Category: heart diseases

Congenital defects are caused by abnormal development of the foetus and disease is present from the time that the animal is born. However, although the disease is present from birth, signs may not be noticed until later in life. Congenital defects can occur in any part of the body and the heart is no exception. The heart is a complicated structure and as it develops there are many things that can go wrong.

Around 1 in 200 dogs have a congenital heart problem. No-one knows why the heart develops abnormally in some animals. It is probably usually the result of a combination of environmental conditions and genetic factors. Some diseases are more common in particular breeds and so it is likely that they are partly passed from parents to offspring. For this reason animals with congenital diseases should not be allowed to breed.

There are a number of congenital heart diseases and some of these more commonly affect some breeds of dogs than others. The diseases are caused by abnormal development of the blood vessels (abnormal connections or narrowing), the valves or as a result of abnormal connection between different parts of the heart (hole in the heart).

The most common forms of congenital heart defect include PDA (patent ductus arteriosus) where there is a communication between blood supply into and out of the heart; narrowing of the large blood vessels taking blood away from the heart – to the lungs (pulmonic stenosis) or to the body (aortic stenosis). Sometimes there is abnormal development of the valves between the various chambers of the heart usually affecting the mitral valve (mitral dysplasia). It is rare for dogs to have a ‘hole on the heart’.

If your vet detects a heart murmur on examination they will need to do further tests in order to find out what is causing the problem. X-rays might help but ultrasound will be needed to find out exactly what is wrong with the heart. Your vet may need to refer your pet to a vet who specialises in heart disease for detailed examination. This will allow the best treatment plan to be formulated.

Unfortunately the long-term outlook for animals with severe congenital heart disease is usually not good. The only cure for heart defects is surgical correction. Some defects can be corrected by an operation, for example to tie off an abnormal blood vessel – for other defects there is no specific treatment.

In cases of pulmonic stenosis it may be possible to reduce the narrowed valve by stretching it using a special catheter (balloon valvuloplasty). In some cases animals have no problems with their disease and can live with the condition.

If animals develop heart failure then this can be managed with drugs to control signs.

If your pet can have surgery to correct their heart defect they will probably need to be sent to a specialist surgeon. However recovery from the operation is usually rapid and they may be back to normal in a week or two.

Unfortunately if there is no surgical option for your pet then they may need drug treatment for the rest of their life. It can be very distressing to watch a young animal suffer with heart disease and, if there is no treatment for your pet, you should discuss with your vet whether euthanasia might be the kindest option.

There are a number of breed testing schemes which allow early detection of these conditions. The following breed clubs operate heart testing schemes:

• Boxer: aortic stenosis
• Bull terrier: aortic stenosis and mitral dysplasia
• Cavalier King Charles spaniel: mitral valve disease
• Great Dane: dilated cardiomyopathy (DCM)
• Irish Wolfhound: dilated cardiomyopathy (DCM)
• Newfoundlands: aortic stenosis
• Pyrenean sheepdog: patent ductus arteriosus (PDA)
• Field Spaniel: prevalence of murmur and arrhythmia

Heart testing for the breed schemes can only be carried out by certain specialist veterinary cardiologists. A list of all currently eligible vets (and their contact details) can be found on the Veterinary Cardiovascular Society website: http://www.bsava.org.uk/vcs/.

An appointment can be made with a specialist veterinary surgeon in your area at their practice or, in some cases, the specialist may come to your vet’s practice. Additionally many of the breed clubs arrange for specialists to be available at certain major dog shows – you should contact the individual breed societies for information on this.

There are a number of advantages to the breed club of running these schemes:

• The clubs can identify unaffected (or less severely affected) animals which can then be used for breeding.
• The number of affected dogs in the breed can be calculated so that clubs can monitor whether the disease is becoming more or less common and whether the breeding programmes are working.
• To identify affected animals so that owners and vets caring for these animals can be advised on treatment.

The exact format of the investigation will depend on the individual breed scheme. The three standard tests used for investigation of heart disease are:

Listening to the heart with a stethoscope (auscultation)

Using a stethoscope the vet can identify any heart murmurs and abnormal heart rhythms which may indicate a structural defect in the heart. In many cases detection of an abnormality with a stethoscope will indicate that further investigation is required.

Performing an ECG

An ECG allows monitoring of the heart rhythm and rate. Some breeds of dog, notably boxers and dobermanns, develop heart conditions that specifically affect their heart rhythm. Sometimes your vet will be able to perform an ECG in the surgery but for many conditions it is necessary to fix a mobile device to the dog which is worn for 24 hours or longer the device is then removed and the information sent away for analysis.

Ultrasound of the heart

Specialist veterinary cardiologists can use ultrasound to examine the heart in detail. This can be done in most dogs without any form of sedation or anaesthesia and in some breeds it can be done without clipping the hair. With ultrasound the vet can examine the chambers and valves of the heart to detect any abnormalities in heart development or function.

Screening tests are very sensitive in picking up early changes in the heart. It is quite possible that the vet doing the test will detect an abnormality that will not affect your dog in everyday life (however it still might mean that your dog cannot be used for breeding).

The vet who does the screening will provide a report to your usual vet and any further investigation or treatment will be managed through your own veterinary surgeon. In some cases your vet will want to refer your pet to a specialist veterinary cardiologist for further investigations.

When animals are screened through a breed heart testing scheme the results of the tests will also be sent back to the breed society for them to use in monitoring the health of the breed. This information will always be kept confidential.

For more information, visit: http://www.fieldspanielhealth.co.uk/schemes.htm

Aortic stenosis is a congenital heart defect. Interestingly, the lesion tends to develop within the first 3 months of life after the puppy is born, as opposed to being present at the time of birth. Aortic stenosis occurs when a constricting ring or ridge of tissue develops directly below the aortic valve, causing an obstruction to blood flow out of the heart. This means that insufficient blood flow may occur, particularly during exercise or times of stress. It is more commonly seen in certain breeds of dog (Golden Retriever, Boxer, German Shepherd Dog, Newfoundland, Rottweiler).

Since the heart has to work harder to pump blood through a narrowed exit the muscles of the heart get larger (hypertrophy). The hypertrophied heart muscles can become deprived of normal blood flow and oxygen, and this can result in abnormal heart beats and dysrhythmias. This may further reduce the ability of the heart to provide the body with an adequate blood supply. Fainting is caused by an insufficient blood supply to the brain.

Although the condition is present shortly after birth, signs may not be noticed until later in life. Many dogs with aortic stenosis have no outward signs of illness. More severely affected animals may be reluctant to exercise, or may faint without warning (especially when excited or exercising).

If the condition is left untreated animals may develop heart failure and signs of breathlessness or coughing may occur. Sudden death may occur in young dogs (less than 4 years of age) with marked to severe disease.

If your vet hears a murmur when listening to your dog’s heart they will want to do some other tests. Heart murmurs are caused by the sound of abnormal and high-speed blood flow and are very common findings in dogs with subaortic stenosis. Very quiet heart murmurs can be present in an otherwise healthy pet so a diagnosis of subaortic stenosis or other congenital heart disease is not necessarily inevitable.

Ultrasound is the method of choice for finding the cause of a heart murmur. If a heart murmur is heard, an ultrasound examination is recommended. Ultrasound examination of the heart requires considerable knowledge and experience and should be performed by someone with experience in examining young dogs.

X-rays are important in the diagnosis and monitoring of heart disease but will not identify the cause of a heart murmur. X-rays are used to see if signs of heart failure are present, if there any signs of further heart damage treatment should be started immediately.

If the aortic stenosis is mild your dog could lead a normal life without treatment. However, in severe cases the outlook is poor. Dogs with significant signs of disease, eg collapse or breathlessness at an early age are likely to require lifelong medication and have a significantly reduced lifespan. Your vet will discuss the outlook and long term management of your dog with you.

In mild cases, it is not necessary to treat aortic stenosis and affected animals will often live a normal life. If disease is severe or if clinical signs are apparent then treatment will usually be prescribed. Your veterinarian may prescribe drugs to reduce heart rate and minimize abnormal heart rhythms. If heart failure is present, your vet may suggest drugs such as diuretics, or ACE inhibitors to reduce fluid build up. You may be advised to restrict your dogs exercise.

Surgical procedures are available and some dogs may be suitable for a balloon valvuloplasty (when a catheter with a balloon tip is inserted into the obstructed blood vessel and the balloon inflated to open the artery). These procedures may improve or resolve clinical signs in some dogs but are not without risk.

Many animals with mild aortic stenosis live a normal life with no signs of heart disease. Severely affected animals are at risk of sudden death or development of heart failure and quality of life may be reduced in these animals. Approximtely 75% of dogs with severe disease will die suddenly from abnormal heart rhythms before the age of three.

All dogs with subaortic stenosis are at risk for development of infections on the heart valves (infectious endocarditis), and prophylactic antibiotics should be routinely administered during surgical or dental procedures, or with any other condition that may predispose dogs to infection.

Affected dogs and their parents (who could be genetic carriers of the condition) should be not be allowed to breed.