Cats can develop a number of diverse heart diseases. The most common of these are diseases that involve hypertrophy, or enlargement, of the heart muscle, which is the myocardium. The general term for this in veterinary medicine is cardiomyopathy. Cats can develop hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM) and much less frequently dilated cardiomyopathy (DCM). Cats also can suffer from something called arrhythmogenic right ventricular cardiomyopathy, myocarditis and arterial thromboembolism. Some feline heart disease cannot easily be classified. These conditions may be genetic, caused by an anatomic or physical abnormality or be caused by an underlying primary medical condition. Sometimes, the cause is never determined.
Types of Heart Disease in Cats
Hypertrophic Cardiomyopathy (HCM)
Hypertrophic cardiomyopathy occurs when areas of the heart muscle become thickened and noncompliant, which eventually adversely affects the heart’s ability to pump blood properly. HCM is the most common heart disease of domestic cats. There is thought to be a genetic basis to HCM in cats. Certain breeds are predisposed, including the Maine Coon, Persian, Ragdoll and American Shorthair; littermates and close relatives of affected cats are also at an increased risk of developing the disease. Many cats develop HCM as a secondary response to some other stress or disease. For example, cats over 6 years of age are predisposed to hyperthyroidism, which puts abnormal demands on heart function and commonly contributes to cardiac complications. Clinical HCM tends to be more common in middle-aged to older male cats but can occur in either gender and at any age.
Restrictive Cardiomyopathy (RCM)
Restrictive cardiomyopathy occurs when the elasticity of the heart muscle is reduced through a process called “fibrosis”, which eventually thickens, scars and deforms the heart muscle and chamber walls. The cause of RCM is not well understood but probably is due to a number of things acting together. RCM is usually a disease of middle-aged to older cats.
Dilated Cardiomyopathy (DCM)
Dilated cardiomyopathy involves poor heart contractility with an accompanying thinning of the walls around all heart chambers. In time, the chambers become enlarged/dilated, and the heart is unable circulate the body’s required volume of oxygenated blood. While DCM used to be common in companion cats of all ages, with no breed or gender predisposition, it is rarely seen today. In the late 1980s, it was discovered that most commercial cat foods were deficient in taurine, a nutrient essential to the health of cats. This dietary taurine deficiency was closely related with feline DCM. Once the dietary corrections were made, DCM decreased dramatically in domestic cats.
Arrhythmogenic Right Ventricular Cardiomyopathy
Cats can also develop cardiomyopathy that primarily affects the right ventricle, with chamber enlargement and wall thinning similar to that seen more diffusely with DCM.
Mycarditis is inflammation of the heart muscle and adjacent structures. A viral cause has been suggested but not conclusively established. Bacterial causes are reported as well. Acute sudden death is the most common clinical presentation of myocarditis in cats.
Cats are especially prone to arterial thrombosis and embolization that can accompany any of the forms of feline cardiomyopathy. The association is due to diminished or interrupted blood flow through the arteries and veins, possible clotting abnormalities and accompanying clot formation. The signs normally come on very suddenly and are dramatic, involving slight or incomplete paralysis of one or more limbs (paresis), decreased ability to ambulate, pain, vocalization and visible distress, low body temperature, loss of sensation, organ failure and sometimes death, among others. These thromboembolisms tend to lodge in particular parts of the cat’s circulatory system.