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Hypertrophic Cardiomyopathy Genetic Mutation in Cats

Hypertrophic cardiomyopathy is the most common form of heart disease in the cat. In many breeds it is an inherited disease. Our laboratory has identified two mutations responsible for the gene in some cats. One genetic mutation is found predominantly in Maine Coon cats and the second genetic mutation is found predominantly in Ragdoll cats.

It should be noted that in human beings with the same disease, there are many different genetic mutations which can cause this disease. It is likely the same in the cat but additional mutations have not yet been defined.

Very importantly, the absence of the mutation in a cat DOES NOT mean that it will never develop the disease. It means that it does not have the only known mutation that can cause the disease in the cat at this time. In the future, additional mutations may be identified that may be tested for as well.

Dilated Cardiomyopathy (DCM)

DCM is a disease of the heart muscle that results in weakened contractions and poor pumping ability. As the disease progresses the heart chambers become enlarged, one or more valves may leak, and signs of congestive heart failure develop. The cause of DCM is unclear in most cases, but certain breeds appear to have an inherited predisposition. Large breeds of dogs are most often affected, although DCM also occurs in some smaller breeds such as cocker spaniels. Occasionally, DCM-like heart muscle dysfunction develops secondary to an identifiable cause such as a toxin or an infection. In contrast to people, heart muscle dysfunction in dogs and cats is almost never the result of chronic coronary artery disease (”heart attacks”).
Dogs with heart failure caused by DCM often show signs of left-sided congestive failure. These include reduced exercise ability and tiring quickly, increased breathing rate or effort for the level of their activity excess panting, and cough (especially with activity). Sometimes the cough seems soft, like the dog is clearing its throat. Poor heart pumping ability and arrhythmias can cause episodes of sudden weakness, fainting, or sudden death as noted above. Some dogs with DCM experience abdominal enlargement or heavy breathing because of fluid accumulation in the abdomen or chest, respectively. Presence of any of these signs should prompt a visit to your veterinarian to determine if heart failure (or another disease) has developed.

More advanced signs of heart failure could include labored breathing, reluctance to lie down, inability to rest comfortably, worsened cough, reduced activity, loss of appetite, and collapse. A veterinarian should be consulted right away if these signs occur. Signs of severe heart failure may seem to develop quickly with DCM, but the development of underlying heart muscle abnormalities and progression to overt heart failure probably takes months to years.

A cardiac exam by a veterinarian can detect abnormal heart sounds (when present) and many signs of heart failure. Usually chest radiographs (x-rays), an electrocardiogram (ECG), and echocardiogram are performed to confirm a suspected diagnosis and to assess severity. Echocardiography also can be used to screen for early DCM in breeds with a higher incidence of the disease. Resting and 24-hour (Holter) ECGs are sometimes used as screening tests for the frequent arrhythmias that usually accompany DCM in some breeds, especially boxers and Doberman pinchers.

What can be done if my pet has this disease?

Asymptomatic (subclinical) cases of DCM may be treated with enalapril® or another ACE inhibitor to slow progression of the changes leading to heart failure. Other medications and strategies are also used as signs of heart failure develop and/or if rhythm abnormalities are present. Therapy is always tailored to the needs of the individual patient. Since this disease is not reversible and heart failure tends to be progressive, the intensity of therapy (for example, the number of medicines and the dosages used) usually must be increase over time.

Recently a Boxer dog with a heart rhythm disturbance due to cardiomyopathy had a defibrillator surgically placed to control his heart rate.

This Pet Health Topic was written by O. L. Nelson, DVM, MS, Diplomate ACVIM (Cardiology & Internal Medicine) Washington State University.