Dilated Cardiomyopathy (DCM) in Dogs & Cats

Understanding Your Pet's Heart Condition

Dilated cardiomyopathy (DCM) is a disease of the heart that has two main components. The word "dilated" indicates that the main pumping chambers of the heart (the ventricles) are enlarged compared to their normal size. "Cardiomyopathy" refers generically to an abnormality of the heart muscle. In the case of DCM, the problem is that the muscle becomes weak and incapable of pumping blood forward as strongly as it should. DCM is an acquired type of heart disease and typically begins well into adulthood, as opposed to congenital heart disease which is present at birth.

DCM in Dogs

Although genetic transmission is suspected in many cases, it is not typically manifested until young adult or middle age. Genetic DCM can occur in any dog, although it is more commonly seen in large and giant breed dogs, such as Doberman Pinschers, Great Danes, and Irish Wolfhounds. Non-genetic, or secondary DCM, can also occur. Causes for this form of DCM include dietary deficiencies (e.g. the amino acid taurine), certain infectious diseases, etc. Grain-free and boutique diets have also been shown to have a correlation with the development of a secondary DCM.

DCM in Cats

In a small percentage of cats, it is caused by a dietary deficiency in taurine. Prior to the discovery of this problem in 1987, this was the most common cause of DCM in cats. Since then, however, feline diets have been formulated to contain adequate quantities of taurine, so that DCM caused by taurine deficiency is now rare. At least one study suggests a possible hereditary basis for DCM in some cats. Nonetheless, the majority of cases of DCM in cats are considered to be idiopathic, which means that no specific cause can be identified.

How Will My Veterinarian Diagnose DCM?

Prior to the onset of any symptoms, many dogs that develop DCM experience a protracted initial period during which there are no outward signs of disease. This period may last for months or even years, and has been variably designated "occult" or "pre-clinical" cardiomyopathy. Although symptoms are absent, diagnostic testing performed during this time may reveal the presence of arrhythmias as well as early or even more advanced structural changes (e.g. enlargement of heart chambers) typical of DCM.

What Your Veterinarian May Find During Examination

Abnormalities that may be noted during physical examination include the presence of a heart murmur (an abnormal "whooshing" sound associated with the normally crisp heart sounds) and weak pulses. An arrhythmia (irregular heart rhythm) may also be detected. Coughing may have been noted in the past, as well as during examination. If congestive heart failure is present at the time of diagnosis, other findings may include noisy breath sounds, increased respiratory rate or effort, abdominal distension, and weakness. Collapsing, typically due to arrhythmias, can also occur.

Tests Your Pet Will Need

Definitive diagnosis of DCM requires an echocardiogram (ultrasound examination of the heart). During this test, the size of the heart's chambers and the strength with which the heart contracts are measured. Dogs and cats with DCM have enlarged heart chambers and decreased contractile/squeezing cardiac function. In some dogs and cats, the chambers on the left side of the heart are predominantly affected (the left atrium and left ventricle), while in many others all four chambers are enlarged. The degree to which the pumping ability of the heart is decreased is variable. All of the above abnormalities tend to progress over time.

Other diagnostic tests are important during initial and followup evaluation. Chest x-rays provide a "big picture" view of the heart and lungs, and are used to assess the presence and severity of congestive heart failure. An electrocardiogram is performed to identify and characterize arrhythmias, and to guide antiarrhythmic therapy if necessary. Blood work and urine analysis are important in the assessment of organ function, particularly that of the kidneys. Kidney values and electrolytes can be affected by the medications used in the treatment of heart disease and heart failure. It is important to monitor these values so that side effects can be avoided or minimized. For some breeds of dogs, genetic testing is available. These tests can help to determine if an individual is more at risk for developing DCM.

Treatment Options for Your Pet

Unfortunately, there is no cure for most cases of DCM and the disease is typically progressive. The primary therapy for treatment of DCM is a medication called pimobendan (aka Vetmedin). This is a drug that improves the squeezing/contractile function of the heart without requiring the heart muscle to work harder. Pimobendan has been demonstrated to improve survival in dogs with DCM, both those that are asymptomatic as well as those with congestive heart failure.

ACE inhibitors are also often used, an example of which is the drug benazepril. ACE inhibitors cause blood vessels throughout the body to relax, creating more space within them for fluid. In addition, they help to combat some of the counterproductive hormonal processes that occur as a result of poor cardiac function. The goal of therapy with ACE inhibitors is to reduce the workload placed on the heart.

If congestive heart failure (fluid buildup due to poor cardiac function) is present or develops after initial diagnosis, furosemide (often referred to by one of its brand names, Lasix) is begun. Lasix increases urine production and so decreases the amount of fluid retained in the body. Similarly to ACE inhibitors, Lasix reduces the amount of work required by the failing heart.

If dietary factors are suspected to have caused or contributed to the development of DCM, diet changes and/or supplementation with nutrients such as taurine may be indicated. Other therapies, such as medications to control abnormal heart rhythms (antiarrhythmics) can be required in some cases.

What to Expect: Prognosis and Quality of Life

Prognosis for Dogs with DCM

Prognosis is extremely variable and depends upon whether or not congestive heart failure is already present at the time of initial diagnosis. If there is no evidence of heart failure, the time until it occurs is difficult to predict, but may be a year or more. Unfortunately, once heart failure occurs, long-term prognosis is poor, with average survival time ranging from a few to several months. However, medical therapy is useful to relieve symptoms of heart failure, and can often greatly improve overall quality of life during this time.

What to Watch For in Dogs

Symptoms that may be observed prior to the onset of congestive heart failure include coughing, intolerance to activity or exercise, lethargy, weakness, and fainting or collapse. If heart failure develops, symptoms may include the above as well as rapid or labored breathing. Potential side effects of medications used to treat DCM and heart failure overlap with those already mentioned and include lethargy, weakness, and loss of appetite.

If any of the above symptoms are noted, or if you have any questions or concerns, please call your veterinarian immediately to discuss an appropriate plan. Problems that are caught early are more easily corrected and less likely to require a visit to the hospital. If you feel that the problem should not wait and requires immediate attention, then an emergency visit is warranted.

Prognosis for Cats with DCM

Prognosis is variable between cats. Rare cases of taurine deficiency carry an excellent prognosis provided that heart failure, if present, is successfully resolved. For the majority of cats, prognosis depends upon whether or not congestive heart failure is already present at the time of initial diagnosis. If there is no evidence of heart failure, the time until it develops is difficult to predict but may be several months or more. Unfortunately, once heart failure occurs, long-term prognosis is poor. However, medical therapy is useful to relieve symptoms of heart failure, and can greatly improve quality of life during this time.

What to Watch For in Cats

Once the diagnosis of DCM has been made, it is important to watch for signs of congestive heart failure. Symptoms of heart failure include lethargy, weakness, intolerance to activity or exercise, and rapid or labored breathing. Some cats may only show mild behavioral changes such as hiding or loss of appetite. Finally, a small subset of cats with heart disease form blood clots inside their heart, which can then be released and become lodged in an artery downstream. This can result in a sudden onset of difficulty walking, atypical vocalization, and even sudden death.

Observation of even the milder of these symptoms warrants a phone call to your regular veterinarian. More severe symptoms, such as difficulty breathing or walking, require immediate attention on an emergency basis.

Moving Forward: Managing DCM Together

A diagnosis of dilated cardiomyopathy is serious, and it's natural to feel worried about your pet's future. While DCM is a progressive disease and the prognosis after heart failure develops is guarded, many pets experience significant quality of life improvements with appropriate treatment. The medications available today—particularly pimobendan, which has proven survival benefits—can help your pet feel more comfortable during their time with you. Early detection, particularly during the "silent phase" before symptoms appear, gives you and your veterinarian the best opportunity to monitor disease progression and begin treatment at the right time. If dietary factors contributed to your pet's DCM, diet changes may help. Stay in close communication with your veterinary team, watch for changes in your pet's breathing, energy, and appetite, and don't hesitate to call if you notice anything concerning. Your vigilance and partnership with your veterinarian make a real difference in your pet's comfort and wellbeing.