Restrictive Cardiomyopathy (RCM) in Cats

Understanding Your Cat's Heart Condition

Restrictive cardiomyopathy (RCM) is a type of acquired (a patient is not born with it) disease of the heart muscle, the hallmark feature of which is a "restricted" ability of the heart's walls to relax. That is, the main pumping chambers of the heart (the ventricles) are unable to adequately open, accept blood from the blood vessels "behind" them, and pass blood along in the forward direction. This stands in contrast to heart diseases in which the heart becomes too weak and cannot contract properly. The cause for RCM is typically unknown, although genetic factors are often suspected.

In severe cases, the end result can be that blood backs up from the heart and this increased pressure causes fluid to leak from blood vessels into the lungs and the chest cavity. This process is called congestive heart failure and is discussed in more detail in a separate information sheet.

How Will My Veterinarian Diagnose RCM?

Heart disease may first be suspected prior to heart failure during routine physical examination, based on detection of a heart murmur (an abnormal "whooshing" sound associated with the normally crisp heart sounds). However, some cats with RCM do not have a heart murmur and many cats with heart murmurs have conditions other than RCM. A blood test called NT-pro-BNP can be used to screen for RCM and other heart diseases in asymptomatic cats.

If congestive heart failure is already present at the time of diagnosis, other physical exam findings may be present, such as rapid and labored breathing. Breath sounds heard with a stethoscope may be either extremely quiet or unusually loud, depending on where fluid has accumulated.

The Echocardiogram: Confirming the Diagnosis

Definitive diagnosis of RCM requires an echocardiogram (ultrasound examination of the heart), during which information is collected about the size, structure, and function of the heart. Specific echocardiographic findings in cats with RCM are variable. The pumping ability of the ventricles often appears normal or nearly normal. However, due to the inability of the ventricles to relax and receive blood from the atria, these weaker chambers behind the ventricles are often enlarged. In some cases, scar tissue can be seen bridging across the left ventricle, contributing to its inability to properly relax.

Additional Tests Your Cat May Need

Several other diagnostic tests may be important during initial and followup evaluation. Chest x-rays provide a "big picture" view of the heart within the chest cavity alongside the lungs. Prior to the onset of congestive heart failure, chest x-rays yield a baseline for future comparison. Once congestive heart failure develops, they comprise the most important imaging test by which medical therapy is monitored.

An electrocardiogram (often called an EKG or ECG) is used to identify and characterize arrhythmias (abnormalities in the electrical activity of the heart). The relative severity of an arrhythmia dictates whether or not it warrants specific therapy. Followup EKGs are instrumental in assessing progression of previously noted arrhythmias and their response to antiarrhythmic therapy.

Finally, blood work may be performed to assess kidney function and electrolyte concentrations, which may be affected by many of the commonly used medications in the treatment of heart disease and heart failure. It is important to monitor these values so that undesirable side effects can be avoided or minimized.

Treatment Options for Your Cat

Unfortunately, as is the case for many types of heart disease in animals and people, no medication has been shown to reliably delay progression of this disease. Therefore, controversy exists over which medication, if any, is most appropriate to use. Some classes of agents which are sometimes prescribed include "beta adrenergic antagonists" (typically called beta blockers), calcium channel blockers, and inhibitors of an enzyme called "angiotensin converting enzyme" (these are called ACE inhibitors).

If congestive heart failure is present, a drug called "furosemide" (often referred to by one of its brand names, Lasix) is used together with an ACE inhibitor, sometimes along with a beta blocker or calcium channel blocker as well.

Because cats with heart disease are prone to forming blood clots within the chambers of their hearts, blood thinner medications will often be used to reduce the risk of this happening. These include options such as clopidogrel (Plavix) and rivaroxaban (Xarelto). Aspirin can also be considered, although this appears to provide minimal reduction in blood clot risk for cats.

What to Expect: Prognosis and Quality of Life

Just as the echocardiographic appearance of RCM varies between affected cats, so does the long-term prognosis. The presence of congestive heart failure does worsen overall prognosis, although many cats respond very well to medical therapy for some period of time. In the absence of heart failure at the time of diagnosis, some cats remain asymptomatic for prolonged periods, although it is impossible to predict how an individual cat will fare.

Critical Signs to Watch For at Home

Once the diagnosis of RCM has been made, it is important to watch for signs of heart failure (the buildup of excessive fluid in the body due to heart disease). Symptoms of heart failure include lethargy, weakness, intolerance to activity or exercise, and rapid or labored breathing. Some cats may only show mild and nonspecific behavioral changes such as hiding or loss of appetite.

Finally, a subset of cats with heart disease form blood clots inside their heart, which can then be released and become lodged in an artery downstream. This can result in a sudden onset of difficulty walking, atypical vocalization, and even sudden death.

Observation of even the milder of these symptoms warrants a phone call to your veterinarian. More severe symptoms, such as difficulty breathing or walking, require immediate attention on an emergency basis.

Living with RCM: A Partnership in Care

A diagnosis of restrictive cardiomyopathy can feel overwhelming, but you're not alone in managing this condition. While RCM is a serious heart disease and the long-term outlook varies from cat to cat, many cats live comfortably for extended periods with appropriate monitoring and treatment. Some cats remain symptom-free for prolonged periods and may never develop issues like congestive heart failure. If the disease does progress to the point of causing symptoms, medications can significantly improve comfort and quality of life. The key is staying vigilant for changes in your cat's breathing, behavior, and activity level, keeping up with regular veterinary checkups, and maintaining any prescribed medications. Your veterinary team is your partner in managing this condition, ready to answer questions and adjust your cat's care plan as needed. By watching for warning signs—particularly breathing difficulties and sudden changes in mobility—and seeking help when needed, you're giving your cat the best chance at a good quality of life.