Dilated Cardiomyopathy

Overview

Dilated Cardiomyopathy is the most common cardiomyopathy in dogs, particularly in large and/or giant breed dogs. Dilated cardiomyopathy is rare in small and toy breed dogs (save for Cocker Spaniels), and occurs sparingly in cats. In dilated cardiomyopathy, the heart muscle becomes progressively weaker and larger (“flabby”). Most dogs are 4 to 10 years of age at time of diagnosis, and a majority of cases are found in male dogs (Eldredge, et. al., 2007). Doberman Pinschers are affected by DCM at a very high rate; it is important to have annual screening performed in these dogs. Other breeds are also overrepresented for the disease, including Newfoundlands, Great Danes, Irish Wolfhounds, Scottish Deerhounds, Boxers (especially European boxers) and some other large/giant breeds. DCM is rare in cats fed modern, taurine-supplemented cat foods; it may occur if an abnormal diet is fed (example – liver only). Rarely, cats on taurine-supplemented diets will be diagnosed with dilated cardiomyopathy; the prognosis is very poor in these cats, who often do not respond well to therapy.

There are many potential causes of cardiac enlargement and weakening. Strictly speaking, DCM is a disease of the heart muscle itself, which is also termed “idiopathic” DCM. This is known to be a genetic disease in some breeds, and is suspected to be genetic in others. Some breeds with a genetic or familial basis for DCM are Doberman Pinchers, Irish Wolfhounds, Cocker Spaniels, Newfoundlands, Boxers, and Great Danes; these breeds have a higher prevalence of DCM. In some dogs, deficiency of nutrients (especially Taurine) can result in DCM; this may be evaluated by blood tests. Other causes include infections (viral, parasitic, bacterial), shunts, chronic arrhythmias, toxin exposure, and infarction (“heart attack”, though rare in dogs). Your cardiologist can help work through which condition is present, and how best to evaluate the underlying cause.

Diagnosis

DCM can be difficult to diagnose, as many dogs with the disease have soft or inaudible heart murmurs, and clinical signs are often nonspecific until heart failure occurs. Nevertheless, a murmur or irregular heart beat auscultated by your veterinarian may be the first sign of DCM in a susceptible breed. Oftentimes this will prompt further investigation, including chest X-rays, ECG, and echocardiography. Chest X-rays will show the overall size of the heart, which is enlarged in dogs with late stages of DCM. It is also the ideal test for evaluating for heart failure, which will be evidenced by fluid in/around the lungs. ECG is a test of the electrical activity of the heart; it will allow diagnosis of an irregular heartbeat, and may help direct therapy and prognosis. Definitive diagnosis requires echocardiography (ultrasound of the heart); this will show the enlarged and weakened heart, as well as investigate for other diseases and complicating factors. Recently, some blood tests have become available (“biomarkers”) that help veterinarians with diagnosis and prognosis; these may be recommended in some cases.

Some screening tests are available to diagnose DCM before heart failure occurs. This is best performed in patient populations with a high prevalence of DCM, such as Doberman Pinchers. In Dobes, annual echocardiography is recommended starting at 2 years of age; this is between 95 to 100% effective in identifying “occult” or subclinical DCM if performed by an experienced echocardiographer (such as a veterinary cardiologist). Biomarker testing (blood tests) are generally less effective (but less expensive), although more information is currently being gathered. Genetic testing may become available in the near future.

Prognosis

Unfortunately, DCM is almost always progressive and terminal. The time frame in which that occurs, however, is widely variable and depends on the underlying cause. For example, nutritional DCM may resolve entirely with supplementation; idiopathic DCM in the Doberman Pinscher is fatal within weeks to months after the onset of heart failure. A cardiologist can help with your pet’s likely prognosis; however, there is no exact way to predict progression in each case.

There is no medication or intervention that is currently available to cure the disease. Some medications may be effective if started prior to the onset of CHF, but this decision is usually made on an individual basis. Once a dog has symptoms of CHF, however,* there are many medical options that are available to better the quality and quantity of life.* In humans, advanced DCM is most often treated surgically, via “assist devices” or transplantation. Unfortunately, this requires cardiopulmonary bypass, and is thus unavailable or cost-prohibitive in a majority of veterinary cases. Additionally, there has not been a study proving that surgery is better than medical management in dogs. Nevertheless, if you are interested in a surgical option, please ask a cardiologist for advice.

Symptoms

• rapid weight loss
• fainting attacks (syncope) – may look like a “seizure”
• crying out spells may be exhibited by cats
• lethargy
• rapid breathing when at rest / straining to take in air
• cold ears and feet, indicating poor circulation
• frequent coughing, sometimes bringing up bloody sputum, is a common sign of left-sided heart failure in both cats and dogs. The cough is usually dry, non-productive, and worse in the morning or during excitement.
• swollen abdomen (belly)

Treatment

• medication therapy aimed at decreasing fluid retention and correcting taurine deficiency
• restricted sodium and mineral diet – See Heart Disease: Resources: Diet