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.
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 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.
Treatment for HCM is normally only advised if the dog is experiencing congestive heart failure, severe arrhythmias (abnormal hearth rhythm), or frequent loss of consciousness. If the dog has left-sided congestive heart failure, diuretics and ACE inhibitors will usually be administered. In dogs with arrhythmias, beta adrenergic blockers or calcium channel blockers are used to improve oxygenation of the heart and to bring down the heart rate. Dogs that are not experiencing congestive heart failure due to HCM can usually be treated on an outpatient basis, where exercise restriction and a low sodium diet will be part of the treatment.
Living and Management
Follow-up treatment for HCM will depend largely on how severe the symptoms are. Repeated radiograph and echocardiograph imaging will be needed to follow the progress of the therapy, to watch for advancement of the disease, and to check on whether adjustments to medication are necessary. Because HCM is so rare in dogs, little data is available on the prognosis. If your dog does have congestive heart failure caused by HCM, the prognosis will usually be poor. Survival will depend largely on the extent of the disease. Your veterinarian will be able counsel you on your dog's chances for survival, and on quality of life practices you can put into place for your dog.