What is hypertrophic cardiomyopathy?

Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. In this disease, the heart muscle becomes abnormally thickened and stiff. This disease most commonly affects the left side of the heart, which is the side that carries blood from the lungs to the rest of the body. If the muscle gets too stiff, it can keep the chambers of the heart from filling with blood effectively. While many cats with HCM lead normal lives, cats with the disease are at risk of developing problems such as blood clots to the hind legs or congestive heart failure.

How is hypertrophic cardiomyopathy diagnosed?

The first evidence of disease is usually first noted by your primary veterinarian on a physical examination. They may notice abnormalities when listening to the heart such as a heart murmur, a gallop sound, or an abnormal heart rhythm.

A heart murmur is one of the most common reasons cats are referred for evaluation by a cardiologist; however, it should be noted that many cats with heart murmurs do not have obvious cardiac disease. Additionally, some cats with HCM do not have obvious heart murmurs. This can make diagnosis of HCM challenging, as there are not many other findings in otherwise healthy animals that can help to increase suspicion of the diagnosis prior to referral. Your primary veterinarian may perform some other testing such as X-rays of the chest or blood tests to look for the disease further.

However, the best test to diagnose HCM is an echocardiogram. This is an ultrasound of the heart. This allows for measurement of the thickness of the heart’s walls as well as assessment of the heart’s function. An electrocardiogram (ECG) may also be performed to evaluate your pet’s heart rate and rhythm. If your cat has an echocardiogram and the walls are thickened, it may also be recommended to measure your cat’s blood pressure and thyroid hormone levels. This is because high blood pressure or high levels of thyroid hormone (hyperthyroidism) may lead to an abnormally thickened heart as well.

How is hypertrophic cardiomyopathy treated?

Treatment for HCM is primarily aimed at two things: reducing the risk for blood clots as well as treating clinical signs of heart failure if present.

Specific treatments include:

• Medications to reduce the risk of blood clots such as clopidogrel. While these medications do not eliminate the risk entirely, they can help to lower it.

• Diuretic medications such as furosemide to treat heart failure. These medications will cause your pet to urinate more and drink more water. These help to eliminate excess fluid that has built up in the body.

• Physical removal of fluid from the chest or abdomen. Some cats with heart failure will develop fluid surrounding their lungs or within their abdomen. This fluid can be manually removed if needed. Typically diuretics are also used to help limit this fluid from building back up.

• Anti-arrhythmic medications to help treat abnormal heart rhythms. Some of these medications (such as atenolol) are also used to help reduce the workload of the heart if there is an obstruction to blood flow.

Other medications may also be used depending on the specific nature of the disease. If your pet is found to have something like high blood pressure or high thyroid hormone levels, treatment of those diseases may reduce the thickening and improve clinical signs if present.

A recent clinical trial in a small number of cats showed a potential benefit for a medication known as rapamycin (sirolimus). It is still too soon to tell exactly what the benefit of this medication is, though a larger trial is underway.

Should I have my cat evaluated for hypertrophic cardiomyopathy?

Cats with heart murmurs, gallop sounds, or abnormal heart rhythms would likely benefit from an echocardiogram +/- an ECG to look for evidence of heart disease. Please have your pet evaluated quickly if you see clinical signs such as:

• Rapid, labored breathing

• Open-mouth breathing

• A sudden inability to use the hind limbs

These may all be signs that indicate underlying heart disease that require immediate attention.