Heart disease in cats: the subtle signs you shouldn’t ignore

Summary

Cardiac disease: the silent killer

Heart disease can be broadly defined as any abnormality of the heart, and includes a wide range of conditions, from congenital abnormalities to functional, structural, or electrical abnormality of the heart.

Heart disease can affect any of the components of the heart, including the external heart sac (the pericardium), the actual heart muscle (myocardium) and the inner layer of cells (endocardium).

Feline heart disease can be a silent killer, because many cats showing few signs until it’s advanced. Studies suggest around 15% of cats may have hypertrophic cardiomyopathy (HCM), the most common feline heart disease.

Quick check: could your cat be struggling?

Book a vet check if you notice new or unexplained:

• Tiring more easily / less play than usual

• Weakness, lethargy, or fainting

• Faster breathing at rest

If you see any of the signs below, go to an emergency vet urgently:

• Open-mouth breathing or panting (clear distress sign)

• Collapse

• Sudden hind-limb weakness/paralysis or dragging back legs

The heart of the matter

The heart and blood vessels (arteries and veins) are part of the cardiovascular system. The heart is a hollow, muscular organ which in cats and other mammals is divided into four chambers. There are two upper chambers, called the left atrium and right atrium, and two lower chambers, called the left and right ventricles.

The heart’s function is to pump blood around the body: the right side pumps blood to the lungs and the left side pumps blood to the rest of the body. A series of valves maintain blood flow in one direction through the heart.

What is hypertrophic cardiomyopathy (HCM) in cats?

Cardiomyopathy is a term used to describe diseases of the heart muscle. In cats, three types of cardiomyopathy have been identified: hypertrophic, dilated and restrictive cardiomyopathy. The most common heart disease in cats is hypertrophic cardiomyopathy (HCM). It is estimated that 60% of cats with heart conditions have hypertrophic cardiomyopathy.

In cats with HCM, the heart muscle becomes thicker than normal, so the heart can’t relax and fill properly. Over time, this can lead to fluid build-up (often in the lungs), blood clots, or sudden death.

Hypertrophic cardiomyopathy has been associated with a genetic mutation in Maine Coon and Ragdoll cats, and a genetic predisposition is suspected in other breeds and mixed breed cats. Middle aged (5 to 7 years) cats are typically affected, however, the disease may develop at a young age or advanced age in some cats. Males are more likely to be affected than females.

A smaller number of cats will have dilated cardiomyopathy, in which the heart muscle becomes thinner and the heart becomes enlarged, affected its ability to contract.

Dilated cardiomyopathy used to be the most common heart condition affecting cats prior to supplementation of taurine in cat diets, but is now more commonly associated with heart disease in dogs.

Also less common is restrictive cardiomyopathy, in which the heart walls are stiffer than normal, and unclassified cardiomyopathy. Some cats will have an intermediate form which can be a combination of the above forms.

What is a heart murmur in cats?

A heart murmur is an extra vibration in the heart beat, which may be detected by the vet during a physical examination. Heart murmurs are heard when there is a disturbance in the blood flow in the heart or large vessels exiting the heart.

Heart murmurs are identified in patients with and without heart disease. Many murmurs are innocent, particularly the soft murmurs identified in young kittens without any evidence of cardiac disease, and these usually disappear on their own.

Pathologic murmurs often have very characteristic sounds (such as a ‘gallop’ sound) and are associated with structural heart disease. Unfortunately many cats with heart disease will not have any abnormalities on listening to their heart.

Other benign murmurs are sometimes discovered secondary to anaemia (decreased red blood cell count), pain, and intense excitement. Heart murmurs in older cats are generally caused by hyperthyroidism or hypertension.

Expert advice from Dr Felicia:

Heart murmurs are not uncommon in cats when they come to the vet, especially if they are very young, very old, or very stressed. Murmurs are reported in up to 80% of cats with subclinical HCM, compared with 30-45% of healthy cats. Hearting a gallop sound or arrhythmia is a more helpful indicator of significant disease.

What is heart failure in cats?

Heart failure in cats is any heart abnormality or cardiac disease that results in the inability of the heart to pump enough blood to meet the body’s needs. Heart failure is therefore the consequence of severe heart disease, but it is important to know that not all heart diseases lead to heart failure.

A cat showing signs of having too little blood in the tissues to sustain normal function is said to be in low output heart failure. A cat showing signs caused by blood building up in poorly drained organs, is said to be in congestive heart failure.

Congestive heart failure (CHF)

Congestive heart failure (CHF) can be caused by a failure on the left, right or both sides of the heart. It is so named because when the heart is unable to pump enough blood to the organs, fluid builds up, causing congestion of the lung tissue.

CHF can occur at any age, in any breed, and either gender, but it happens most often in middle-aged to older cats. While there are many causes of CHF in cats, it is most commonly the result of hypertrophic cardiomyopathy (HCM).

Cost of heart disorder in cats

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Symptoms of cardiac disease in cats

In the early stages of feline heart disease, there may be no visible signs that there are any problems. Cats generally manage to cope despite the onset of heart disease because of well-developed compensatory mechanisms and by altering their activity levels.

Subtle signs cat owners may notice first:

• Tiring easily, e.g. getting puffed out faster during play
• Sleeping more than usual
• Less interest in jumping
• Fainting episodes or sudden weakness

Expert advice from Dr Felicia:

The most common presenting sign of HCM is laboured breathing, though some cats only show vague signs such as hiding and inappetence.

Signs your cat is struggling to breathe (urgent)

Fluid can build up in or around the lungs as heart disease progresses. Seek urgent care for:

• Difficulty breathing or rapid breathing

• Panting or open-mouth breathing

• Blue/grey gums or tongue

Clot risk: the “sudden back legs” emergency

Heart disease can increase the risk of thromboembolism (blood clots). Urgent signs include:

• Sudden hind-limb paralysis/lameness, cold rear limbs

• Crying/vocalising from pain

Expert advice from Dr Felicia:

Acute paralysis in the hind limbs from blood clots preventing circulation can often be confused by owners for trauma/injury from being hit by a car or even tick paralysis.

Causes of cardiac disease in cats

Primary heart disease in cats is often a hereditary condition passed on from parents or grandparents or a congenital abnormality that is present from birth.

Abnormalities of the cardiovascular system leading to primary heart disease

• Valve disease – the heart valves fail to open or close properly
• Myocardial disease – the heart muscle pumps too weakly or relaxes inadequately
• Arrhythmia – the heart beats too slowly, too rapidly or irregularly
• Vascular disease – the blood vessels offer too great an interference to blood flow
• Cardiac shunts – openings between the left and right chambers of the heart
• Extra-cardiac shunts – abnormal blood flow between the body and the lungs
• Parasitism of the cardiovascular system, e.g. heartworm disease

There are also secondary causes of heart diseases in cats, including:

• Hyperthyroidism – the most common underlying cause of a cardiomyopathy
• Kidney failure
• Dietary deficiency of taurine, an essential nutrient
• Hypertension (high blood pressure)

Does my cat’s weight matter?

Being overweight can predispose cats to a variety of serious health issues, including heart disease.

While ensuring your cat isn’t overweight doesn’t guarantee they won’t get ill, it’s something that you can control at home and can lead to a happier, healthier, and longer life for them.

What will happen at the vet?

Cats do not make things easy for vets! You can help by providing a thorough history of your cat’s health and describing any symptoms that you have noticed.

How vets diagnose heart disease in cats:

1. Listen to the heart for murmurs, gallop sounds, or rhythm changes (arrhythmias)

2. Basic tests (often chest x-rays) can check heart size and look for fluid if breathing is affected

3. Electrocardiogram (ECG) may be used when an arrhythmia is suspected

4. Echocardiogram (ultrasound) is the key test to confirm HCM

5. Blood tests (e.g., proBNP) can help assess whether moderate–severe heart disease is likely

Detection of abnormal heart sounds

By listening to your cat’s heart with a stethoscope, a vet can detect an arrhythmia or a heart murmur up to a year or so in advance of heart disease and there is a 85-90% chance of finding early heart disease in a cat.

The finding of a heart murmur alone is insufficient for determining the presence or absence of heart disease in cats. Even with heart disease severe enough to cause congestive heart failure, only half of affected cats will exhibit heart murmurs. Detecting other abnormal heart sounds, such as gallop sounds and arrhythmias, may be of diagnostic benefit, as these may improve the sensitivity and specificity of the diagnosis.

Electrocardiogram

An electrocardiogram (ECG) is used to assess the heart rhythm if an arrhythmia is suspected. An ECG recording allows examination of the electrical currents in the heart muscles and may reveal any abnormalities in its electrical conduction (which underlies the heart’s ability to contract/beat). While an ECG can help your vet to determine the origin of detected abnormal heart rhythms, it may not be adequate for a definitive diagnosis of feline heart disease.

Echocardiogram

Echocardiography, an ultrasound exam to evaluate heart structure and function, is the most important test for the diagnosis of hypertrophic cardiomyopathy in cats. Echocardiography allows visualisation of the inside of the heart in real time, so that heart chambers and walls can be measured. Left ventricular heart walls that are thicker than 6mm are indicative of HCM.

Radiography

Radiograph imaging (x-rays) is useful for visually examining the heart for enlargement or thickening of the walls, or for thickening of the mitral valve (which controls the flow of blood between the left ventricle and the left atrium).

Unfortunately, radiographs are most effective at identifying changes in severe disease, with mild to moderate heart changes to subtle to identify on x-ray. If a cat has rapid or difficulty breathing, chest radiographs can aid in determining if congestive heart failure is present or some other type of lung disease.

Blood tests

Blood tests can be used to screen for or further investigate heart disease in cats. Biomarker testing is a new frontier in blood testing for assessing the heart; in particular, the proBNP test measures cardiac stretch that occurs with heart disease. A positive result suggests the presence of moderate to severe heart disease, however a negative result may fail to identify mild heart disease.  BNP testing is also useful for testing cats whose family members have been diagnosed with heart disease.

Diagnosing hypertrophic cardiomyopathy (HCM)

An accurate diagnosis of hypertrophic cardiomyopathy is a process of careful elimination. Echocardiography (ultrasound of the heart) is the most important test for the diagnosis of HCM in cats.

Because HCM is inherited in many purebred cats and presumed inherited in mixed breed cats, all cats related to an affected cat should be screened for the disease with echocardiography regardless of whether or not they have a heart murmur.

Expert advice from Dr Felicia:

Sadly, hypertrophic cardiomyopathy is a challenging disease to diagnose in cats as some cats will have no abnormal physical examination findings or history.

Diagnosing congestive heart failure (CHF)

Congestive heart failure is usually diagnosed based on symptoms and physical examination findings, such as the presence of fluid in the lungs detected by a stethoscope. To definitively diagnose CHF and determine its cause, your vet will usually perform several tests, such as:

• Blood and urine tests, including Pro-BNP, complete blood count, biochemical panel, thyroid hormone test, heartworm test, FeLV/FIV test, and urinalysis
• Chest radiographs (x-rays) to assess the heart, blood vessels, and lungs
• An electrocardiogram
• An echocardiogram (heart ultrasound)
• A chest point-of -care ultrasound to evaluate if there is fluid in the lungs or around the lungs (pleural effusion)
• Blood pressure measurements

Expert advice from Dr Felicia:

The challenge of seeing cats with congestive heart failure is trying to determine whether the abnormal breathing is secondary to heart disease or something else (such as primary lung disease). Tests that can help us differentiate include a blood test (pro-BNP), ultrasound and x-rays, but can be difficult to perform in a stressed cat who is in respiratory distress. Sedation and oxygen are key for cats who are in respiratory distress and sometimes the full diagnostic workup may need to come a little later.

High blood pressure and high thyroid concentrations are two conditions which mimic hypertrophic cardiomyopathy and should be eliminated as other possible causes of thickening of the heart walls. Your cat will need to have its blood pressure measured to rule out hypertension, and a blood test for high levels of thyroid hormones (T4). Hyperthyroidism can have similar symptoms as HCM, such as lethargy, short breath, and irregular heart rhythm.

Life expectancy

Hypertrophic cardiomyopathy is usually a slowly progressive disease over years. Many cats with mild HCM can live comfortably with monitoring, and some never develop major complications.

If complications like CHF occur, outcomes vary; some cats respond well to medication and live for a year or more.

Expert advice from Dr Felicia:

HCM has an estimated prevalence of 15% in the general population and even higher in older cats (up to 29%), mostly subclinical. Of these cats, approximately 23% will die in 5 years from cardiac causes, independent of age at diagnosis.

Treatment for cardiac disease in cats

Treatment options for feline heart disease varies depending on which disease is present and how severe it is. Where the heart disease is secondary to another disorder, such as hyperthyroidism or hypertension, treatment of the underlying condition may resolve some or all the heart problems. If the problem is caused by a congenital condition (a heart defect that the cat has had since birth), treatment may be surgical repair. In most cases, however, heart disease cannot be cured. Nonetheless, treatment can almost always help improve quality and length of life.

Treatment of hypertrophic cardiomyopathy in cats

Your cat may be hospitalised for appropriate care, especially if it is suffering from congestive heart failure, which is a common outcome of this disease. In hospital, your cat will be placed in a quiet environment and may receive sedation to minimise stress and oxygen demand. If breathing difficulties are severe they may be given oxygen supplementation.

There are several medications that can be used to treat HCM, depending on the advancement of the disease. Cats where disease has been identified on ultrasound but with minimal left atrial enlargement are considered at low risk of congestive heart failure or thromboembolism. There may be no medical treatment apart from to repeat the echocardiogram in 6-12 months, and track proBNP levels. If your cat has more advanced changes such as left atrial enlargement, anti-thrombotic treatment (e.g. low dose aspirin) will probably be given to reduce the risk of clot formation, even if they do not have obvious signs of heart disease.

Treatment of congestive heart failure in cats

Cats with severe congestive heart failure may require initial hospitalisation and oxygen therapy. If fluid is affecting the lungs or is found in the sac surrounding the heart or the chest cavity, it may need to be removed to improve breathing and help the heart pump more efficiently.

Medications will be prescribed to help reduce fluid build-up, improve heart function and normalise heart rhythms. Most cats with CHF require medications for the remainder of their lives. A low-sodium diet may be recommended to help prevent fluid accumulation. Periodic blood tests, radiographs, and echocardiograms are often needed to monitor treatment success and disease progression.

Ongoing home monitoring

Ongoing at home monitoring is an essential aspect of treatment. Monitoring for breathing difficulties, weakness, lethargy, hind-limb paralysis, and loss of appetite can be extremely helpful for the early detection of CHF. If your vet recommends it, you can track your cat’s sleeping/resting breathing rate at home (your vet will guide you in how to do this).

Lifestyle changes

• Dietary – your vet may recommend a sodium-restricted diet, especially if there is CHF, to reduce blood pressure.
• Environmental  – providing a quiet and safe space for your cat away from other pets and active children is important for its recovery.

In conclusion

Heart disease is the silent killer of cats, and one in six cats can be born with or develop heart disease in their lifetime. There does appear to be a genetic predisposition to feline heart disease, and all cats of all ages can suddenly be affected.

Often there are no symptoms until the disease is well advanced, therefore, the most important thing you can do is take your cat to the vet at least once a year for a heart check that includes listening for murmurs and rhythm changes. Early recognition and treatment can facilitate appropriate clinical management and a long, relatively healthy life.

More information

https://www.vetwest.com.au/pet-library/heart-disease-cardiomyopathy-in-cats

https://www.medvetforpets.com/feline-hypertrophic-cardiomyopathy-hcm/

https://www.petmd.com/cat/conditions/cardiovascular/c_ct_cardiomyopathy_hypertrophic

https://www.msdvetmanual.com/circulatory-system/heart-disease-and-heart-failure/overview-of-heart-disease-and-heart-failure

https://www.cathealth.com/cat-health/cardiovascular/1666-heart-disease-in-cats

https://www.petmd.com/cat/conditions/cardiovascular/c_ct_heart_murmur

http://www.vetstreet.com/care/congestive-heart-failure-chf-in-cats

http://www.pethealthnetwork.com/cat-health/cat-diseases-conditions-a-z/aortic-thromboembolism-cats

http://catdoctor.com.au/cat-health/cardiomyopathy-heart-disease/

https://vcahospitals.com/know-your-pet/rodenticide-warfarin-poisoning-in-cats