Heart disease is a common cause of illness in domestic cats. It is frequently called a “silent killer.” This is especially true in feline medicine due to the lack of early signs of disease and the tendency for cats to hide illness. While other species may exhibit early signs, such as coughing or exercise intolerance, cats are often subclinical (without signs) until the disease has become advanced.
Heart disease refers to any dysfunction of the heart and is different from heart failure. Many types of heart disease exist in cats, but the most common are called “cardiomyopathies” (diseases of the heart muscle). Other types of heart disease may include valve disease (such as mitral insuf- ficiency), birth defects (such as holes or strictures) or other conditions.
The most common heart disease in cats is hypertrophic cardiomyopathy (HCM). This disease is characterized by a gradual thickening and weakening of the heart muscle. As the muscle thickens, there is less room for blood to fill the heart and the muscle is less able to pump blood effectively as it weakens. There are two primary forms of HCM — a genetically linked form that is often early onset and occurs in some breeds (Maine Coons, Ragdolls, Rexes, Sphynxes and others) and a sporadic form that may occur in any cat at any age.
Dilated cardiomyopathy (DCM) used to be a common disease in cats and is characterized by a thin and “flabby” heart muscle. DCM was almost exclusively caused by a deficiency of a nutrient called taurine in the diet. In recent decades all commercial foods have been supplemented with taurine, rendering the disease less common. DCM may still occur for other reasons, or in cats fed homemade or poorly formulated diets defi- cient in taurine. It is important to note that taurine supplementation is likely not helpful in cats with other forms of heart disease.
Other cardiomyopathies exist, such as restrictive or unclassified cardiomyopathy; however, they are less common.
Early signs of heart disease in cats are easy to miss as they are either non-existent, or so subtle and non-specific that they are rarely noticed by owners. To further complicate matters, cats seem to know their own capabilities and limitations and tend to restrict their level of activity, which can further mask clinical signs.
Heart murmurs may be present in cats with heart disease. A murmur is an extra “whooshing” noise between normal heart sounds due to turbulent or abnormal blood flow. Some kittens may have a transient “physiologic” murmur that is of no signifi- cance that disappears as they mature. Approximately half of adult cats with heart murmurs will develop heart disease, while the other half will be healthy. The murmur’s loudness is not always associated with disease severity. While cats with heart murmurs should be monitored due to higher risk of disease, they will not all experience heart failure. Only about half of cats with heart failure will have a murmur.
Cats may also have an arrhythmia (irregular heart rhythm that may be fast or slow) or a gallop (an extra heart sound). Unlike a murmur, these are almost always signifi- cant in cats and should be investigated.
Other signs of heart disease are less specific and may include weight loss, loss of appetite, lethargy or collapse. Swollen abdomen and coughing are very uncommon in cats, unlike humans and dogs.
Cats with heart failure may develop slow and progressive signs, or may present acutely ill. Two main acute syndromes occur in cats — congestive heart failure (CHF) or feline aortic thromboembolism (FATE).
Cats with CHF develop an increased respiratory rate (generally more than 60 breaths per minute). They often breathe with an open mouth, may struggle for breath and have blue-tinged gums. Fluid may be present within the lungs (pulmonary edema) or around them (pleural effusion). Fluid may also build up in the abdomen or within the heart sac, though these signs are seen less commonly.
Cats with FATE generally lose the function of one or more limbs. Initially, the embolism is very painful, with loss of pain sensation occurring over the next few hours. The affected limbs are cold to the touch and without pulses in the arteries to the affected leg(s), and the limbs are weak or paralyzed. This is a very serious condition and is an immediate medical emergency for which prompt therapy is essential. While FATE classically affects the limbs, cats may also have clots to their brain (stroke), lungs (pulmonary thromboembolism), heart (myocardial infarction), gut (mesenteric clot) or in other locations.
All cats are at risk of developing heart disease; however, some breeds are at higher risk. These include the Ragdoll (and related breeds), Maine Coon, Sphynx and Rex breeds. Cats eating poor-quality, taurine12 PETS CAT CARE GUIDE 2018 WWW.PETSMAGAZINE.CA HEART DISEASE IN CATS BY KATHLEEN CAVANAGH, DVM >> GUIDE TO CAT CARE PHOTO: DEPOSITPHOTOS.COM deficient diets are also at higher risk for DCM. Congenital heart issues are uncommon in cats, but may include valve stenosis or insufficiency, patent ductus arteriosus (PDA), tetralogy of Fallot and others.
For most cats, not much can be done to decrease the risk of heart disease, though careful monitoring is recommended to allow prompt intervention.
While obesity is associated with many illnesses in cats, there is no evidence it predisposes to heart disease (cats do not get coronary artery disease like humans). Some infections (such as dental infections) may slightly increase the risk of endocarditis (infection of the heart), though this is not common.
Careful history taking and physical exams form the basis of diagnosis of heart disease. The examination will include listening carefully to the heart and lungs and checking for normal pulses.
The veterinarian will endeavour to rule out other diseases that may resemble heart failure, including pneumonia, asthma, cancer, trauma or other concerns. Cats having signs of blood clots may be confused with cats having other conditions, such as brain disease, muscle or skeletal disease or other conditions based on the location of the clot.
Chest X-rays are frequently recommended as a first diagnostic step if the cat is stable. The X-rays may show heart disease definitively, but more often are used as one part of a multi-step diagnostic process. Blood tests may be needed to rule out other conditions. Some specific tests (such as ntpro-BNP) may be useful in determining if heart disease is present. Electrocardiography (ECG) measures electrical signals through the heart and is useful for further evaluating arrhythmias.
The best way to determine the type and extent of heart disease is with echocardiography (ultrasound of the heart). This test is minimally invasive and usually does not require sedation. It allows images and videos of the heart to be collected and analyzed. This may be done by a cardiologist, veterinarian or skilled ultrasound technician and may be analyzed in house or sent away. While it may be more expensive than other tests it usually gives the most information.
MANAGEMENT AND TREATMENT
Heart disease in cats is rarely curable, with very few exceptions. Few surgical management options exist and the focus is medical therapy. There is little proof that therapy before the onset of CHF is effective at slowing the progression of disease in most conditions, though some potential therapies exist. Blood thinners may be used to prevent clots in cats with known heart disease, antiarrhythmic may be used if an arrhythmia is present, but other drugs are likely of limited effectiveness.
As discussed, taurine supplementation may be used in cats with taurine-deficient DCM, but this is very uncommon in Canada. It is not effective for other forms of heart disease.
In an emergency situation, cats with CHF may require oxygen therapy, diuretics (medications that increase the amount of water and electrolytes expelled in urine), chest taps (removal of fluid from around the lungs) and more aggressive care in some cases. Cats with blood clots will require pain control medication, anticoagulants and aggressive hospital care.
After initial stabilization, cats with CHF will almost always be treated with furosemide (a diuretic) to keep fluid off the lungs. They may also be treated with beta blockers (such as atenolol) to slow the heart rate and reduce certain symptoms, ACEinhibitors to help decrease fluid buildup, blood thinners to prevent clots or one of several other medications based on veterinary recommendations.
The prognosis for most cats with CHF is very guarded. Most cats can be stabilized through an initial crisis, but some do not survive initial hospitalization. After leaving hospital, most cats survive for three to six months with therapy. Some rare cases have been known to go into remission, usually young cats that experience CHF after a stressful event, but this is not common.
The prognosis for FATE is much more guarded, especially if severe signs are present. Many cats with saddle thrombosis (clot stuck at the junction of hind limb arteries) do not survive hospitalization, though some may recover fully. Treatment with a blood thinner, such as clopidogrel (Plavix®), is generally lifelong.
Consult your veterinarian immediately if you suspect your cat has heart disease. Prompt workup and therapy may improve prognosis.
Talk to your veterinary healthcare team for more information about heart problems in cats, especially if you own a breed known to be prone to cardiomyopathy.
Kathleen Cavanagh, BSc DVM MET, Consulting Online Editor, Canadian Veterinary Medical Association; Matthew Kornya, BSc, DVM, Resident ABVP, Consulting Editor