listen to your heart part 2: hypertrophic cardiomyopathy
If you recall from the last blog, cardiomyopathy is a primary disease of the heart muscle. In dogs, cardiomyopathy is most often due to the thinning of the heart muscles and the dilation of the chambers of the heart and is known as dilated cardiomyopathy.
Dilated cardiomyopathy used to be much more common in cats than it is today. Luckily, researchers discovered the link between taurine deficiency and dilated cardiomyopathy in cats. Taurine is an amino acid that cats cannot produce themselves. Instead, they must obtain it through their diet. In light of this discovery, commercial cat foods are now supplemented with taurine, making dilated cardiomyopathy in cats very rare.
Instead, cardiomyopathy in cats is characterized by thickened heart muscles and is called hypertrophic cardiomyopathy (HCM). Whereas a thin, dilated heart cannot contract effectively because it is like a flaccid balloon, a heart with thickened walls cannot pump blood efficiently because the chambers can’t relax enough to adequately fill with blood.
Like dilated cardiomyopathy in dogs, hypertrophic cardiomyopathy has a genetic component in cats. While certain breeds are more prone than others to the development of HCM (namely, Maine Coon cats, Persians, Ragdolls, and Oriental breeds), the average domestic shorthair cat is most commonly diagnosed.
Clinical signs are generally due to the back up of blood that occurs when the heart doesn’t pump as efficiently as it should. If you recall from the last blog on cardiomyopathy in dogs, when blood backs up, it causes fluid accumulation in and around the lungs. In turn, this can cause respiratory distress in cats. An increased respiratory rate, open mouth breathing, and panting are common in cats with HCM. Severe respiratory distress is also a concern for cats in heart failure.
Like dogs, cats with cardiomyopathy are prone to the development of cardiac arrhythmias. Cats with HCM are also more at risk to develop aortic thromboembolisms, which block the flow of blood to the hind legs. Also known as a saddle thrombus, this extremely painful condition causes sudden paralysis of the hind limbs and is often the first sign that heart disease is present. Sadly, sudden death often occurs before heart disease is detected, too.
Your veterinarian may hear a heart murmur on your cat’s yearly physical exam, or she may hear other abnormal heart sounds, like an arrhythmia or an extra heart sound known as a gallop rhythm. But often, hypertrophic cardiomyopathy goes undetected until respiratory distress or thromboembolism occurs.
There is a blood test available that we’ve discussed before that may be handy in predicting cardiomyopathy in cats. The proBNP test is used to measure the levels of a particular biomarker that increases with damage to the heart muscles. While it can be used as a screening test for feline cardiomyopathy, an echocardiogram will still be needed to confirm the presence of thickened heart muscles.
Treatment of hypertrophic cardiomyopathy centers on decreasing the symptoms caused by congestive heart failure by helping the heart pump more efficiently and by decreasing fluid buildup in the chest. Medications to decrease the chances of clot formation will also be considered.
As is the case with canine cardiomyopathy, the prognosis for cats with hypertrophic cardiomyopathy is variable, depending on the severity of the disease. Cats with mild cases can lead relatively normal lives for years with appropriate medications, but cats who are diagnosed with hypertrophic cardiomyopathy and are already showing signs of heart failure are not as lucky.
Because cats are so adept at hiding disease, even subtle changes in behavior warrant a trip to the veterinarian.