Cardiomyopathy, Hypertrophic in Cats
The heart has four chambers: two chambers at the top, the right and left atria; and two chambers on the bottom, the right and left ventricles. The left ventricle is responsible for receiving oxygenated blood from the lungs and pumping the blood out into the aortic valve, the main artery of the body, which feeds the oxygenated blood to all parts of the body. Hypertrophic cardiomyopathy (HCM) affects the left ventricle and its functional ability to pump blood into the aorta. The normal, healthy left ventricle is already thicker than the right ventricle owing to its greater workload in pumping blood out into the body. In hypertrophic cardiomyopathy, the muscle of the left ventricle is abnormally enlarged or thickened. A cat may have other diseases of the heart, but they will be independent of HCM.
There is an apparent genetic predisposition for this condition. Some families have had a high number of cases, particularly Maine coon cats, where a mutation that is associated with the disease was identified in one large family. The role of genetics has not been definitively determined in other families or breeds, although some association has been documented in American Shorthairs and Persians.
It occurs more often in cats five to seven years of age, although the age range of reported cases ranges from three months to 17 years, with most cases affecting males. Heart murmurs in older cats are generally caused by hyperthyroidism or hypertension rather than HCM.
Symptoms and Types
- Loss of appetite (anorexia)
- Weak pulse
- Difficulty breathing
- Short, rough, snapping breathing sounds (crackles)
- Abnormal heart sounds (i.e., muffled, galloping rhythm, murmurs)
- Inability to tolerate exercise or exertion
- Sudden hind-limb paralysis with cold limbs due to clot in the terminal aorta
- Bluish discoloration of foot pads and nailbeds (indicates a lack of oxygen flow to the legs)
- Sudden heart failure
The cause for hypertrophic cardiomyopathy may remain unknown in many cases. However, genetic mutations and predispositions are known to lead to HCM in cats. And though not a direct cause of the condition, hypertension and/or hyperthyroidism can further complicate HCM in cats.
You will need to provide a thorough history of your pet's health leading up to the onset of symptoms, including any information you have about your cat's genetic background.
An electrocardiogram (or EKG) recording can be used to examine the electrical currents in the heart muscles, and may reveal any abnormalities in cardiac electrical conduction (which underlies the heart’s ability to contract/beat), and can also help your veterinarian to determine the origin of the abnormal heart rhythms, if they are present. However, an ECG may not be adequate for a definitive diagnosis. Radiograph and echocardiograph (ultrasound) imaging will be more useful for visually examining the heart for enlargement or thickening of the walls, or for thickening of the mitral valve (which controls the flow of blood between the left ventricle and the left atrium). Other conditions will need to be either ruled out of confirmed before your doctor settles on HCM. There are two conditions, which are especially likely to mimic HCM, that your cat will be checked for. Your cat will need to have its blood pressure checked in order to rule out hypertension, and the blood will be tested for high levels of thyroid hormones. Hyperthyroidism will exhibit may of the same symptoms as HCM, such as lethargy, short breath, and irregular heart rhythm.