In dilated cardiomyopathy,
the heart muscle weakens and the heart becomes enlarged. As the heart becomes stretched, its lower chambers (the ventricles
) are less able to pump blood efficiently. Eventually, the heart is not able to pump enough blood to the body, and the lungs become congested. This condition is called heart failure
. Abnormal heart rhythms
may also result when the heart becomes enlarged.
Dilated cardiomyopathy can have several causes. One of the most common situations is after a viral infection that results in inflammation of the heart (myocarditis). In response to the infection, the body turns against its own heart muscle. It is not known why the viral infection affects the hearts of some people but not most others. Some babies may be born with a weak heart due to an illness suffered by the mother. Some people with muscular dystrophy or mitochondrial disorders may develop progressive weakening of the heart. Routine cardiac evaluation is necessary to detect this decline in heart function since symptoms may develop later, after the heart is severely weakened. Exposure to toxins, such as some kinds of chemotherapy used to treat cancers, can also result in dilated cardiomyopathy. Sometimes this becomes evident years after the treatment has occurred. While not as common in children, HIV infection can also result in dilated cardiomyopathy.
Symptoms of Dilated Cardiomyopathy
When the left ventricle is enlarged and unable to pump enough blood to the body, the body reacts by reducing blood flow to parts of the body. This leads to symptoms that can include:
- Pallor: The skin may appear more pale than usual because the blood vessels close to the skin's surface constrict in order to allow blood to preferentially go to the vital organs.
- Fast heart rate: The heart beats faster in its attempt to deliver more blood to the body.
- Arrhythmia: The sick heart may create abnormal heart rhythms, some of which may be life threatening.
- Shortness of breath with exertion/fatigue: As the heart’s lower left chamber (left ventricle) fails to pump blood out to the body effectively, proper flow of blood through the other heart chambers and the blood vessels from the lungs to the heart is restricted. One result can be a build-up of fluid in the lungs, which can make oxygenation more difficult. The skin may become cool and wet due to sweating (diaphoretic).
- Poor appetite and failure to grow properly: Because of the extra calories used by the heart and body to struggle to maintain proper blood flow, growth may be affected, particularly in babies.
Progression and Possible Complications of Dilated Cardiomyopathy
If cardiomyopathy is caused by a virus, it may improve on its own. Medications may help the heart undergo this healing process. If it does, the child can lead a normal life thereafter. It is believed that about one-third of patients with dilated cardiomyopathy get better, one-third stay the same with reduced heart function, and the condition severely deteriorates in about one-third of patients. Cardiomyopathy related to muscular dystrophy or a metabolic cause generally is progressive. Once cardiomyopathy becomes evident after chemotherapy treatment for cancer, it is also usually progressive.
In addition to reducing the heart’s ability to deliver sufficient blood to the body, the stretched and scarred heart muscles caused by cardiomyopathy may lead to abnormal heart rhythms, some of which may cause a life-threatening situation. Because of the sluggish blood flow created by the weakened pumping action of the heart, blood clots may develop within the heart. Blood clots are dangerous because they can break loose, travel through the bloodstream and lodge in the brain or lung, blocking blood flow and leading to stroke or death.
As the heart becomes enlarged, the valves may become stretched, resulting in leakage. This leakage can place additional strain on an already sick heart. Not only does the weak heart have difficulty pumping blood to the body, it may send blood backward through the valve that sends blood into the ventricle (the mitral valve).
As the heart becomes sicker, not only is the squeezing/pumping (systolic) action impaired, but the ability of the heart to relax in order to suck blood into it for the next pumping cycle suffers. This is called diastolic dysfunction. If leakage of the mitral valve worsens, this further impairs the ability of the heart to relax between pumping cycles. The heart becomes stiffer and blood backs up into the lungs. This results in congestion of the lungs and impairment of oxygenation of the blood. Furthermore, a back-up in blood pressure places additional stress on the lungs and can lead to the development of pulmonary hypertension.
Treatments for Dilated Cardiomyopathy
Medications commonly are prescribed to treat the congestive heart failure associated with dilated cardiomyopathy. These medications may include:
- Anti-inflammatory agents: In cases of suspected myocarditis, intravenous immunoglobulin (IVIG) - a concentrated preparation of antibodies - is commonly given shortly after the diagnosis is made to try to combat the immune reaction and inflammation. Steroids are sometimes given as well to try to quiet the immune response against the heart. However, these medicines do not always help
- Diuretics: These are medications that reduce the volume of blood in the body by increasing the need to urinate and eliminate fluids from the body. With less blood to pump, the burden on the heart is reduced. Diuretics, such as furosemide, are among the medications that help the body rid itself of excess fluids.
- Beta blockers: These medications are commonly used to reduce blood pressure. However, in the treatment of heart failure, these are used to blunt the body’s complex excessive adrenaline/hormone responses (neurohormonal response) that can actually make the heart failure worse.
- Afterload reducers: These medications allow blood to flow to the body and tissues easier. In oral form, these include ACE inhibitors (the names usually end in –pril) or angiotensin receptor blockers (ARB). In intravenous (IV) form, this may include milrinone.
- Inotropes: These help the heart to contract better. Digoxin is an oral medication that is sometimes used for sick hearts. In cases of severe heart dysfunction, intravenous (IV) medications given by a continuous infusion (such as milrinone or dobutamine) might be used.
Mechanical Heart Support
If the heart function continues to deteriorate to a critical level, medications alone may be insufficient. Mechanical measures to support heart function may be used as a bridge to heart transplantation. These are called ventricular assist devices. These devices are surgically attached to the heart itself. Some of these devices create pulsations similar to the natural heart. Others propel blood continuously and efficiently, though without pulsations. In adults, some of these devices can be placed within the body. However, due to the smaller body size of infants and children, these devices sometimes cannot be completely implanted within the body. In some situations, the patient may be placed on a machine called ECMO (extracorporeal membrane oxygenation). This is a heart–lung bypass machine that supports these organs completely. There are many risks associated with mechanical support of the heart, including severe infections and blood clots.
If the damage to the heart is considered to be permanent and unrecoverable, heart transplantation may be considered. However, currently the supply of donor hearts is much smaller compared to the number of people who might need them. The sickest patients are given the highest priority in receiving a transplanted heart. For many patients, this results in long waiting times for a heart to become available. Many people do not survive during this waiting period. The hearts must be matched to the patient regarding blood type and other immune markers. However, for some in early infancy, blood-type matching might not be necessary (ABO-incompatible transplant), since the baby's immune system may still be immature.
Heart transplantation is not a cure. A lifetime of continuous medical care is necessary due to the possibility of rejection of the transplanted heart. Numerous medications to suppress the immune system are necessary. This immune suppression may allow certain kinds of cancer to become more prevalent or infections to develop. The transplanted heart has a limited lifespan as well, likely due to chronic low-grade attack from the body. Coronary artery disease can be accelerated in transplant patients. Some people whose transplanted hearts have worn out may be able to receive another transplant; however, the lifespan of this heart is typically a fraction of the previously transplanted heart.