Feline Hypertrophic Cardiomyopathy (HCM) is a disease of the heart muscle which is marked by thickening of the walls of the heart. We know a lot about the effects of this condition on cats, something about its diagnosis and treatment, but very little about the cause and nothing about prevention. Studies of the incidence of HCM found it to occur in approximately 2% of cats. Male cats are at higher risk than females. No breed appears to be at higher risk. The age at diagnosis ranges from 5 months to 17 years with the mean age being about 5 years old. Research continues into the cause (or causes) of HCM. We know that there is a connection with Hyperthyroidism, especially in old cats. There may be a congenital defect involved with some of the younger patients. In most cases, the origin remains unknown.

Most cats with early HCM have no visible signs of illness. About ⅔ of cases have a heart murmur, which is usually our first hint of a problem during a routine physical exam. Some cats will have an irregular heart rhythm as well. Early diagnosis and treatment are associated with longer survival times.

Many cases of HCM are not discovered until the cat develops signs of acute heart failure. These include rapid, shallow breathing, open-mouth breathing, vomiting, weakness, fearful behavior. Blood clots may develop in the heart and travel down the aorta to block the circulation to the hind legs, causing pain and weakness or paralysis. The prognosis in these cases is guarded to poor.

Diagnosis

• Physical Exam— As noted earlier, this is often our first clue to any problem. A heart murmur, irregular heart rhythm, unusually rapid heart rate all indicate a need for investigation.

• Radiographs—Chest radiographs (x-rays) of asymptomatic cats may appear normal or may show mild enlargement of the heart. In cats with clinical signs of HCM there may be greater enlargement of the heart as well as evidence of fluid buildup in the lungs and chest cavity.

• Echocardiography—This is the most important diagnostic tool we have for HCM. This painless procedure uses sound waves to give us a 3-dimensional picture of the heart in motion. We can evaluate the thickness of the heart walls and the strength of each contraction of the heart muscle. We can also evaluate the heart valves and look for evidence of blood clot formation within the heart chambers that could lead to circulation blockage.

• Blood Tests—Although not critical to the diagnosis of HCM, a Complete Blood Count and a Chemistry Panel are important to evaluate the effect of heart disease on other essential body organs such as the liver and kidneys. They will also serve as a baseline so we can track any changes causes by the medications we will be prescribing. A thyroid profile is important for any cat over 8 years of age, since hyperthyroidism is a major factor in the development of HCM in older cats.

Treatment

The decision of whether and how to treat a cat with HCM depends on that cat’s clinical signs and the results of a complete diagnostic workup as described above.

Very early or mild cases may not require treatment, just close monitoring. More pronounced changes in the heart call for medical intervention. The following are some of the medications that may be prescribed for HCM:

• Propranolol—This beta-adrenergic receptor blocker reduces the heart rate to allow better filling of the heart chambers and improved circulation of blood to the heart muscle itself. It is given twice daily.
• Atenolol—A long-acting drug similar to propranolol, its effect on the heart is the same but the medication only needs to be given once daily. Some cats develop a loss of appetite on this drug so we don’t use it as much as propranolol.
• Diltiazem—This is a calcium channel blocker. It helps to relax the heart muscle and also improves filling of the heart and circulation. It is used less often in cats but may be useful in some cases.
• Furosemide—Better known by the brand name Lasix, this diuretic is used to draw excess fluid from the lungs. It also helps to lower blood pressure, which eases the work load on the heart muscles.

• Aspirin—Most people have learned that you can’t give aspirin to cats. Well, this is not entirely true. Cats just metabolize aspirin extremely slowly, so they need a much smaller amount and lesser frequency of dosing. In cats with HCM, low-dose aspirin therapy is used much as it is in people, to prevent formation of blood clots and thus avoid blockage of major blood vessels.

Many of these medications can be formulated to make dosing easier for you and your cat. Available forms are:

We’ll be happy to help you decide the best form of medication for you and your feline friend.