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HCM is the # 1 Killer of Indoor Adult Cats of Any Breed

HCM is the # 1 Killer of Indoor Adult Cats. Although some veterinary and pet health articles provide  lists of cat breeds with HCM (hypertrophic cardiomyopathy), even going so far as to state these breed are the only cat affected by HCM, in reality HCM occurs in every single cat breed, including non-pedigreed household pets.  In fact, HCM  is the #1 killer of any indoor adult cat (an outdoor cat is more likely to  die a violent death or from an infection). 

Fortunately, HCM in Siberian cats who are not inbred is relatively rare.  

Why is inbreeding so dangerous?  Inbreeding collects together similar traits. This is beneficial in terms of getting cats to resemble each other ("set type"), but is a negative practice in terms of maintaining the genetic diversity necessary in a healthy breed.  When genetic diversity is decreased, the chances of a cat "collecting" a set of disease producing genes is increased.

HCM is a genetic disease that is dominant with incomplete expression. Inbreeding is especially dangerous for a disease like HCM, a disease that is genetic in cause, is dominant (if the cat inherits the gene it has the disease), but is incomplete in expression (the severity and time of expression of the disease varies widely).  This leads us to believe that there are co-inherited genes that either mitigate or exaggerate the effects of the HCM gene.

Restricting one's breeding program to maintain consistency in looks reduces genetic vitality. By selecting for certain visual traits for the show wins, and ignoring the need to include genetic diversity in one’s lines, the resultant reduction in genetic variation makes it more likely that any diseases inherited will be expressed, often severely . This is not an issue restricted to one country, or any one breed. Instead, it is related to teh cumulative effects of each individual breeder's practice in selecting healthy, genetically unrelated diverse cats for breeding.

It's more expensive and difficult to breed ethically. Breeders who make this  ethical - but more difficult, expensive, and time consuming - choice to select and breed from unrelated or lightly related cats combined  with a health testing program designed to remove affected cats from breeding,  will produce healthier and better tempered cats. Cats much less likely to have inherited and to die from HCM.

Hypertrophic Cardiomyopathy in Cats

What is Hypertrophic Cardiomyopathy (HCM)?

It is the most common cause of heart disease in cats, and the most frequent cause of spontaneous death in indoor adult cats.  In cats with this condition, the walls of the ventricles become thick. However, because the muscle fibers are replaced by fibrous connective tissue (scar tissue), the thicker heart walls do not translate into increased pumping power. In fact, the heart is actually weakened as the affected wall of the heart becomes less elastic and the heart chambers get smaller.

What Are the Signs of HCM?

Congestive heart failure occurs frequently in cats with hypertrophic cardiomyopathy. Typically, the left side of the heart is more involved than the right, so the signs of hypertrophic cardiomyopathy are those of left-sided congestive heart failure. Signs of left-sided congestive heart failure are:

  • difficulty breathing,
  • an increased respiratory rate,
  • an increased respiratory effort,
  • increased heart rate,
  • weakness,
  • lethargy,
  • lack of appetite,
  • fainting spells (usually caused by an irregular heart rate known as an arrhythmia), and
  • cyanosis (a purple or blue color in the gums due to a lack of oxygen) in extreme cases.
  • Cats with hypertrophic cardiomyopathy may also develop an aortic thromboembolism. This occurs when a blood clot breaks loose from the heart and becomes lodged at the end of the aorta causing the blood flow to the hind legs to stop. Cats suffering from aortic thromboembolism will suddenly become paralyzed on their hind legs or have a difficult time walking and will be quite painful.
  • In some cases, young apparently healthy cats may develop signs of hypertrophic cardiomyopathy while undergoing a routine surgical procedure, such as a spay or neuter. Signs may also appear shortly after the procedure is finished. It is likely in these cases that the heart condition existed prior to the procedure but was asymptomatic (not causing signs of illness) and so not diagnosed.
  • Sometimes the first sign of HCM is sudden death
How is HCM Diagnosed?
The be diagnosis is made by combining clinical findings with results of echocardiography. Cats with the clinical findings of aortic thromboembolism or acute pulmonary edema with gallop rhythm or systolic murmur, valentine-shaped heart with prominent left auricle and pointed left apex, vigorous left apical impulse, and left axis deviation of the ECG are very likely to have idiopathic HCM.
How is HCM Treated?
Treatment will depend on the progression of the disease in the cat, and includes:
  • Beta Blockers: atenolol and metoprolol
    These drugs help improve the "filling" function of the left ventricle, which will subsequently increase the volume of blood flowing to the lungs, helping to decrease pulmonary edema.
  • Calcium Channel Blockers : diltiazem
    Also help improve heart function, by reducing heart rate and myocardial oxygen consumption.
  • Treat underlying conditions
    Most often Hyperthyroidism and/or hypertension (high blood pressure.)
  • ACE Inhibitors:enalapril or benazepril
    Ongoing clinical trials with cats seem to indicate that these drugs may work better than Beta Blockers, for improving heart function.
  • Diuretics: Help to reduce pulmonary edema. Because of the potential for negative side effects. renal function must be monitored carefully when diuretics are used.