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Cardiomyopathies are a group of diseases that affect the heart muscle. They are the most common type of heart disease seen in cats, and are the most common cause of heart failure. In contrast, in dogs and humans the most common form of heart disease is due to disease of the heart valves, but this is rarely seen in cats.

There are a number of classifications of feline cardiomyopathies:

• Hypertrophic cardiomyopathy (HCM): HCM is the most common form and occurs where there is an increase in the thickness of the muscular wall of the heart. This reduces the volume of blood within the heart and prevents the heart muscle relaxing properly between contractions.
• Dilated cardiomyopathy (DCM): In DCM the heart muscle wall becomes thinner than usual, the heart dilates and enlarges, and the thin heart muscle cannot contract effectively.
• Restrictive cardiomyopathy (RCM): In RCM the muscle wall of the heart is replaced with fibrous tissue making it stiff and inelastic, meaning the heart chambers cannot fill normally
• Intermediate cardiomyopathy (ICM) & unclassified cardiomyopathy (UCM): These are cases with changes consistent with more than one type of disease – for example a mixture of both hypertrophy and dilatation present.

What causes cardiomyopathy?

Although in the majority of cases of heart disease in cats the underlying cause is unknown, there are various potential recognised causes, and your vet may need to investigate some of these. Known potential underlying causes include:

• Hyperthyroidism (overactive thyroid glands)
• Hypertension (high blood pressure)
• Acromegaly (excessive growth hormone production)
• Nutritional causes
• Taurine deficiency (causing dilated cardiomyopathy)
• Infiltrative of the heart muscle (such as viruses like FIP)
• Lymphoma (a type of malignant tumour)
• Exposure to toxins
• Some drugs may have secondary effects on the heart
• Hereditary causes
• Genetic defects have been recognised in Maine Coon cats and other breeds that may contribute to development of cardiomyopathy

What are the symptoms of cardiomyopathy?

Many cats with cardiomyopathy do not show any symptoms in the early stage of the disease, and some cats will never develop any clinical signs for life. For some cats, the development of symptoms can be slow and progressive, and in others they can progress quickly.

There is great value in regular vet checks for your cat even if they seem outwardly very healthy because your vet can pick up many subtle signs of disease. We strongly recommend at least annual checks for all cats, with more frequent check for older cats. Early signs of cardiomyopathy that your vet may be able to detect on a clinical examination. which can include:

• Heart murmur – this is an abnormal noise your vet can detect when listening to your cat’s heart with a stethoscope
• Gallop rhythm or arrhythmias – these are abnormal beats and abnormal rhythms of the heart beat
• Abnormalities in heart rate – with heart disease, the heart rate can sometimes significantly increase or decrease outside of the normal range for a cat, and sometimes there may be heart beats without any effective flow of blood (known as a ‘pulse deficit’)

If your vet picks up any of these signs, given that many cats do not show symptoms with early heart disease you may be advised for your cat to have an ultrasound of the heart. This allows detailed examination of the heart anatomy, can assess how the blood flows through the heart and measure for any abnormalities.

Advanced cardiomyopathy can be associated with more obvious clinical signs

• Congestive heart failure – sign of heart failure in the cat include difficulty breathing, more rapid breathing, cold extremities (ears and paws), pale gums, fainting spells (uncommon). Coughing is rarely seen in heart disease in the cat.
• Feline aortic thromboembolism (FATE) – this is a very serious and life-threatening consequence of heart disease. In some cats with heart disease they can develop clots in their heart chambers (usually the left atrium). These clots can potentially dislodge and break away into the circulation where they may block one or more of the main arteries. The most common location for the clot to form a blockage is where the aorta divides to supply blood to the hindlegs. These cats present with a sudden onset of hindlimb paralysis and severe pain. The prognosis for recovery is poor.
• Sudden death – sadly, in some cats this can occasionally be the first presenting sign of heart disease.

How is cardiomyopathy diagnosed?

Heart ultrasound (echocardiography) – gold standard for diagnosis and monitoring as it allows a detailed view of the internal dimensions of the heart, the wall thickness, and the contractility of the heart. It can also show where a heart murmur is originating from. This is the only test which can readily distinguish between different types of heart disease in cats. It is a painless procedure and most cats do not require sedation. We have a registered specialist who comes to the Hospital to perform these scans.

Radiography (X-rays) – are helpful for showing changes in the overall shape and size of the heart, and for detecting a build-up of fluid (pulmonary oedema or pleural effusion). Repeating radiographs may also allow monitoring of the efficacy of any treatment.

Screening and monitoring for potential underlying disease –this can include blood and urine testing, and blood pressure measurement. This is also useful for monitoring for side effects from the medication used to treat heart failure especially with respect to renal function and electrolyte balance.

Electrocardiogram (ECG) – this is an electrical trace of the heart activity. It can be useful for the detection of cardiac rhythm disturbances, but has limited use beyond that.

Genetic testing – there is a genetic screening test for HCM in the Ragdoll and the Maine Coon. Unfortunately, a negative test does not guarantee the disease will not develop in an individual as there are a number of gene mutations that can cause the disease.

Treatment

There are some types of cardiomyopathy where the underlying cause can be treated however this is uncommon. This may include supplementing taurine for DCM, or treating hyperthyroidism or systemic hypertension.

There is no known therapy to prevent progression of cardiomyopathy in cats that are not showing symptoms. When heart failure develops, there various drug treatments may be available to help improve and manage the condition depending on the clinical signs. Not all medications will be suited to each case, and is it important that a specialised plan is formed for each cat.

Medications that may be used include:

• Diuretics (frusemide) – these are extremely valuable medications that help to remove the fluid build-up in or around the lungs. Dosage can be adjusted over quite a wide range depending on response.
• Beta-blockers such as atenolol, which slows down the heart rate and reduce the oxygen demand on the heart. This can be useful if there is “SAM” (systolic anterior motion of the mitral valve) but must be used with caution as they can reduce output from the heart.
• ACE-inhibitors (angiotensin-converting enzyme inhibitors, e.g., benazepril, or ARBs (angiotensin receptor blockers, e.g., telmisartan) – help block the activation of the renin-angiotensin-aldosterone system (RAAS) which is a hormone system stimulated in cats with heart disease. Their use may help in the management of heart failure and possibly also in earlier stages of heart disease.
• Pimobendan – is a calcium channel sensitiser. It increases the strength of the contraction of the heart and acts to dilate blood vessels which may help the flow of blood. It can be helpful for cast with DCM.

Unfortunately, many drugs that are used to treat heart disease lack the large scale clinical trials that exist for humans and even dogs, and we are not always certain there is a proven benefit.

Prognosis for cats with cardiomyopathy

The prognosis for cats with cardiomyopathy is extremely variable, and depends on the type, presence or absence of underlying causes, and rate of progression to heart failure. In many cases, careful use of specific medications for heart failure can significantly improve the cat’s quality of life.

Disclaimer: Please note that the information provided on this page does not replace the advice of your veterinarian. If you are concerned about your cat’s health in any way, we strongly recommend you seek veterinary advice.