In a properly working heart, blood flows into the right atrium and is pumped into the right ventricle. After that, it goes to the lungs where it picks up oxygen and then flows back into the heart’s left atrium. Pressure causes the oxygenated blood to flow into the left ventricle and out of the heart via the aorta. Dilated Cardiomyopathy (DCM) is a disease that affects heart tissue. Usually one or even both ventricles are affected. This prevents the heart from pumping blood through the dog’s heart and out into the body properly. Because the heart has to work harder, it becomes enlarged. At the same time, the chamber walls of the heart become very thin and weakened. This, in turn, affects the heart’s output. All parts of the body are affected when the heart doesn’t work properly, since each organ or system gets less oxygen than it needs. The kidneys and lungs are particularly vulnerable to damage caused by DCM. Many times, Dilated Cardiomyopathy is accompanied by arrhythmias and/or congestive heart failure (CHF). DCM is a common cause of CHF in giant and large breed dogs. Typically, dogs begin to show signs when they are between four and six years of age.
This disease is what vets and doctors call “idiopathic” – no one knows for sure what causes it. Many things may contribute to DCM, such as viral infections, genetic disorders, malnutrition that involves deficiency in taurine and/or carnitine, microvascular hyperactivity, immune-mediated abnormalities, exposure to toxins, hypothyroidism, myocarditis, bacterial infections, and protozoal infections.
Because there is no known cause, there really is no way to prevent a dog from developing Dilated Cardiomyopathy. Dogs that are affected should be removed from breeding programs, and parents of dogs with the disease should not be bred again to each other, in case it is hereditary. Some breeders go further and suggest that even littermates of affected dogs should be kept from breeding, even if they have not developed the disease themselves.
Many dogs with early stages of the disease will show no signs of illness – this is called preclinical DCM. Once the disease progresses to a point where it becomes clinical (symptoms are present), the dog usually will exhibit symptoms similar to those for cardiac arrhythmias and congestive heart failure. The most obvious sign is respiratory difficulty that range from uncomfortable to extremely painful. Other symptoms include vomiting, heart murmur, tachypnea, abnormal lung sounds, weakness, nasal discharge, depression, distended or swollen abdomen, coughing (especially at night), lack of appetite, fainting, weight loss, exercise intolerance, and sudden death. Usually, by the time a dog shows signs of DCM, it has only six months to a year left of life.
Dogs at Risk
Dogs at the highest risk of developing Dilated Cardiomyopathy are of middle age, and are large or giant size. Breeds most prone are Doberman Pinschers, Boxers, Scottish Deerhounds, Golden Retrievers, Afghan Hounds, Irish Wolfhounds, Great Danes, Portuguese Water Dogs, Old English Sheepdogs, Schnauzers, Burmese Mountain Dogs, Newfoundlands, Saint Bernards, Springer Spaniels, and Cocker Spaniels. The disease appears to be more prevalent in males than females.
No one knows why, but Doberman Pinschers seem to develop this disease more than all other breeds combined. They will often display signs of abnormal heart function for up to four years before they show signs of heart failure. Many simply die suddenly without even showing any signs of illness.
Boxers that develop the disease will have abnormal heart rhythms but no other signs of the illness. These dogs are also more likely to suddenly collapse, or have fainting spells.
Testing and Diagnosis
Unfortunately, many cases of DCM go undiagnosed until it is in the late stages. Sometimes it is found during a routine exam, or when the vet does x-rays for an unrelated reason and sees that the heart is enlarged.
If this disease is suspected, the vet may order chest x-rays to look for signs of pulmonary edema and/or pleural effusion. The dog’s liver may also appear enlarged. The standard for diagnosing DCM is echocardiography. This is an ultrasound of the heart, and is usually done at specialised centres and vet training facilities since most general veterinarians don’t have this equipment. The echocardiogram can show enlargement, abnormal blood flow, and arrhythmias.
Treatment and Prognosis
Alleviating fluid build-up in the abdomen, chest, or lungs and resolving any signs of congestive heart failure, improving heart muscle contraction force, controlling irregular heart rhythms that are life-threatening, and improving the dog’s overall quality of life are the therapeutic goals for dogs with Dilated Cardiomyopathy. There is no cure for DCM, and it is most often fatal within six to 24 months of diagnosis.
Acute respiratory distress can be treated with oxygen. These dogs should be kept in a quiet, warm environment and IV fluids will correct fluid or electrolyte balances as needed. Diuretic medications may relieve pulmonary edema or pleural effusion. The vet may drain fluid from the chest cavity but this is a highly invasive procedure. Many different drugs may be used to regulate and stabilize heart contractility, function, and activity.
Dogs diagnosed with DCM should be allowed to select their own level of activity. They should be fed a low-sodium diet. Other treatment options should be discussed between owner(s) and vet.