Cardiomyopathy in cats comprises an incompletely understood group of diseases. The term cardiomyopathy means heart muscle disease, and encompasses multiple different types. The most common and extensively studied kind that is diagnosed in cats is hypertrophic cardiomyopathy (HCM), and is not the focus of this discussion. The other cardiomyopathies include dilated cardiomyopathy, restrictive cardiomyopathy, and unclassified or ischemic cardiomyopathy. It is unclear what role myocarditis/endomyocarditis (inflammation of the heart muscle) plays in the development and/or exacerbation of cardiomyopathy in cats.
Dilated cardiomyopathy (DCM) in cats is characterized by dilation of the heart chambers with a decrease in the muscle pump function. The left side of the heart is most commonly affected, and mild mitral valvular insufficiency may result. Most cats with DCM come to the veterinarian with signs of congestive heart failure. Affected cats often become withdrawn, stop eating, may have difficult or labored breathing or in some cases can be limping from a stroke. Taurine deficiency is a well-described potential cause of reversible DCM in cats, and should be suspected in cats being fed an exclusively dog-food, vegan or vegetarian home-cooked diet. Cats eating a commercial diet are highly unlikely to be taurine-deficient. Most cases of feline DCM diagnosed have no identifiable underlying cause (idiopathic), and are presumed to be the result of one or more genetic mutations.
Restrictive cardiomyopathy (RCM) in cats is idiopathic in origin, may involve the heart muscle or the interior lining of the heart muscle, and is usually associated with severe secondary heart chamber enlargement. The muscle of the heart becomes infiltrated with scar tissue, making it stiff and unable to relax normally. This in turn leads to high pressures within the heart chambers and secondary heart chamber enlargement develops over time. Cats with RCM typically come to the veterinarian in congestive heart failure with symptoms associated with fluid in the lungs or in the chest and they may also have strokes.
Unclassified cardiomyopathy (UCM) is cardiomyopathy that doesn’t fit neatly into the categories of hypertrophic, dilated or restrictive cardiomyopathies and may have features of some or all of these. Ischemic cardiomyopathy is often lumped into this category as well. When the heart muscle itself is starved of oxygen due to a blockage in blood flow (ischemia), this results in infarction (“heart attack”), though most cats don’t show signs of chest pain. Many cats with end-stage heart disease of any cause may develop myocardial infarctions, leading to a diagnosis of UCM.
Diagnosis of feline cardiomyopathy is typically made via echocardiography (ultrasound of the heart). A blood test called serum NT pro-BNP level may be abnormally elevated and prompt further investigation (echocardiography). Chest x-rays may show heart enlargement, congestion, fluid in the lungs (pulmonary edema) or fluid in the chest (pleural effusion). Electrocardiography (EKG) may show early beats or tachycardia (fast heart rate).
Treatment is directed at controlling fluid retention and improving muscle pump function. Emergency treatment may include oxygen administration, chest taps (thoracocentesis), injectable diuretic, topical nitroglycerin and/or other medications. Chronic oral therapy may include drugs like furosemide, enalapril, pimobendan, digoxin, clopridogrel or aspirin. Abnormal heart rhythms (arrhythmias) may warrant treatment with other drugs (antiarrhythmics).
The prognosis is generally determined by response to treatment and the presence of other problems (kidney issues, cancer, etc.). Generally speaking, uncomplicated congestive heart failure secondary to cardiomyopathy in cats can be expected to have a survival time of 1-2 years with lifelong medication. That said, some cats do poorly, and only survive for a few months. Some cats may live for 4-6+ years following an initial episode of congestive heart failure. Consultation with a veterinary cardiologist is recommended for cats with cardiomyopathy.