Genetic Welfare Problems of Companion Animals

British Shorthair (BSH)

Hypertrophic Cardiomyopathy

Related terms: hypertrophic heart disease, heart failure

Outline: Hypertrophic cardiomyopathy is a disease in which the muscle walls of the heart thicken. In time, this condition leads to heart failure and/or other complications such as increased risk of the blockage of major blood vessels by blood clots. Heart failure causes increasing discomfort and malaise which can occur over a prolonged period and blockage of blood vessels causes severe pain. It is thought this condition is inherited in British shorthaired cats. Affected individuals can be identified using ultrasound scanning of the heart. It is thought that the prevalence of the disease could be decreased by not breeding from affected cats identified in this manner.

Summary of Information

(for more information click on the links below)

1. Brief description

Hypertrophic cardiomyopathy (HCM) is the commonest form of heart disease in cats and British shorthaired cats (BSH) are predisposed to developing the disease (Putcuyps et al 2003, Kittleson 2009, Meurs et al 2009, Meurs 2010). In HCM the thickness of the heart wall increases abnormally (Liu et al 1981). This thickening causes multiple problems and at some stage prevents normal heart function and heart failure develops. Over time, the severity of the heart failure gets worse and death occurs. This either happens suddenly, due to the heart failing to pump blood adequately around the body or from the effects of a thromboembolus (a clot causing blockage of a blood vessel), or more slowly after progressive complications caused by poor circulation and fluid build up in the chest and lungs affecting breathing.

In animals affected with HCM some of the heart muscle cells do not work adequately, probably because of a genetic fault. The normal unaffected heart muscle cells therefore have to work harder to compensate and, over time, they increase in size (hypertrophy). Cats with heart disease, but without heart failure, are likely to appear normal to their owners. Veterinary surgeons may notice abnormalities on examining the cat eg they can hear a heart murmur or an abnormal heart beat or rhythm. Other signs of heart disease and failure can be detected using diagnostic equipment such as chest radiography, electrocardiography (ECG) and, most importantly, ultrasonography.

2. Intensity of welfare impact

The intensity of the welfare impacts of this disease depend on the degree of heart failure and secondary effects that it causes. Most cats with HCM do not have heart failure and have no welfare problems. However, in those with severe and terminal heart failure, the presence of fluid in the lungs (pulmonary oedema), makes breathing very difficult and laboured; a condition that can be assumed to be very unpleasant.

Thromboembolic disease (in which a blood clot forms and blocks a blood vessel), can occur as a consequence of HCM, causing severe pain and distress. It is also difficult to treat and some cats may undergo treatments lasting from days to weeks and may still end up having to be euthanased.

Investigations of heart disease and heart failure often need to be extensive. These procedures may be unpleasant for the cats involved.

Treatment usually requires regular oral medication: often dosing three times a day is necessary. This procedure can cause significant distress for some cats. As the heart disease progresses signs of heart failure usually return despite treatment and severe heart failure occurs which causes an unpleasant death unless the animal is euthanased before this occurs.

3. Duration of welfare impact

Heart failure with episodes of breathing difficulties (that may be alleviated by treatment) often occurs progressively over a period of weeks to months. The welfare impacts vary from mild to severe over this period, depending on the success of treatment and the impact of investigations and treatments on the individual. Some cats live for years on medication after an initial episode of heart failure whilst others die suddenly. Though it can occur at any age, many cats have signs by the time they are two or three years old (Kittleson et al 2004).

4. Number of animals affected

British shorthaircats are known to be predisposed to HCM (Putcuyps et al 2003, Kittleson 2009, Meurs et al 2009, Meurs 2010), however we are unaware of any data on the prevalence of the condition in this breed.

5. Diagnosis

Heart disease is suspected either by the owner noticing one of the signs of heart failure listed (see ‘Clinical and pathological effects’ below) or by a veterinary surgeon detecting a sign of heart disease or heart failure on an examination for another reason or a routine check. The diagnosis of HCM requires the use of ultrasonography.

6. Genetics

The BSH breed is known to have a predisposition for HCM (Putcuyps et al 2003, Kittleson 2009, Meurs et al 2009, Meurs 2010). There is some evidence of the disease running in families in BSH and it is thought to be inherited (Putcuyps et al 2003, Kittleson 2006). The mode of inheritance is unknown; however, one study suggested an autosomal dominant pattern of inheritance (Putcuyps et al 2003) – in which an animal will develop the condition if it only inherits one copy of the mutant gene from one of its parents, as is seen in Maine Coon and Ragdoll breeds of cat.

7. How do you know if an animal is a carrier or likely to become affected?

Currently there is no genetic test for HCM in BSHs. If it is an autosomal dominant condition then any animal that inherits one copy of the mutant gene from its parents will develop the condition and can pass it on to its offspring but any unaffected animals will not do so, as they will not have a mutant copy of the gene. However, it has been suggested that there may be incomplete penetrance, in which case it may be possible for some animals to pass on the abnormal gene without showing signs of the disease themselves. Only kittens with healthy parents should be purchased. Ideally the parents should be screened for HCM using ultrasonography prior to mating.

8. Methods and prospects for elimination of the problem

No genetic test exists for the detection of HCM in the BSH breed. There is a scheme in the UK to eliminate this disease from all breeds of cat with a predisposition to it run by the Feline Advisory Bureau and the Veterinary Cardiology Society. For the BSH breed, the scheme is based on an annual examination and ultrasound scan of the heart, unfortunately the current uptake of the scheme by BSH UK breeders is extremely limited (see http://www.fabcats.org/hcm).

Elsewhere in Europe, screening programmes based on annual ultrasonography are also in operation and these methods have also been recommended in the USA. Cats found on ultrasound to be affected are excluded from breeding programmes. It is thought likely that this method will decrease the prevalence of HCM (Kittleson et al 2004).

For further details about this condition, please click on the following:
(these link to items down this page)

• Clinical and pathological effects
• Intensity of welfare impact
• Duration of welfare impact
• Number of animals affected
• Diagnosis
• Genetics
• How do you know if an animal is a carrier or likely to become affected?
• Methods and prospects for elimination of the problem
• Acknowledgements
• References

1.  Clinical and pathological effects

HCM is the commonest form of heart disease in cats (Tilley & Goodwin 2003). It has been found in over 15% of healthy cats (Paige et al 2009). Cardiomyopathy is disease in which the muscles of the heart become enlarged. The name of the condition is a description of what happens rather than its cause and, in fact, HCM can be caused by various diseases. The main cause in British shorthair cats is unknown but is thought to be a mutated gene/s that directly causes heart muscle to develop abnormally.

The heart is a four-chambered pump which is divided into left and right sides. Each side has two chambers: blood enters into the thin-walled upper chambers (atria) and then flows into the larger, lower chambers (ventricles). The ventricles have thick muscular walls. Between the atria and the ventricles are valves that prevent the backward flow of blood. On contraction, blood is pumped from the ventricles into the major blood vessels. There are also valves at the junction of the ventricles and these blood vessels that prevent back flow.

Figure 1. The four chambers of the heart and direction of blood flow. Note the four valves, which in a normal healthy heart prevent the backflow of blood and the thickness of the heart muscle (myocardium) surrounding the ventricles. (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

The right side of the heart receives blood from the whole of the body, other than the lungs, via the venae cavae. Blood accumulates in the right atrium and during a heart beat, flows through the tricuspid valve into the right ventricle and then as the right ventricle contracts, it is pumped through the pulmonary valves into the pulmonary arteries that take it onto the lungs to take up oxygen.

The left side of the heart receives this oxygenated blood from the lungs via the pulmonary veins. This blood accumulates in the left atrium and during a heartbeat it flows through the mitral valve into the left ventricle. Then, as the left ventricle contracts, it is pumped through the aortic valves into the aorta and onto the other major arteries and around the body to perform all the functions of blood circulation, including delivery of oxygen and nutrients and transport of heat and metabolic products.

As the left hand side of the heart has to pump blood around the entire body, whilst the right hand side only has to supply the nearby lungs, the muscles of the left ventricle have to be much stronger than the right. As strength is largely a function of muscle size the walls of the left ventricle are thicker than the right.

The part of the heart’s relaxation and contraction cycle (that together make up the ‘heart beat’) when contraction is occurring is referred to as systole and the relaxation phase is called diastole. In HCM, heart failure is largely due to an abnormal diastolic phase (Bonow & Udelson 1992).

To co-ordinate contractions throughout the heart there is a pathway for coordinating nerve impulses. This can be damaged in HCM leading to disruption of the control of the heart muscle. 

Figure 2. In a normal healthy heart, nerve signals travel through the heart muscle to stimulate coordinated contractions. However if the muscle tissue becomes thicker, as occurs in hypertrophic cardiomyopathy, the nerve signals are disrupted leading to irregular hearbeats. (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

In HCM the thickness of the ventricular walls is abnormally increased (Liu et al 1981). The heart is a complex organ and this muscle thickening causes multiple problems such that, at some stage, it can no longer function normally. The consequences vary depending on which parts of the ventricles hypertrophy and over what time scale and to what degree, on whether valves are affected, and on the degree to which the blood supply to the heart muscle itself is compromised (Peterson et al 1993, Bonagura 1994). Different manifestations of the disease are outlined below.

Figure 3. Hypertrophy can affect the various areas of the heart muscle, with varying effects and consequences. (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

1. In HCM, the heart is usually able to contract and pump out blood adequately. The problem is rather to do with the ventricles relaxing and filling again. This relaxation is important as it helps to suck the blood from the atria and facilitates their filling. If the ventricle fails to relax sufficiently, there is a backflow problem so that blood cannot enter the heart normally. This is called backward or congestive heart failure. When the left side of the heart is affected this causes fluid to build up in the lungs (pulmonary oedema). When the right side is affected the fluid instead builds up in the body and usually shows as fluid accumulating in the chest cavity (pleural fluid), the abdomen (ascites) or in the body generally (oedema). In each case, the thin-walled atrium becomes affected and stretches (dilates). This causes further problems (see below).
2. As the walls of the heart thicken its valves can become distorted and leak. When the tricuspid and mitral valves are affected, this allows blood to flow backwards into the atria during contraction which causes back pressure and backwards heart failure problems. When the pulmonary and aortic valves are affected, they may fail to open properly and so partially block the outflow of blood. One particular consequence of HCM is called systolic anterior motion of the mitral valve (SAM) (Bonagura 1994). In this, part of the mitral valve (which should only be between the left atrium and the left ventricle) becomes caught up in the flow of blood in the left ventricular outflow path. Cardiologists specifically look for this when assessing the patients using ultrasound as it may be a sign of more severe disease.

Figure 4. Hypertrophic cardiomyopathy with asymmetric septal hypertrophy (ASH) can impact the function of the valves of the heart, leading to the backflow of blood as well as systolic anterior motion of the mitral valve (described above). (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

3. The thickened muscle often contains scar tissue which interferes with the conduction of electrical impulses through the heart and causes uncoordinated contractions (Bonagura 1994). Irregular heart beats can contribute to forward heart failure. Forwards heart failure occurs when the left ventricle provides inadequate blood flow to the body which can lead to weakness, collapse, fainting and sudden death.
4. The heart muscle itself needs a blood supply and this is provided by the coronary arteries. As the muscle thickens its demands for blood may outstrip the supply and sections of the ventricular wall may get insufficient oxygen and die. This causes problems like those of human heart attacks (myocardial infarction) in which the coronary arteries suddenly become blocked (Bonagura 1994). 

There are other important pathological consequences of HCM also (Tilley et al 1977). One is due to the dilation of the atria mentioned above. Because of abnormalities of blood flow and because there may be damage to the atrial linings, blood clots may form. These do not cause problems as long as they remain in an atrium but can do if a piece of a clot breaks off and is carried in the bloodstream until it reaches a narrowing that stops it. Further clotting then occurs at this site and the blood supply to the part of the body supplied by this vessel suddenly ceases, Depending on where this occurs, the consequences can be severe (Bonagura 1994). This is called thromboembolic disease.

The usual cause of HCM in cats (and humans) is a genetic fault that results in some of its heart muscle cells not working adequately due to abnormal protein composition. The normal heart muscle cells have to work harder to compensate and, over time as they work harder, they increase in size. This causes an overall abnormally thick muscle and the consequences listed above.

There is an important distinction between heart disease and heart failure. Heart disease can be present for some time before heart failure occurs. When any of the abnormalities of heart disease listed above are present it may be possible for a veterinary surgeon to detect them. When changes occur to affect the adequacy of the function of the heart then heart failure is present, which can be categorised into forward and backward heart failure. Both may be present.

The body is able to respond to heart disease and to compensate for impending heart failure by various mechanisms, outlined below. Some of these can themselves lead to further problems (Bonagura 1994).

1. When it detects inadequate blood flow from the heart, the body causes the heart rate to increase such that blood supply to the organs is maintained. However, this raised heart rate may further restrict the ability of the ventricles to relax as there is less time for this between each contraction; time in which the ventricles can relax and fill. Increasing heart rate can cause backward heart failure to worsen and eventually the amount of blood that the heart can push forwards around the body also decreases. A further problem is that it is during the relaxation phase that the heart muscle itself receives blood via its coronary arteries so when beating quickly its own oxygen supply can be compromised and heart muscle can die.
2. Inadequate blood flow from the heart also causes the body to react as though there has been a loss of circulating blood volume. Hormones are released in response to this causing fluid retention even though there has been no loss of blood. The amount of fluid in the body thus increases and this is one of the reasons that fluid accumulates in the lungs (pulmonary oedema) or elsewhere in the body (pleural fluid or oedema).

Cats with heart disease, but without heart failure, are likely to appear normal to their owners and will not have any welfare problems at that time (Tilley & Goodwin 2003). An owner might be able to detect a fast and abnormally strong heart beat if feeling their cat’s chest. Similarly, a veterinary surgeon may notice a high heart rate or pulse rate when examining a cat. The heart rate is measured by feeling the heart beat, or, more usually, listening to the heart beating using a stethoscope. The pulse rate is measured by feeling the pulsing of blood flowing through a major artery -in cats, usually the femoral artery in the upper inside leg. In a normal individual the heart rate and pulse rate are the same – each heart beat produces a pulse; but this is not always the case in heart failure – sometimes an ineffectual heart beat occurs that does not generate a detectable pulse. This is called a pulse deficit (Bonagura 1994).

The commonest way for heart disease to be detected in cats is through listening for a heart murmur - an abnormal heart sound - using a stethoscope. It used to be thought that such murmurs occurred in up to 95% of cats with HCM (Tilley & Goodwin 2003) but Paige et al (2009) reported that only 31% of cats with HCM and with no signs of heart failure had an audible murmur. Murmurs are produced by abnormally turbulent blood flow. They usually indicate the presence of a structural abnormality of the heart, for example: an abnormal valve that is allowing backflow of blood, or a bulging part of the heart wall that is causing abnormal flow. On detection of a murmur, further investigations should be carried out to find their cause and to determine the health of the heart (Bonagura 1994). Another change that a veterinary surgeon may detect is a 'gallop' rhythm. This is heard in around 40% of cats with HCM (Tilley & Goodwin 2003). Normally a cat’s heart beat has two sounds, “lub – dub”. With gallop rhythm three sounds are heard and this is a reliable indication that heart disease is present (Bonagura 1994). Dysrhythmias such as a gallop rhythm are heard in around 25% of cats with HCM (Tilley & Goodwin 2003).

Other more sophisticated methods of detecting heart disease involve the use of radiographs, electrocardiographs and ultrasound. Radiographs of the chest may show evidence of heart enlargement but this is a relatively crude method. (Chest radiographs are very useful for detecting common signs of heart failure – see below). A disadvantage of chest radiographs is the need for a general anaesthetic.

Electrocardiography (ECG) records the electrical activity of the heart as it beats. This usually can be carried out in cats without sedation or anaesthesia and can provide information about the presence of heart disease. The most powerful tool for examining the heart is ultrasonography. This enables measurement of the thickness of the heart muscle; the size of each chamber and the position and movement of each valve.

Heart failure occurs when there are complications of heart disease affecting other organs (eg the lungs or brain) that can be detected clinically or that cause changes to the cat’s behaviour. There are several quite different ways that heart failure due to HCM can become apparent to an owner (Tilley & Goodwin 2003) as outlined below.

1. There may be decreased activity and appetite, caused by heart failure may be because of fluid build up in the chest cavity or in the lungs or because the heart is unable to supply enough blood to the major organs (backwards or forwards heart failures). In this case the gums and other mucus membranes will eventually look cyanotic (blue) rather than the normal pink (Bonagura 1994).
2. There may be breathing difficulties due to backward left sided failure. Blood that cannot get into the small, stiff-walled left ventricle pools in the left atrium, causing it to dilate, and also causing increased pressure in the pulmonary veins which carry blood from the lungs. As back pressure increases, fluid builds up in the lungs and in the cavities that are normally air-filled. Often owners will only notice breathing difficulties when signs become severe and breathing is rapid or the cat is panting (breathing with their mouth open). Unlike dogs, cats do not pant unless distressed. Cats showing this need immediate veterinary attention. At this stage, investigations will usually find that large parts of the lungs are full of fluid (pulmonary oedema) and/or that the lungs are being compressed by large volumes of fluid trapped between the lungs and the chest wall (pleural fluid). This fluid causes some cats to cough and this may be the first sign of heart disease and failure that an owner notices (Bonagura 1994).
3. The disease may become apparent as a result of a thromboembolus (Tilley et al 1977). As outlined above, a clot formed in the left atrium may detach and cause blockage and blood loss to a distant part of the body. The commonest place for such blockage to occur is at the end of the largest artery, the abdominal aorta, where it splits into three to supply blood to each hind leg and the tail. Affected cats suddenly have severe problems with both back legs; often being completely paralysed. This condition is very painful and the cat will be extremely distressed, usually crying out.
   
   Embolisms can occur anywhere and, if in smaller vessels, may not be detected. Other common sites of major embolisms are the right front leg, causing pain and paralysis; the kidneys, causing acute kidney failure; the small intestine, causing death of a section of bowel, abdominal pain, anorexia (stopping eating), vomiting and, without treatment – death; and in the brain causing a stroke-like episode, the signs of which depend on where in the brain the blockage occurs (Bonagura1994).

Clots can also form in the right atrium and if these detach they cause blockages in the supply of blood to the lungs (pulmonary embolism). The signs of these vary but they can cause breathing difficulties and shock.

1. The disease may become apparent because of fainting due to severely abnormal heart beats. Irregular heart beats may at times fail to supply enough blood to the brain and other organs (Bonagura 1994).
2. As forward heart failure becomes worse and blood supply to the heart itself is inadequate, heart rate may drop and become subnormal. At this stage circulation throughout the body is severely compromised, fluid may build up in the lungs (pulmonary oedema) and in body cavities (pleural effusion in the chest and ascites in the abdomen) and in peripheral tissues (oedema seen mostly in the lower parts of the body – the legs and lower trunk. Body temperature drops due to inadequate circulation of blood. This process is called cardiogenic shock. Terminally, there is inadequate blood supply to the brain and fits, coma and death occur (Bonagura 1994).
3. Cats with hypertrophic cardiomyopathy sometimes show no signs of illness and even no signs of disease on routine veterinary examinations but can then die suddenly (Kittleson et al 1999). Sudden death can occur because of a large thromboembolus. It can also occur in those cats with particularly thick left ventricular walls in which supply of blood via coronary arteries is inadequate leading to death of a large part of the muscle. This might be associated with a sudden increase in demand for heart activity such as occurs with a stressful event. Sudden death can also happen when a severe dysrhythmia occurs.

So, the signs of heart failure vary considerably (Tilley et al 1977). Many cats will have early heart failure without their owners being aware of it.

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2. Intensity of welfare impact

The intensity of the welfare impact varies greatly with the degree of heart failure and the presence or absence of secondary affects. Most cats with hypertrophic cardiomyopathy do not have heart failure and have no welfare problems. Severe and terminal heart failure has severe welfare implications. Pulmonary oedema, the presence of fluidinside the lungs, causes breathing difficulty and this can be assumed to be very unpleasant.

Thromboembolic disease causes severe pain, distress and paresis (inability to use the hindlimbs normally). It is also difficult to treat and some cats may undergo treatments lasting from days to weeks and may still end up with the cat having to be euthanased.

Investigations of heart disease and heart failure often need to be extensive. As well as repeated clinical examinations, blood tests, ECGs, ultrasound examinations and radiographs, often under anaesthesia, are required to manage these problems. These procedures may be unpleasant for the cat.

Treatments for both forward and backward heart failure are available and usually help to reverse signs of heart failure. Reversing actual heart disease is much more difficult although there is some evidence that the size of the left ventricular wall can be reduced sometimes. Treatment is usually dependant on regular oral medication; for hypertrophic cardiomyopathy this unfortunately often means dosing three times a day, a process which itself can cause significant stress for some cats. As the heart disease progresses signs of heart failure usually return despite treatment and severe heart failure occurs which causes an unpleasant death unless euthanasia is performed early enough.

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3. Duration of welfare impact

Heart failure with episodes of breathing difficulties, alleviated by treatment, often occurs over a period of weeks to months. The welfare impact may be mild or severe over this period depending on the success of treatment and the impact of investigations and treatments on the individual. Some cats live for years on medication after an initial episode of heart failure whilst others die suddenly. The average life expectancy of a group of cats (of various breeds) with HCM was found to be 492 days in one study (Ferasin et al 2003). Tilley and Goodwin (2003) indicated that, in general, cats with HCM and no signs of heart failure have an average life expectancy of five years from diagnosis but this is only three months in those with heart failure.

Cats can develop HCM at any age, from a few months old through to old age. In breeds, such as Maine Coons and BSH, predisposed to developing the condition many affected cats are detected by two to three years (Kittleson et al 2004). In Payne et al’s (2010) study the median age of the cats with HCM was 4.6 years.

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4. Number of animals affected

British shorthair cats are known to be predisposed to HCM (Putcuyps et al 2003, Kittleson 2009, Meurs et al 2009, Meurs 2010), however we are unaware of data on the prevalence of the condition in this breed. It is likely that the prevalence is fairly high if it is an autosomal dominant trait as suggested by one study (Putcuyps et al 2003).

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5. Diagnosis

Heart disease may be suspected either when the owner notices one of the signs of heart failure listed (see ‘Clinical and pathological effects’ above), or by detection of a sign of heart disease or heart failure on veterinary examination for another reason or during a routine check. In continental Europe, some cases of HCM in BSHs may be detected through ultrasonography screening, where it appears to be routine (British Shorthair Breed Advisory Committee 2011). Currently routine ultrasound screening does not appear to be common in the UK.

There are genetic tests for HCM in two other breeds – the Maine Coon and the Ragdoll. However, these tests are not likely to be of any use for identification of the disease in BSHs as different genetic mutations are probably responsible for the disease in different breeds (Meurs et al 2009, Meurs 2010).

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6. Genetics

Hypertrophic cardiomyopathy has been shown to be common and to be familial (ie it runs in families) in various breeds of cats, for example the Maine Coon (Kittleson et al 1999). More recently, genetic defects associated with the disease have been identified in the Maine Coon and the Ragdoll breeds (Meurs 2010). However, affected cats of these breeds have been found which do not have these genetic mutations. In humans it is known that over 400 different genetic mutations can be involved in the development of HCM and it is likely that many genes could be involved in cats also (Meurs 2010).

The BSH breed is known to have a predisposition for HCM (Putcuyps et al 2003, Kittleson 2009, Meurs et al 2009, Meurs 2010) and there is evidence of it running in families (Kittleson 2006, Putcuyps et al 2003). The pattern is suggestive of an autosomal dominant inheritance; HCM has been found to be inherited in this way in Maine Coons and Ragdolls where the disease has incomplete penetrance (Sampedrano et al 2009, Lyons 2010, Wess et al 2010). Kittleson (2006) suggested that the mode of inheritance in BSHs should be assumed to be this until proven otherwise – which means that an animal will have a tendency to develop the condition if it only inherits one copy of the mutant gene from one of its parents, although it may not necessarily do so. Meurs et al (2009) have shown that the genetic mutations which cause the disease in Maine Coon and Ragdoll cats are not the cause in BSHs.

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7. How do you know if an animal is a carrier or likely to become affected?

Currently there is no genetic test for HCM in BSHs. If the mode of inheritance is autosomal dominant with complete penetrance then carriers – animals which can pass on the disease to offspring without developing it themselves – should not exist. However, in other breeds such as the Maine Coon, there is variable penetrance which means that not all cats with the mutated gene develop the disease. Only kittens with healthy parents should be purchased. Ideally the parents should be screened for HCM using ultrasonography. 

Routine ultrasonography can be used both as a way of screening potential breeding animals for the presence of HCM and to investigate for signs of HCM which may be inapparent to owners.

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8. Methods and prospects for elimination of the problem

There are schemes in the UK for the elimination of HCM from the Maine Coon breed of cat, using both genetic testing and annual examinations including ultrasonography of the heart of all animals to be used for breeding. These schemes are organised by the Feline Advisory Bureau (FAB) and the Veterinary Cardiology Society (VCS) (see: http://www.langfordvets.co.uk/lab_pcrnews.htm). This scheme also registers BSH cats that have been found to be free of HCM using annual ultrasound examinations, although no genetic test currently exists for the detection of HCM in the breed. The current up take by BSH breeders in the UK is extremely limited.

Kittleson (2006), in the USA, suggested that all BSHs used for breeding should be screened using ultrasound annually from two years of age (as the disease is unlikely to be commonly detected in the breed earlier than this). Cats found to have HCM should not be used for breeding (Kittleson 2006). We are unaware of a formal breeding scheme in the USA aimed at eradicating HCM. In a draft document, the British Shorthair Breed Advisory Committee (2011) suggested that annual ultrasound screening for HCM has become routine in continental Europe but did not recommend its introduction in the UK. We suggest, however, that it would be a valuable tool in reducing the prevalence of this condition in the UK and worldwide. It is a safe, non-invasive procedure. Kittleson et al (2004) recommended that, at the very least, breeding animals should have their hearts examined with a stethoscope by a veterinary surgeon annually. They recommended that breeders use all available information on the health of their animals in making decisions about breeding (Kittleson et al 2004).

If a significant proportion of the animals of the breed are affected, limiting breeding only to those found to be free of it might significantly narrow the gene pool and increase the risk of other hereditary conditions. Outbreeding with cats of other breeds free of the condition may be required to maintain genetic diversity.

Ultrasonographic screening is currently the best way to detect the affected animals that should not be used for breeding, and would decrease the incidence of the disease if enough breeders undertake it. If a genetic test becomes available, this would be likely to facilitate more rapid progress.

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section and to Stephanie Kaufman for assistance in illustrating it.

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10. References

Bonagura JD (1994) Cardiovascular diseases. In: Sherding RG ed The Cat: Diseases and Clinical Management, 2nd edition. Churchill Livingstone: New York. pp 819

Bonow RO and Udelson JE (1992) Left ventricular diastolic dysfunction as a cause of congestive heart failure. Mechanisms and management. Annals of Internal Medicine 117: 502-10

British Shorthair Advisory Committee (2011) Guidelines for healthy and responsible breeding – draft document. www.britishshorthairbac.moonfruit.com/.../First%20Draft%20v1. 5%20for%20BAC%20WEBSITE%20Password.pdf. accessed 16.6.11

Ferasin L, Sturgess CP, Cannon MJ, Caney SMA, Gruffydd-Jones TJ and Wotton PR (2003) Feline idiopathic cardiomyopathy: a retrospective study of 106 cats (1994–2001). Journal of Feline Medicine & Surgery 5: 151-159

Kittleson MD (2006) British shorthairs – routine ultrasounds? Message Board Discussion VIN Associate 2.1.2006. http://www.vin.com/Members/boards/discussionviewer.aspx?FirstMsg=1&LastMsg=20&DocumentId=3399939. Accessed 16.6.11

Kittleson MD (2009) Feline Hypertrophic Cardiomyopathy--Getting Into the Thick of It American College of Veterinary Internal Medicine 2009 Forum Proceedings. VIN Associate http://www.vin.com/Members/Proceedings/Proceedings.plx?CID=acvim2003&PID=pr04232&O=VIN. accessed 16.6.11

Kittleson MD, Gompf R and Little S (2004) Hypertrophic Cardiomyopathy: Advice for Breeders. On-line – VIN Associate http://www.vin.com/Members/CMS/Misc/default.aspx?id=4891 accessed 16.6.11

Kittleson MD, Meurs KM, Munro MJ, Kittleson JA, Liu SK, Pion PD and Towbin JA (1999) Familial hypertrophic cardiomyopathy in maine coon cats: an animal model of human disease. Circulation 99: 3172-80

Liu SK, Maron BJ and Tilley LP (1981) Feline hypertrophic cardiomyopathy: gross anatomic and quantitative histologic features. American Journal of Pathology 102: 388-95

Lyons L. (2010) http://www.vetmed.ucdavis.edu/Catgenetics/HCM_statement_UCD_Lyons.pdf

Meurs KM (2010) Genetic Screening of Familial Hypertrophic Cardiomyopathy in August JRs ed. Consulatations in Feline Internal Medicine Volume 6 p406-409. Saunders Elsevier: St Louis, USA

Meurs KM, Norgard MM, Kuan M, Haggstrom J and Kittleson M (2009) Analysis of 8 sarcomeric candidate genes for feline hypertrophic cardiomyopathy mutations in cats with hypertrophic cardiomyopathy. Journal of Veterinary Internal Medicine 23: 840-3

Paige CF, Abbott JA, Elvinger F and Pyle RL (2009) Prevalence of cardiomyopathy in apparently healthy cats. Journal of the American Veterinary Medical Association 234: 1398-403

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