Cardiomyopathy is a big mouthful of a word, but it really just means disease of the heart muscle. This is not one single disorder but is instead, a little family of heart conditions.
Most veterinary cardiologists classify Feline Cardiomyopathy into three main types:
A fourth type, Unclassified Cardiomyopathy is intermediate in type between the others and is accepted as a separate class by most cardiologists. A so-called Arrhythmogenic Right Ventricular Cardiomyopathy has also been separately classified more recently.
Some cats go for years without any apparent signs of heart disease, others experience heart failure and death. The causes, signs, and treatments are different for each of these conditions. Each condition leads to complex changes in the heart and circulation, with overlapping changes sometimes occurring, but they are classed according to the predominant changes occurring. Rate of progression, prognosis, and other factors also vary between individual cats and between breeds.
This disorder results in the thickening of one or more parts of the heart muscle leading to changes in the way the heart pumps blood. Maine Coon cats, American Shorthair cats, Persian cats, and Ragdoll cats have increased risk of this condition. In the Maine Coon, HCM is known to be an inherited disorder, and it is strongly suspected to be inherited in the other breeds.
Typically, the age of onset is young adulthood, with males more frequently affected than female cats. Note that cats may be very young (especially in Ragdoll cats) or quite well along in adulthood (10 years of age) when the condition is first diagnosed. Murmurs or gallop rhythms may occur, or no clinical signs may be noted.
Heart failure may occur quickly once the heart becomes affected, and fluid buildup in the chest cavity can make breathing very difficult. These cats may also get blood clots in the arteries, especially in the arteries that supply the hind limbs.
HCM is the most common of the cardiomyopathy classes, and is the most likely to be picked up during an annual checkup of an apparently healthy feline patient. General signs of malaise such as poor appetite, weakness, and perhaps vomiting may be noted, but it is not unusual for the cat to be quite normal at home until the heart goes into advanced failure.
This condition leads to a thinning of the muscle wall of the heart, resulting in chamber dilation. These flabby walls do not pump very efficiently. Once a common condition, modern diet formulations with higher levels of an essential amino acid taurine have led to a significant drop in disease rates. Usually the diagnosis is made in slightly older cats that are showing signs of heart failure. A slow heart rate, low blood pressure, and low body temperature may be noted, and these cats may also get blood clots in the arteries. There may be gallop rhythms or murmurs noted when the vet checks the heart with the stethoscope. These days, this condition is seen most commonly in cats fed dog food, or fed homemade diets without taurine supplementation.
In this case, the heart becomes constricted in pumping ability due to loss of elasticity throughout the heart muscles which makes the heart function in a “stiff” fashion. Scar tissue, or in other cases, inflammation of the muscles may be responsible for these changes. Rhythm disturbances and murmurs may be heard. Blood clots may get lodged in the arteries.
Blood Clots of the Arteries
Artery blood clots, termed systemic thromboembolism can lead to paralysis of the hind limbs with associated dark, cold toe pads. Depending on which part of the body the clots end up, other signs may be noted but most frequently, it is rear limb problems that are noted. Cats with an artery clot are very painful, and if the clot completely blocks the main blood supply to the rear limbs, she cannot move. This may lead some caregivers to think their cat may have been hit by a car or perhaps has taken a fall. A professional assessment will rule out other causes of hind end problems.
Treatment of the condition will be tailored to the needs of each individual cat, but supporting the strength of heart contractions, reducing fluid buildup, nursing and supportive care (including nutrition), and dietary adjustments are some of the common strategies a veterinarian will apply. If the cat also has blood clots, other therapy will be added to address that specific problem. Pain therapy and medicines that have an effect on clotting will be used to help manage this latter complication.