Dilated cardiomyopathy (DCM) is an acquired disease of the heart muscle that is most often seen in large and giant breed dogs. It is characterized by a progressive decrease in the systolic function (contractility) of the heart, ultimately leading to dilation or enlargement of the cardiac chambers. It most often affects the left ventricle (the lower chamber on the left side of the heart), but may also affect the right ventricle. Over time the pressures within the heart can increase, and this increased pressure may then back up into the blood vessels in the lungs, allowing fluid to seep out of the vessels and into the air spaces of the lungs (pulmonary edema). When an animal has evidence of fluid in the lungs secondary to heart disease, this is called congestive heart failure. Other potential complications of DCM include hypotension (low blood pressure), arrhythmia (abnormal heart rhythm), syncope (“fainting”), and pulmonary hypertension (resistance to blood flowing to the lungs). Unfortunately, some dogs with DCM can suffer sudden death, which is thought in most cases to be due to an arrhythmia.
If an animal has DCM that is affecting the right side of the heart, the increased right-sided pressures are transmitted back up into the blood vessels (systemic veins) that drain into the right atrium. This increased pressure allows fluid to leak from the veins into the body cavities (into the space surrounding the lungs [pleural effusion], into the pericardial sac surrounding the heart [pericardial effusion] or into the abdomen [peritoneal effusion]) or underneath the skin. Significant pleural effusion will lead to difficulty breathing and can be life-threatening. Severe abdominal effusion can cause discomfort, decreased appetite, and may interfere with breathing by increasing pressure on the diaphragm. Additionally, animals with rightsided congestive heart failure often show progressive cachexia (muscle wasting). Right-sided congestive heart failure is usually managed with a combination of medications and manual removal of excess fluid when indicated.
Certain breeds or populations of dogs may develop DCM as a result of taurine and/or carnitine deficiency. Taurine deficiency has been suspected or documented in American cocker spaniels, golden retrievers, Labrador retrievers, Dalmatians, English bulldogs, Portuguese water dogs, dogs being fed a proteinrestricted diet long-term (i.e. for management of urinary stones), and dogs eating lamb meal and rice based dog food. Carnitine deficiency leading to DCM has been suspected or documented in Boxer dogs, American cocker spaniels and dogs with urinary system stones. Even if an animal is not deficient in these amino acids, there may be some clinical improvement when they are supplemented in dogs with DCM. In rare cases DCM may be secondary to a cardiac arrhythmia – a condition called tachycardia-induced cardiomyopathy. The only way to differentiate between primary DCM and tachycardia-induced cardiomyopathy is to assess for improvement in cardiac contractility (via a recheck echocardiogram) once the arrhythmia is controlled.
Treatment of DCM generally involves attempting to slow disease progression with medications, as well as managing clinical signs when they arise. Ultimately the goal is to provide your pet with the best quality of life for as long as possible. Unfortunately, definitive treatment options (such as heart transplants) are not available at this time in veterinary patients.
The short-term prognosis for mild to moderate DCM can be good with medications and monitoring. The long-term prognosis is dependent on how quickly the disease progresses. Unfortunately, the long-term prognosis for severe DCM with heart failure is poor. An individual animal’s prognosis is dependent on several factors, such as concurrent arrhythmia or pulmonary hypertension, as well as the presence of other diseases like chronic kidney disease.