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Cardiomyopathy, Hypertrophic in Dogs

Hypertrophic cardiomyopathy (HCM) is a rare form of heart muscle disease in dogs. It is characterized by a thickening of the walls of the heart, which leads to an inadequate amount of blood being pumped out into the body when the heart contracts during the systolic phase (pushing blood out into the arteries). When the heart relaxes between contractions during the diastolic phase (taking blood in from the vessels), an insufficient amount of blood will fill the chambers of the heart. Ultimately, HCM often will lead to congestive heart failure.

This disease, although extremely rare to dogs, usually affects young male dogs that are younger than three years old. There is also a higher incidence of the disease in mature Boston Terriers.

Symptoms and Types

Most dogs with HCM will not exhibit any symptoms of the disease. If your dog is symptomatic, it will exhibit signs of congestive heart failure. These include exercise intolerance, shortness of breath, coughing, and a bluish discoloration of the skin. Very rarely, a dog with HCM may experience a transient loss of consciousness, or fainting, during a high level of activity or exercise. During a physical veterinary examination, a dog with HCM may exhibit systolic heart murmur, and a heart gallop. Unfortunately, in most cases, the most commonly reported clinical sign of HCM is sudden, fatal heart failure.

Causes

The cause of HCM in dogs is largely unknown. Although some genetic abnormalities in gene codings for certain proteins have been detected in humans and cats with the disease, no such evidence exists for dogs.

Diagnosis

Diagnosis of HCM through medical tests is relatively difficult and involves a number of procedures. Radiographic findings may either return normal results, or may show an enlargement of the left ventricular and atrium. If a dog with HCM has left-sided congestive heart failure, there will be a buildup of fluid in the lungs. An electrocardiogram (EKG) will typically reveal normal results as well, but sometimes, it may show abnormal ST segments and T waves. Blood pressure measurements also will usually return normal results. An examination of the heart using echocardiograph (ultrasound of the heart) imaging is required for a confirmed diagnosis of HCM. In dogs with severe HCM, the echocardiograph will reveal thickened left ventricular walls, papillary muscle enlargement, and an enlarged left atrium.