Dilated Cardiomyopathy

What is dilated cardiomyopathy?

Dilated cardiomyopathy (DCM) is a disease affecting the muscle of the heart and is most commonly seen in medium to large-breed dogs. Dobermans, Great Danes, Boxers, Wolfhounds, and Cocker Spaniels are predisposed, though DCM can also rarely be seen in small dogs and cats. Dilated cardiomyopathy can occur due to a primary abnormality of the heart muscle itself, but can also be seen secondary to diet, abnormal heart rhythms, infectious causes or metabolic diseases. The overall effect of DCM is a decrease in the contractility (pumping ability) of the heart.

What are the consequences of DCM?

Because the heart is unable to pump strongly enough to move blood forward into circulation, it becomes overloaded and starts to stretch out. As a result, the chambers of the heart become large. Ultimately, if the heart is unable to stretch any further, fluid can back up from the heart into the lungs, known as congestive heart failure (“fluid on the lungs”).

The changes in the muscle of the heart in dogs with DCM (scar tissue formation and stretching of the heart chambers) can lead to the development of abnormal heart rhythms (arrhythmias). Common arrhythmias with DCM include atrial fibrillation, which is a fast and chaotic rhythm originating from the top of the heart. Because of the rapid and irregular nature of this rhythm, it can further worsen pumping ability of the heart and cause the onset of congestive heart failure. Unfortunately, dogs with DCM are also prone to life-threatening arrhythmias originating from the bottom of the heart (ventricular tachycardia).

How is DCM diagnosed?

Diagnosis of DCM is made with an echocardiogram (ultrasound of the heart) by a veterinary cardiologist. Following initial diagnosis, regular checkups are recommended to monitor progression and start medications if needed. If heart failure is suspected, chest x-rays will also be recommended to look for fluid in the lungs.

Additional blood tests including thyroid testing and cardiac biomarkers are sometimes recommended. If abnormal heart rhythms are present, ECG or Holter monitoring (24-hour ECG vests) are performed.

For breeds predisposed to DCM, annual screening is recommended. For example, the European Society of Veterinary Cardiology recommends Dobermans are screened for DCM annually starting at three years of age with an echocardiogram and Holter monitor. Genetic testing is available for Dobermans and Great Danes. Please remember that genetic tests can help quantify risk or aid in breeding programs, but some dogs who test negative for the affected gene go on to develop DCM and vice versa.

What are the symptoms of DCM?

Many dogs with mild forms of DCM do not have any symptoms, and it is important to remember that not all dogs with this disease will progress to experience complications. However, dogs with DCM can experience symptoms of heart failure (increased breathing rate or effort, cough, distended abdomen), decreased energy level or exercise ability, or decreased appetite. If abnormal heart rhythms are present, fainting can occur. Unfortunately, sudden death can be the first sign of disease in some cases.

How is DCM treated?

Before the development of heart enlargement, no treatment is necessary. Once the heart enlarges, treatment with pimobendan has been shown to delay the onset of heart failure in dogs with DCM. If symptoms of heart failure are present, treatment with diuretics +/- additional drugs to reduce scar tissue formation, control abnormal rhythms, or supplement electrolytes may be added.

If dietary, metabolic or infectious causes are suspected, diet change or additional medications may be used. Finally, in addition to drug therapy, nutritional supplements are sometimes recommended.

How should I care for my dog with DCM at home?

Before the onset of heart failure, most dogs can live normally with no restrictions. Special diets are not required, though very salty foods (human foods, jerky treats) should be avoided. We advise dogs to avoid grain-free diets or diets high in legumes (lentils, peas, chickpeas, beans etc should not be included in the top ten ingredients) as these diets have been associated with the development of DCM in dogs.

Dogs with DCM should be monitored for symptoms of worsening heart disease listed above. If these signs are noted, please contact a veterinarian. We will also ask you to monitor your dog’s sleeping breathing rate at home. A normal breathing rate (while sleeping) is less than 36 breaths/minute. There are apps available that can help you count and track this rate at home.

What is the prognosis with DCM?

Dogs with DCM that are asymptomatic (termed occult DCM) often do well for many years, though the average time to development of symptoms varies (1-4 years). Unfortunately, sudden death remains possible for asymptomatic dogs, especially for Dobermans. After the onset of heart failure, with medications, most dogs continue to have an excellent quality of life and can often live 6-12 months, though survival time varies widely between dogs. For dietary DCM, a diet change can sometimes reverse changes to the heart, and the prognosis may be more favourable.