Hypertrophic Cardiomyopathy HCM


Definitive answers – excerpts from Dr. Mark Kittleson’s article for Bengals Illustrated.  
Dr. Kittleson is considered the foremost authority on the topic of HCM in cats.

Mark D. Kittleson, DVM, PhD
Credentials: DVM, PhD Diplomate ACVIM (Cardiology); Professor, Department of Medicine and Epidemiology, UC Davis. Dr. Kittleson maintains a colony of Maine Coon and Maine Coon cross cats with feline familial HCM for the past twenty years. He has documented the heritable nature of HCM in this colony and is the co discoverer of the first mutation to cause HCM in cats.

Dr. Kittleson, a veterinary cardiologist at the University of California, Davis provided Bengals Illustrated with the prestigious honor of answering several questions regarding feline hypertrophic cardiomyopathy, HCM. Dr. Kittleson is well known in the scientific community and is a leading authority in veterinary cardiology.

Cross-sectional view of a left ventricle from a cat with severe HCM—the photograph shows it is severely thickened.

HCM is thickening of the wall of the left ventricle. Severe thickening results in scar tissue formation. The thickening and scar tissue make it difficult for the left ventricle to relax. If severe, this can result in heart failure, the accumulation of fluid in or around the lungs. This fluid accumulation, when severe, results in rapid and difficult breathing. The left atrium (*the chamber behind the left ventricle) enlarges also in cats whose left ventricle cannot relax properly. This enlargement causes blood flow through this chamber to slow and so blood to sludge, predisposing to clot formation. When a clot breaks loose from its attachment in the left atrium, it travels down the aorta to the rear legs, blocking blood flow and causing the sudden onset of paralysis and severe pain (so-called saddle thromboembolus). The scar tissue can also predispose to abnormal electrical activity in the left ventricle which is manifested as an arrhythmia. The arrhythmia that is seen is thought to predispose cats with HCM to sudden death. So cats with severe HCM can develop heart failure, die suddenly or experience the pain of a saddle thromboembolus. All of these are devastating problems.

HCM affects all mammals. It has been documented in the Bengal cat, Maine Coons, Ragdolls, Sphynx, and other pedigreed breeds … as well as cats of a non-pedigreed heritage. Reputable breeders within the Bengal community regularly have their cats screened by a board certified cardiologist to try to detect any abnormalities early on.  This responsible and consistent screening makes the breed healthier as breeders seek to eliminate cats that screen positive for HCM.

The following are excerpts from the five pages of questions and answers with Dr. Kittleson:

Bengals Illustrated: How is HCM acquired?

Dr. Kittleson: There are very few causes of HCM in any species, including cats and humans. The vast majority of the causes are mutations in genes that encode for what are called sarcomeric proteins. Sarcomeres are the microscopic units in heart muscle that actually contract. Mutations cause abnormal proteins to be formed that alter the function of these sarcomeres that force the heart to build new ones to compensate. This produces the thickening that we see grossly. There are other less common genetic causes and rare metabolic causes such as excess growth hormone and excess parathyroid hormone that are usually associated with hormone secreting tumors.

Bengals Illustrated: Can it be determined if a cat has HCM without cardiac screening?

Dr. Kittleson: No. Many cats with HCM will have a heart murmur, but not all do, and there are several other common causes of a heart murmur in cats.

Bengals Illustrated: Are there subtle signs that a pet owner or breeder might notice indicating a possible HCM diagnosis?

Dr. Kittleson: Not usually. Cats are extremely good at hiding problems and there is no evidence that an owner can see until the disease is so severe that heart failure is present. Heart failure results in accumulation of fluid either in or around the lungs. The first sign of this is an increase in breathing rate, which almost no one picks up on.  Most owners don’t notice a problem until labored breathing is present, often not until it’s so severe that an emergency situation exists.

Bengals Illustrated: How common is genetic HCM in cats?

Dr. Kittleson: We don’t know about exact mutational causes since we’ve only found two mutations so far. In humans there are currently 434 mutations. However, at this time it is assumed that all feline HCM is genetic, especially when it occurs in specific breeds.

Bengals Illustrated: Is there a difference between cats that screen positive for HCM at a young age versus those who do at an older age?

Dr. Kittleson: Sex is one factor. Males get the disease younger and often get a more severe form of the disease. Consequently, HCM is often thought to be more predominant in males when, in fact, males and females have an equal incidence of the disease.

Bengals Illustrated: Are their any statistics for the incidence of HCM in Bengals as a breed?

Dr. Kittleson: There really aren’t any statistics for any breed except possibly Maine Coons, but data there is at least somewhat contradictory.  Samples sent into Dr. Meurs lab at Washington State suggest that 30% of the Maine Coon cat population has the one mutation identified in that breed so far. That, however, is a biased sample of samples submitted by breeders. A much smaller study suggests that the incidence may be much lower.

Bengals Illustrated: Once a cat is diagnosed with the disease, how long does the cat have to live?

Dr. Kittleson: That is highly variable. It is extremely dependent on the severity of the disease. A cat that has mild to moderate HCM that does not progress can live a normal life. A cat with severe disease that is in heart failure usually has months to live. However, a cat with severe HCM that is not in heart failure can be in trouble very soon after diagnosis or can live for years without difficulty, making it impossible to predict how they will do. For example, I have a Maine Coon cat in my colony that I thought would get into trouble and die four or five years ago that is doing great.

Bengals Illustrated: What does equivocal mean? Should an equivocal cat be bred and why would an ‘equivocal” cat later test normal?

Dr. Kittleson: Equivocal means uncertain and is a fancy way of saying “I don’t know.”  So the examiner does not know if the cat is normal or has HCM. Period. Nothing more should be read into this. On a future exam the cat may be called normal, equivocal or positive by the same examiner. And if another examiner looks at the same cat he or she may come up with any of the same three choices. Certainly there are some cats that have subtle evidence of HCM that fall into this category that then go on to develop clear evidence of HCM over time, but this is definitely not always the case. Obviously, having a cat that falls into this category makes breeding decisions very difficult.

Bengals Illustrated: How often should breeding cats be screened for HCM?

Dr. Kittleson: Yearly during the first 3-4 years of life and less often after that.

Take a tour through a normal functioning feline heart:

KPN interactive: Graphics, animation & additional programming: Matthias Kaestner


For the complete interview see Bengals Illustrated back issue Origins and inspirations.
Click on the Bengals Illustrated back issue to the left.

Other questions and answers not included in this condensed-for-web version included:

Regarding enlarged papillary muscles, Herbal treatments for HCM, Screening schedules, Diet and HCM, and Much More!




3 responses to “Hypertrophic Cardiomyopathy HCM”

  1. Tyler says:

    I lost my 22 mo old male bengal cat to this issue three days ago. He was seemingly fine until one day he was extremely lethargic and breathing very heavily. Within hours he was basically gasping for air. We took him to the vet, who put him in an oxygen cage, and provided us with X-Ray imagery of his lungs filled with liquid, and told us it was HCM.

    Sadly, we couldn’t afford the medical care he required in order to try to prolong his life by a few months, and he had to be put to sleep to stop his suffering.

    This article really explained what happened to him. One thing that worries me is that his bengal brother (same father different mothers) also has a heart murmur.

  2. D.R. Mac Fadyen says:

    Are beta blockers ever used for HCM in cats?

    • Bengals Illustrated says:

      Beta blockers have been used for HCM felines. For more information – check out the latest issue of Bengals Illustrated on the back issues page (The Hot Topics Issue).