Overview of Feline Restrictive Cardiomyopathy (RCM)
Restrictive cardiomyopathy (RCM) is a heart condition that primarily affects cats. It is characterized by a variety of abnormalities, including thickening or dilation of the main pumping chamber of the heart (the left ventricle), dilation of the atria (the uppermost chambers of the right and left sides of the heart), and/or scarring of the lining of the heart. The internal scarring makes the left ventricle less distensible than normal. Together these factors may lead to chronic pulmonary hypertension (high blood pressure in the lungs) and thus to progressive enlargement of the right side of the heart.
Below is an overview of Restrictive Cardiomyopathy in Cats followed by in-depth information about the causes, diagnosis and treatment of this condition.
Restrictive cardiomyopathy can, in severe cases, cause heart failure when fluid accumulates in the lungs. Blood clots, too, can form in the heart and travel to distant blood vessels obstructing blood flow to one or more limbs, especially hind limbs. RCM can be mild to life-threatening.
Most affected cats are usually seven years of age or older, but cats of any age may be affected.
The main causes of RCM are genetic. Factors that may precipitate heart failure and/or difficult breathing in RCM affected cats include: fever, infection, stress (a veterinary visit, physical restraint), and anesthesia. In some cases, restrictive cardiomyopathy is associated with advanced hypertrophic cardiomyopathy.
What To Watch For
Noisy, difficult, open-mouthed breathing
Sudden inability to use one or more limbs
Odd posture of squatting or lying with chest down, head extended and elbows pointed outward
Lack of appetite
See your veterinarian immediately if you see these signs.
Diagnosis of Restrictive Cardiomyopathy in Cats
Diagnostic tests are needed to diagnose RCM and exclude other diseases:
Complete medical history and physical examination, including auscultation of the heart and lungs using a stethoscope
Echocardiogram (ultrasound examination of the heart) – a painless procedure in which a probe is held against a prepared area of the chest wall. The image generated confirms or refutes a provisional diagnosis of RCM.
Electrocardiogram (EKG)-a tracing derived by amplification of the minutely small electrical impulses normally generated by the heart.
Blood tests to evaluate your cat.
Treatment of Restrictive Cardiomyopathy in Cats
There is no recommended treatment for mild, asymptomatic cases, but regular follow-up visits with your veterinarian are vital. In more advanced cases, your cat may have to be admitted into the veterinary clinic and may have to stay there for several days for initial treatment and monitoring. Severe cases of restrictive cardiomyopathy are life-threatening.
Home Care and Prevention
Give any prescribed medications as directed and observe your cat’s breathing pattern regularly to ensure that respiration is quit and uncompromised. Learn to take your cat’s heart rate, record the results, and relay this information to your veterinarian.
Minimize stressful situations. Affected cats are best kept as indoor-only pets.
This disease is thought to be genetic; therefore, there is no preventative care other than not breeding from cats with RCM.
In-depth Information on Restrictive Cardiomyopathy in Cats
Cardiomyopathy means disease of heart muscle. Some, but not all, cardiomyopathies have well defined causes. Symptoms of cardiomyopathy are not specific and many heart and lung diseases produce clinical signs similar to RCM. Diagnostic tests are required to differentiate RCM from other conditions that have similar clinical signs. Below is a list of such conditions:
Hyperthyroid heart disease (caused by excessive activity of the thyroid gland)
Hypertensive heart disease (caused by high blood pressure)
Feline hypertrophic cardiomyopathy
Feline dilated cardiomyopathy
Congenital heart disease
Moderate to severe anemia (low red blood cell count; anemia can cause heart enlargement and/or failure in cats with heart disease)
Over-infusion of fluids (fluid therapy can cause heart failure in cats with heart disease)
Primary pericardial diseases (diseases of the sac enclosing the heart and roots of the greater blood vessels)
Excess growth hormone
Mediastinal mass (a mass in the space between the membranes encasing the lungs and lining the thoracic cavity).
Diagnostic tests are essential for identifying RCM. Tests may include:
Complete physical examination and medical history review. This includes examining the chest with a stethoscope.
Chest X-rays show abnormalities in the size and shape of the heart, identify fluid in the chest, and exclude other causes of difficult breathing, such as pneumonia, asthma, or tumors.
An electrocardiogram (EKG) – a recording of the heart’s electrical action to screen for irregular heart rhythms and/or assist in identifying heart enlargement.
Thyroid test – especially in cats over seven years of age to detect thyroid tumors.
Arterial blood pressure measurement – to rule out hypertension (persistently high blood pressure) as a cause of abnormal heart findings.
A complete blood count – to recognize anemia (low red blood cell count) as a possible factor
Blood tests that test organ function and blood electrolytes (blood particles capable of conducting an electric current), such as potassium, are especially important in severe cases of heart failure, clot formation, or when there are complications involving other body systems.
An echocardiogram (ultrasound of the heart) is the definitive diagnostic test required to establish proper diagnosis of RCM, after excluding other causes of heart enlargement. A veterinarian with skills in this area, or a specialist in cat heart disease, is best qualified to administer this test and draw conclusions from it. “Echo” is often a referral procedure.
No treatment may be recommended for mild, asymptomatic cases of RCM, but regular veterinary follow-up is essential.
Hospitalization is often recommended in severe cases of RCM in which congestive heart failure (fluid accumulation in lung or chest cavity), abnormal heart rhythm, blood clots, kidney failure, and/or low blood pressure/shock are present.
Oxygen, diuretics and/or nitroglycerine ointment may be given for initial treatment of congestive heart failure.
Tapping abnormal fluid accumulations (thoracocentesis) from the chest cavity is required when intrathoracic fluid interferes with breathing.
Blood clot complications need to be treated with additional medications (for pain and clot control). (NOTE: Clot-busting drugs (TPAs) have been effective in cats, but have very serious side effects.).
Dietary modification is sometimes recommended in cats with heart failure (e.g. sodium-restricted “prescription” diet).
Diltiazem (a calcium channel antagonist) may be used, but its use is controversial in restrictive cardiomyopathy.
Enalapril or benazepril (to reduce blood pressure) can be useful in cats with heart failure to reduce the activity of harmful hormones and reduce sodium retention.
Diuretics – reduce fluid accumulation by promoting urinary water loss
Nitrates (topically applied with a gloved hand to a relatively hairless area, such as the inside of the ear) – for home use if breathing difficulties arise at home; the last dose should be wiped off before the next dose is applied.
Aspirin or Coumadin for high-risk clot-formation cases
Follow up Care for Cats with Restrictive Cardiomyopathy
Optimal treatment for a pet with RCM requires both home and professional veterinary care. You should administer prescribed medications as directed and alert your veterinarian if you have any difficulties in this respect.
The details of veterinary follow-up depend on the severity of your cat’s condition, his response to therapy, your veterinarian’s recommendations, and your views. A typical schedule involves follow-up veterinary visits every 6 months. Recheck examinations may be scheduled more frequently at first to monitor your pet’s initial response to therapy.
Follow-up may include:
Chest X-rays to monitor response to therapy
Blood sampling to monitor the effect of drugs on your cat’s kidneys and his electrolyte levels (potassium, for example)
Blood pressure measurements are taken periodically in cats receiving diuretics or ACE inhibitors, like enalapril or benazepril (which both reduce blood pressure).
Echocardiogram is performed initially and then repeated periodically (e.g. 3 to 6 months after diagnosis, and then after 9 to 12 months).
Your cat’s condition can change rapidly, and tests to monitor disease progression will influence decisions about therapy and the prognosis.
The long-term prognosis of RCM is guarded and quite variable. Some cats have been managed successfully for over two years, but cats with relentless CHF, blood clots or fluid accumulation in the chest cavity have a poorer prognosis. Unfortunately, some affected cats die suddenly.