Types of Cardiomyopathy in Dogs

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Types of Cardiomyopathy in Dogs

Cardiomyopathy is a common heart disease in dogs. It includes any disorder that affects the muscles of the heart which can eventually lead to the heart losing its ability to pump blood efficiently. In some cases, arrhythmias (irregular heartbeats) can also be present in dogs with cardiomyopathy. The thickening of the heart muscles is brought about by an increase in the growth of muscle cells. Two types of cardiomyopathy can affect dogs - dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). Continue reading to learn more. 

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Dilated Cardiomyopathy (DCM) in Dogs

Of the two types of cardiomyopathy in dogs, DCM appears to be the most common. It’s thought to be an inherited defect and mainly affects certain large and giant breed dogs, such as Afghan hounds, Doberman Pinschers, Boxers, Irish Wolfhounds, St. Bernards, Airedale Terriers, and Portuguese Water Dogs, to name a few. Male dogs appear to be more prone to developing the condition. Small dog breeds can develop DCM but cases are rare.

With dilated cardiomyopathy, the degeneration of the heart muscles causes them to become thinner. The pressure of the blood inside the dog’s heart causes stretching of the heart’s thin walls leading to a much larger heart (dilation). The normally thick wall of the left ventricle is usually the one that becomes most affected but dilatation of all the four chambers of the heart has also been observed in many cases of DCM in dogs. The dilation can prevent the heart from pumping enough blood and oxygen to the body which can eventually lead to congestive heart failure or death.

With DCM, the opening of the heart valves between chambers also becomes larger which can lead to backflow of blood from the ventricle to the atrium.

Causes of Dilated Cardiomyopathy in Dogs

According to the Cornell University College of Veterinary Medicine, the definitive cause of canine DCM is a subject of debate, although many factors including nutritional, infectious, and genetic predisposition have been implicated. Dietary carnitine deficiency may play a role in some cases of Boxer DCM, and taurine responsive DCM has been identified in Cocker Spaniels.

Some systemic conditions that can contribute to the development of DCM in dogs include hypothyroidism, myocarditis, prolonged tachycardia (increased heart rate), and poor blood flow to the heart muscles.

Signs of Dilated Cardiomyopathy in Dogs

The symptoms of DCM occur as a result of the heart’s diminished capacity to deliver enough oxygenated blood to the body or because of blood congestion in the lungs.

  • Poor tolerance to exercise and other forms of physical activity
  • General slowing down (weakness and lethargy)
  • Rapid breathing while at rest or sleeping
  • The dog’s feet feel cool to the touch
  • Coughing
  • Decreased appetite
  • Weight loss
  • Pot-bellied appearance
  • Difficulty (labored) breathing*
  • Blue-tongue*
  • Excessive drooling*
  • Collapse*
  • Sudden death

* If your dog is showing these signs, you should seek veterinary attention immediately.

The symptoms of DCM may appear to have a sudden onset, but in reality, the problem has been gradually progressing. The early signs can be so subtle that the pet owner fails to notice there is something wrong.

The dilation of the heart muscles, decrease in the supply of oxygen in the body, coupled with increased oxygen demand are important predisposing factors to the development of cardiac arrhythmias that may occur in the atria (atrial fibrillation) or ventricles (ventricular tachycardia). Arrhythmia can be an important predisposing factor for sudden death in dogs with DCM.

Prevention and Treatment of DCM in Dogs

There is no effective way to prevent the development of DCM in dogs. Treatment regimens are not curative but are geared toward improving the affected dog’s quality of life, slowing down the onset of heart failure symptoms, and improving life expectancy. Most dogs diagnosed with DCM eventually succumb to the disease.

Hypertrophic Cardiomyopathy in Dogs

Hypertrophic cardiomyopathy (HCM) is a rare disease that can affect the heart muscles. Dogs with HCM have heart walls that are thicker than normal. The walls of the left ventricle become excessively thick over time which can affect the heart’s ability to pump adequate quantities of blood throughout the body during contraction.

The cause of HCM in dogs has not been established but genetic abnormalities can be a potential culprit. More cases of HCM are diagnosed in male dogs younger than three years old. There is also a higher risk observed in adult Boston Terriers.

In severe HCM, muscles cells can die and eventually lead to scarring and accumulation of fibrous tissue. The thick and fibrous heart muscle causes pressure buildup within the heart and affected dogs can end up with left-sided heart failure and/or a stroke caused by a blood clot.

Symptoms of Hypertrophic Cardiomyopathy in Dogs

Most dogs that are affected with HCM are asymptomatic (don’t show any symptoms). The symptoms that are exhibited by symptomatic dogs are associated with congestive heart failure. Because many cases are asymptomatic, most dogs with HCM are often brought to the attention of a veterinarian as a result of sudden heart failure that is usually fatal.

How are cardiomyopathies diagnosed in dogs?
If cardiomyopathy is suspected, your vet will perform several diagnostic tests that will include:

Physical exam and auscultation - Using a stethoscope, your vet will listen to your dog’s heart for abnormal sounds, such as murmurs, which can indicate improper closure of the heart valves. This will also enable your vet to determine the location and intensity of the murmur. Chest auscultation (listening to the chest with a stethoscope) also includes assessment of heart rhythm and evaluation of the lungs.

Blood tests and urinalysis - In the presence of heart disease, liver and kidney function can be compromised. These tests can help determine if any issues are affecting the structure and function of these important organs.

ProBNP - This is a type of blood test that measures the level of a specific protein in the body that can be affected when there are changes to the heart structure and heart disease.

Chest x-rays (radiographs) - Chest radiographs can provide valuable information about the size and shape of the heart. If DCM is present, there is a distinct heart enlargement that is more prominent on the left side.

Electrocardiogram (ECG) - The procedure evaluates the electrical activity of the heart and allows the accurate determination of the heart rate and detection of abnormal heart rhythms.

Echocardiogram - This is a special ultrasound of the heart that provides accurate information regarding the size of the heart chambers and the thickness of the heart’s walls. Heart contractions can also be measured to evaluate the pumping efficiency of the heart.

Holter Monitor - This is a portable ECG device that the dog has to wear for 24-48 hours. It can record the heart rhythm which can help determine the presence of irregular heartbeats (arrhythmias).

What to Expect if Your Dog has Cardiomyopathy

The prognosis for dogs diagnosed with DCM is highly variable and will depend on the breed and status at the time of diagnosis. Doberman Pinschers with DCM have a less favorable prognosis compared with other dog breeds. On the other hand, the prognosis in Cocker Spaniels with DCM can be slightly favorable because it’s generally slowly progressive. If congestive heart failure is already present, the prognosis is generally poor.

As for HCM, the prognosis is extremely variable. Some medications can help address and alleviate symptoms and abnormalities but they’re not a cure. Sudden death and the development of congestive heart failure can occur.

Read more:

Your Pet’s Heart: A Guide to Understanding Heart Health in Dogs and Cats

Grain-Free Diets for Pets: Separating Facts from Fiction

Can cats develop heart disease?

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Published: 12/10/2021

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