality that activates abnormal cardiac muscle growth, where the storage diseases refer to genetic abnormalities that lead to abnormal storage of sugars and other substances inside the heart muscle cells.
The most common endocardial forms of RCM are carcinoid, metastatic malignancy (spread of cancer), and endomyocardial fibrosis.
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