Ask the Edmonds Vet: What’s cardiomyopathy?

By Dr. David Gross

My mother’s Maine Coon cat has cardiomyopathy. What is that?

“Cardio” obviously pertains to the heart, “myo” pertains to muscle and “pathy” signifies pathology or abnormality. Therefore, cardiomyopathy is pathology or abnormality of the heart muscle. We describe two kinds of cardiomyopathy; hypertrophic and dilated. Both types occur because of genetic mutations in one or more of the various proteins that comprise the heart muscle.

A study published in 1993 in the American Journal of Cardiology compared lesions found in 38 humans, 51 cats and 10 dogs that died of spontaneous hypertrophic cardiomyopathy. The authors of the paper discovered almost identical changes in all of the subjects.

Hypertrophic cardiomyopathy results in an increase in the volume of the heart muscle. As the muscle, usually that of the left ventricle, the chamber of the heart responsible for pumping blood out into the body, is forced to work harder it becomes thicker. As this happens the muscle also becomes stiffer, less compliant, and the result is that the ventricle is less able to relax and fill with blood during the resting phase between beats, called diastole. Eventually the left ventricle cannot fill enough to pump enough blood to meet the metabolic demands of the body and the resulting condition is “heart failure.”

These same changes can also occur in the right ventricle, the heart chamber responsible for pumping blood to the lungs. Sometimes both chambers are afflicted. The results are left heart failure, right heart failure or total heart failure. Hypertrophic cardiomyopathy seems to be particularly prevalent in Maine Coon, Maine Coon crossbreds and Ragdoll cats.

The other type of cardiomyopathy, dilated, is the yang of hypertrophic’s yin. The myocardium dilates and becomes thinner rather than thicker. This condition is also most often a genetic defect and thought to be an autoimmune disease as are Lou Gehrig’s disease, Cohn’s disease, lupus and many others. The myocardium stretches and becomes weaker over time. Eventually the affected heart chamber(s) stretch to the point where the beating muscle loses strength. When it contracts, it can no longer expel enough blood and heart failure occurs. Again, either the left, right or both ventricles can be affected.

Large breeds of dogs, especially Irish Wolfhounds and Doberman Pinschers, seem to be the most afflicted by this condition but it has been found in German Shepherds, Boxers, and English Cocker Spaniels, mixed breeds and occasionally other breeds. For unknown reasons dilated cardiomyopathy kills males two to three times more commonly than it does females.

Genetic lesions resulting in myocardial changes closely resembling cardiomyopathy have been reported in Polled Hereford cattle, mustached tamarinds (monkeys) and pygmy sperm whales. Cardiomyopathies can also develop as the result of persistent rapid heart rate, high blood pressure, either systemic or pulmonary, diseases of the outflow valves of either the right or left ventricles (aortic or pulmonary valves), following treatment with certain chemotherapeutic agents, following obstruction of the coronary arteries, and after exposure to a host of toxic substances.

If your pet shows signs of lethargy, labored breathing, decreased levels of activity and tiring easily, take it to your veterinarian for a checkup. The earlier a heart condition is caught, the more successful the treatment and/or management is.

D. R. Gross graduated from Colorado State University’s veterinary school in 1960 and was in private practice for ten years. He enrolled in graduate school at Ohio State University earning a M.Sc. degree in 1972 and a Ph.D. degree in 1974. He retired in 2006 as Professor and Head of Veterinary Biosciences, at the University of Illinois, Urbana-Champaign. Dr. Gross is a Fellow of the Cardiovascular Section of the American Physiological Society. During his academic career, he published over 90 papers in refereed scientific journals and over 100 abstracts in proceedings of scientific meetings.

Dr. Gross is the author of “Animals Don’t Blush,” which describes the unique patients and even more unique clients of a veterinary practice in Sidney, Montana in the early 1960s.

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