Cardiac Disease in Cats
It is always heartbreaking, to lose a beloved pet. But to lose one suddenly, with no signs of illness that you would gladly have treated, is perhaps the cruellest way to be deprived of a loving companion. Many people find themselves doubting their care of the animal in question. Being only human, we often blame ourselves. One of the major causes of sudden death in felines, are cardiac disorders.
Despite some popular beliefs, these are not the "invention" of purebred animals. Just as many household pets can be affected as the cat with a pedigree. Heart disease makes no distinction. It is perhaps recorded more in purebreds, because the possibility of a genetic cause versus a hereditary one can have great impact on a breeding program, and so more tests and post mortems are done.
In general, heart disorders are discovered by veterinary examination, which may detect a murmur or arrhythmia, confirmed on further testing by electrocardiogram and/or ultrasound. However, many cases of moderate to severe heart disease go undetected until a sudden collapse or death. Cats who fall over or become victim of sudden hind end paralysis, may have had a stroke due to a saddle thrombus: a blood clot thrown from the heart chamber, due to heart disease.
One of the disorders that has been the subject of widespread research is hypertrophic cardiomyopathy. This is a thickening of the left, and sometimes right heart walls, and septum, due to the overproduction of heart proteins or sarcomeres. It results in poor relaxing and filling ability, so that when less blood enters the heart, less is put back into the body. It may not show itself at all until a cat dies suddenly, and on post mortem is found to have a disarray of the myocardial fibres, excessive sarcomeres, and a grossly thickened left ventricle and septum, effectively keeping the heart from functioning.
Cardiomyopathy is recognized in three forms: dilatative, restricted, and hypertrophic. Restricted may be show itself as a result of distortion of the papillary muscle or chordae tendae due to inflammatory cell infiltration. Dilatative, characterized by the enlargement of the ventricle and thinning of its wall, results in a loss of cardiac contractility, and was diagnosed as a dietary deficiency, generally of taurine. It is rarely seen now. The most prevalent form is hypertrophic cardiomyopathy, affecting males more often than females, and frequently cats under the age of two, or over the age of six years.
A cat suffering from HCM or one of the many other cardiac disorders of felines, may or may not: pant, be lethargic, vomit, have fluid in the abdomen, raspy breathing, loss of appetite and sudden collapse. The good news is that diagnosed in time, HCM is a treatable disease, using drugs which relax the thickened heart walls, allowing for more flexibility and flow of blood in and out.
There are however, a number of diseases that mimic HCM, and are often misdiagnosed, particularly without a full post mortem (including histology using all the major blood filtering organs). These include: -endomyocarditis -aortic stenosis -excessive catecholamines -acromegaly -Tetralogy of Fallot -dystrophin deficiency in cats with muscular dystrophy
In assessing a cat for cardiac disease, a basic exam is necessary, followed by any or all of the following: chest x-ray, electrocardiogram, cardiac ultrasound, blood and other tests. Certainly blood and urine testing will tell a lot about possible kidney or thyroid conditions, and rule out some of the imitative disorders that can lead to misdiagnosis.
For a breeder, the presence of HCM can be a nightmare. Because the feline genome has not been mapped yet, it is impossible to tell if the disease is hereditary in all cats. To date, the only studies with any reasonably accurate results, were done by Dr. Mark Kittleson of UC-Davis, on Maine Coon and American Shorthair cats. In those, he was able to prove that affected to affected breedings, always produced affected offspring, as did affected to unaffected cats. Because there were limited numbers of unaffected cats available, his matings of unaffected to unaffected, were not sufficient to make any firm declaration that the cats in question could not carry the gene and pass it on, without expressing it.
In humans, it has been proven by genetic mapping, that not only is HCM autosomal dominant (meaning only one parent has to have it, or carry it), but that it can be carried by one parent, who is never affected by the disease themselves. Unfortunately, this kind of information is not yet available in felines. And just as some disorders are ethnic in origin for humans, so may some cat disorders be breed specific, or shared by breeds with common ancestors.
For pet owners who truly need to know why a cat has died, particularly in cases of sudden and unexplained deaths, a post mortem is the only sure way to find out, although with HCM and other cardiac disorders, you may not get a definitive answer. For breeders, it is almost mandatory that you get not only a thorough post mortem, but testing of siblings and parents. If there are any signs of cardiac disease in any form, it is then up the breeder to make the decision to continue with those bloodlines or not.
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