Hypertrophic cardiomyopathy is a type of heart disease in which the heart muscle tissue becomes unnecessarily and excessively thickened. This thickening usually occurs in the left ventricle of the heart, limiting the amount of space available for blood as well and restricting the ability of the heart to move properly. The heart is unable to fill and pump effectively. Inability of the left ventricle to relax and stretch effectively may lead to a build-up of blood upstream, ultimately forcing fluid from the pulmonary capillaries into the lungs and chest cavity. This is known as pulmonary edema and pulmonary effusion, commonly called “congestive heart failure”. The disease can range from mild to severe.
HCM is the leading cause of spontaneous death (caused by arrhythmias or aortic thromboembolisms) in indoor adult cats because most cats with HCM show very few symptoms. Mildly increased respiratory rate, or decreased appetite are sometimes noted. Examination will occasionally yield an increased heart rate, heart murmur, or gallop rhythm in more advanced disease states.
About 15% of all domestic shorthairs (regular house cats) suffer from HCM. This number increases to 33% for Maine Coons and Ragdolls, and lies between 15%-33% for other purebreds, such as the Siamese, Persian, Himalayan, Burmese, Abyssinian, Bengal, etc. HCM is thought to be an inherited condition, and is usually diagnosed in adult cats, but can be diagnosed at any age. No viral or nutritional causes of HCM have ever been identified.
Since most cats are very good at hiding disease, and many do not show symptoms, HCM is usually diagnosed upon necropsy (after death) or by laboratory testing to look specifically for this condition. Some of these diagnostic tests include:
Radiographs: Radiographs of the chest can show fluid retention in the lungs or chest cavity, as well as occasional slight enlargement or distortion of the shape of the heart. Mild disease may not be detected on radiographs, which can not be used alone to diagnose HCM.
Pro-BNP Blood Test: This test is drawn in the clinic and results are returned within a few days. Pro-BNP tests detect levels of N-terminal pro-B-type natriuretic peptide in the circulating blood. Since this peptide is produced in the face of heart disease, increased levels indicate probable heart disease and an echocardiogram is recommended.
Echocardiogram): An ultrasound of the heart is the most effective tool for diagnosing HCM, allowing visualization of the structure and function of the heart muscle. Echocardiograms can be done here at River Road Veterinary Clinic, by Dr. Kelloway, a traveling veterinarian. They can also be done by Dr. Don Brown, a board-certified cardiologist at PEAK in Williston, VT.
Complete Blood Work: A Complete blood count, Chemistry panel, and Thyroid monitoring panel may indicate problems with other organs that can mimic or cause heart disease.
Genetic Blood Test: This blood test will only identify one specific genetic mutation that causes HCM in Maine Coons and Ragdolls.
If your cat is diagnosed with HCM it is important to monitor them closely and begin medical treatment. Treatment is usually a combination of medications and diet change. These treatments can include:
Atenolol: If your cat is asymptomatic, he will be placed on a medication called atenolol, which lowers blood pressure thereby decreasing stress on the heart. Blood pressure should be monitored at least every 6 months while on this medication.
Aspirin: Asymptomatic cats are also placed on 1 baby aspirin every 3 days. This helps to thin the blood, reducing the risk of clot formation.
Benazepril: Once your cat begins showing symptoms of HCM, additional medications will likely be added. Benazepril is an ACE inhibitor that treats high blood pressure.
Furosemide: If your cat is showing symptoms of Congestive Heart Failure (CHF) a diuretic is often necessary to remove excess fluid from the chest and lungs. Furosemide is the most commonly used diuretic in cats. It is important to note that the use of diuretics can exacerbate already present kidney disease.
Pimobenden: Previously used only in dogs, Pimobenden is a vasodilator and calcium sensitizer that effectively decreases the workload of the heart.
Diet: A cardiac approved diet low in sodium is recommended for all cats with a heart condition. Hills Science Diet k/d or Purina NF are excellent choices.
Restricted Activity: Restricting activity will decrease stress placed on the heart.
Most cats have a fair to good prognosis with early diagnosis. The severity of the disease at the time of diagnosis is directly related to your pet’s prognosis. With proper treatment and care the life of your cat can be extended by more than 5 years.