Cardiomyopathy
Cardiomyopathy is a group of diseases that affect the heart muscle, leading to a range of symptoms and complications. It can be categorized into several types, including hypertrophic, dilated, and restrictive cardiomyopathy, each with distinct characteristics and causes. Genetic factors are significant in many cases, particularly for hypertrophic and dilated cardiomyopathy, where specific gene mutations can lead to abnormal heart muscle growth and function. Environmental risk factors also play a role, with conditions such as obesity, diabetes, and hypertension increasing the likelihood of developing cardiomyopathy.
Symptoms vary based on the type and severity of the condition, often including chest pain, shortness of breath, fatigue, and swelling in the legs. Diagnosis typically involves a comprehensive medical history, physical examination, and various tests such as echocardiograms and electrocardiograms to assess heart function. Treatment focuses on relieving symptoms and preventing further damage, employing lifestyle modifications, medications, and, in some cases, surgical interventions like pacemaker implantation or heart transplantation. Prevention strategies emphasize managing risk factors and obtaining regular health screenings, particularly for individuals with a family history of the disease.
Cardiomyopathy
DEFINITION Cardiomyopathy refers to heart muscle disease. The damaged heart does not effectively pump blood. The disease usually progresses to the point where patients develop life-threatening heart failure. In addition, patients with cardiomyopathy are more likely to have irregular heartbeats or arrhythmias.
There are two major categories of cardiomyopathy: ischemic and nonischemic cardiomyopathy. Ischemic cardiomyopathy occurs when the heart muscle is damaged from heart attacks due to coronary artery disease. Nonischemic cardiomyopathy, the less common category, includes types of cardiomyopathy that are not related to coronary artery disease. There are several different types of cardiomyopathy. In dilated cardiomyopathy—the most common form of the disease—damaged heart muscles are stretched and thinned, leading to an enlarged, floppy heart. The heart stretches as it tries to compensate for weakened pumping ability. In hypertrophic cardiomyopathy, heart muscle cells enlarge abnormally. The heart wall thickens, leaving less space for blood in the chambers and potentially blocking blood flow out of the heart chambers. In restrictive cardiomyopathy, portions of the heart wall become rigid and lose their flexibility. Thickening often occurs due to abnormal tissue, such as scar tissue, invading the heart muscle. The chambers of the heart subsequently become incapable of relaxing normally, leading the atria to become enlarged.
Risk Factors
Individuals whose family members have cardiomyopathy are at risk for the disease. Other risk factors include alcohol abuse or alcoholism, obesity, diabetes, hypertension, heart attack, coronary artery disease, and the use of certain drugs. Certain conditions can also damage the heart and cause cardiomyopathy, including hemochromatosis, sarcoidosis, and amyloidosis.
Etiology and Genetics
While there are several identifiable environmental factors that can trigger each of the various categories of cardiomyopathy, genetic factors play an important role as well, particularly in the cases of dilated, hypertrophic, and restrictive cardiomyopathy. In hypertrophic cardiomyopathy, the cardiac muscle fibers often show abnormal growth and arrangement as a result of mutations in any of several genes that encode protein components of sarcomeres, the contractile units of heart muscle.
Several genes have been identified in which mutations account for the majority of cases of familial hypertrophic cardiomyopathy. MYH7, found on the long arm of chromosome 14 at position 14q12, encodes the heavy chain of 7 of cardiac myosin; and MYBPC3, found on the short arm of chromosome 11 at position 11p11.2, specifies the cardiac myosin binding protein C. In both of these genes the inheritance pattern seems to be autosomal dominant, meaning that a single copy of the mutation is sufficient to cause full expression of the disease. An affected individual has a 50 percent chance of transmitting the mutation to each of his or her children. Many cases, however, result from a spontaneous new mutation, so in these instances affected individuals will have unaffected parents. Mutations in the genes TNNT2 and TNNI3 are also commonly implicated in cases of familial hypertrophic cardiomyopathy.
More than thirty genes have been shown to play a role in the development of dilated cardiomyopathy, particularly those genes that provide the instructions to make the proteins in cardiomyocytes, which help to form the cardiac muscles. Mutations in the gene TNNI3 are a significant cause of familial restrictive cardiomyopathy. TNNI3 encodes the instructions for making cardiac troponin I, which plays a role in contracting and relaxing the heart muscle.
Other genetic syndromes may include cardiomyopathy as one of many clinical manifestations. For example, Barth syndrome, a rare X-linked condition affecting male children in their first year of life, can include dilated cardiomyopathy. One type of hereditary hemochromatosis, a disease associated with abnormal iron absorption, can lead to restrictive cardiomyopathy, as well as additional abnormalities in the liver, pancreas, and pituitary gland.
Symptoms
Symptoms vary depending on the type of cardiomyopathy and its severity. Patients with hypertrophic cardiomyopathy may experience chest pain, dizziness, or shortness of breath; however, many do not notice any symptoms. Sudden cardiac death may be the first indication of the condition.
It may take years for symptoms of dilated cardiomyopathy to develop. Blood clots may form due to the abnormal pooling of blood in the heart. If a clot moves to another part of the body (embolism), symptoms associated with that organ (the brain, for example) may be the first sign of the heart disease.
Cardiomyopathy ultimately leads to heart failure and the following symptoms: fatigue; weakness; shortness of breath, often worse when lying down or with exertion; cough; swelling in the feet or legs; chest pain; and irregular heart rhythm.
Screening and Diagnosis
The doctor will ask about a patient’s symptoms and medical history and will perform a physical exam. The doctor will also listen to a patient’s heart with a stethoscope; cardiomyopathies often produce heart murmurs and other abnormal heart sounds.
Tests may include a chest X-ray to look for heart enlargement; an electrocardiogram, a test that records the heart’s activity by measuring electrical currents through the heart muscle; and an echocardiogram, a test that uses high-frequency sound waves (ultrasound) to examine the size, shape, and motion of the heart. Blood tests can check for damage to the heart and other organs and possibly the underlying cause or causes of the cardiomyopathy. Other tests include cardiac catheterization, in which a tube-like instrument is inserted into the heart through a vein or artery (usually in the arm or leg) in order to detect problems with the heart and its blood supply, and a heart biopsy, the removal of a sample of heart tissue for testing.
Treatment and Therapy
When heart failure is due to blockages in the coronary arteries, treatment directed at relieving these blockages through angioplasty, stent placement, or bypass surgery may lead to improvements in heart function and symptoms. For certain genetic causes, other treatments may also lead to improvements in function. For many patients, however, treatment is aimed at relieving symptoms and preventing further damage.
Lifestyle modification aims to eliminate anything that contributes to the disease or worsens symptoms. These lifestyle changes may include avoiding alcohol, reaching or maintaining a healthy weight, eating a low-fat diet to minimize the risk and extent of coronary artery disease, and limiting salt intake to decrease fluid retention and lower blood pressure. Patients should follow their doctors’ advice for exercise; they may need to limit their physical activity.
Medications for cardiomyopathy may include diuretics to eliminate extra fluid; ACE (angiotensin converting enzyme) inhibitors to help relax blood vessels, lower blood pressure, and decrease the heart’s workload; digitalis medications to slow and regulate the heart rate and modestly increase its force of contractions; and calcium channel blockers to lower blood pressure and relax the heart. Other medications include beta blockers to slow the heart and limit disease progression; antiarrhythmia agents to prevent irregular heart rhythms; and immune system suppressants, including steroids (depending on the underlying cause).
Surgical options include implanting a pacemaker to improve the heart rate and pattern. For patients with hypertrophic disease, doctors may remove part of the thickened wall separating the heart’s chambers. Surgery may also be needed to replace a heart valve.
A heart transplant may be possible for otherwise healthy patients who do not respond to medical treatment. Candidates often wait a long time for a new heart. Those waiting may temporarily receive a ventricular assist device—a mechanical pump that assumes some or most of the heart’s pumping function.
Prevention and Outcomes
Aggressively treating hypertension, coronary artery diseases, and their risk factors is the best way to prevent most cases of cardiomyopathy. Other, less common causes, however, are not preventable. Individuals with a family history of the disease should ask their doctors about screening tests, especially before starting an intense exercise program.
Bibliography
"Cardiomyopathy." MedlinePlus, NIH National Library of Medicine, 15 Nov. 2023, medlineplus.gov/cardiomyopathy.html. Accessed 17 Jan. 2025.
Domino, Frank J., et al., editors. Griffith’s Five-Minute Clinical Consult. 25th ed., Lippincott Williams & Wilkins, 2016.
Goroll, Allan H., and Albert G. Mulley, editors. Primary Care Medicine: Office Evaluation and Management of the Adult Patient. 7th ed., Wolters Kluwer, 2014.
"What Is Cardiomyopathy?" National Heart, Lung, and Blood Institute, US National Institutes of Health, 6 Dec. 2024, www.nhlbi.nih.gov/health/cardiomyopathy. Accessed 17 Jan. 2025.
"What Is Cardiomyopathy in Adults?" American Heart Association, 28 May 2024, www.heart.org/en/health-topics/cardiomyopathy/what-is-cardiomyopathy-in-adults. Accessed 17 Jan. 2025.