Heart disease is common in dogs just as it is in people. The most common cause of heart disease in dogs is valvular disease which pre-dominantly affects middle-aged to older small breed dogs.
Diseases of the myocardium (heart wall muscle) such as dilated cardiomyopathy is the second most common cause of heart disease in dogs and is found to predominantly affect middle aged to older large breed dogs.
It is important to realise that in the early stages of heart disease most dogs will have no clinical signs at all. This is because the body has compensatory mechanisms that maintain adequate blood flow through the heart and blood supply to all the body tissues. This ensures oxygen and nutrients are supplied to all parts of the body and carbon-dioxide and waste products can be eliminated.
As heart disease progresses these compensatory mechanisms may eventually no longer be able to cope and progress to a state of congestive heart failure.
What are the symptoms of congestive heart failure in dogs?
- reduced exercise tolerance
- weight loss/muscle wastage
- a distended abdomen
- difficulty sleeping
- coughing (mainly produced when changing position at rest)
- increased rate and effort of breathing
If you notice any of these symptoms, bring your pet in to us as soon as possible.
How will I know if my dog has heart disease?
Heart disease in its early stages will show NO clinical signs.
Regular check-ups at the vet such as the annual vaccination are therefore important as at these check-ups the vet will perform a full examination which will include listening to the heart for any abnormalities such as heart murmurs or arrhythmias (heart rhythm disturbances).
The vet will evaluate the pulse for its quality and strength as well as assessing the gums which can provide information about the blood supply around the body.
What is a heart murmur?
A heart murmur is simply a noise heard by your vet that is caused by turbulent flow of blood through the heart. It is not a disease or a diagnosis as it can have several underlying causes. For instance, a young puppy with a ‘hole in the heart’ will have a heart murmur as blood is being forced through a passage it should not normally be flowing through. Also, a leaky valve where blood is regurgitating back in the wrong direction will cause a heart murmur as will a narrowed blood vessel leaving the heart as blood has to be forced through it and so on.
A heart murmur in some cases may be termed as ‘innocent’ or physiologic. In these cases, there is no underlying disease process and is a normal natural occurrence.
Physiologic heart murmurs are often recognised in very young animals where we may recommend monitoring initially as often the murmur disappears by about 12-16 weeks of age. Deep-chested dogs and very athletic dogs such as grey hounds are also often found to have physiologic heart murmurs.
Finally, a heart murmur can also be caused by diseases not related to the heart. For instance, anaemia (a low number of red blood cells) will ‘thin’ the blood and if severe enough can lead to turbulent flow of blood and a resultant heart murmur being heard.
My dog has a heart murmur. What should be done?
Heart murmurs caused by heart disease will often be identified in pets that are in general good health with no symptoms relating to heart disease in particular. In such cases it is advisable to investigate further to identify the underlying cause for the heart disease. An echocardiogram (ultrasound scan of the heart) is the recommended diagnostic test as it allows us to see right inside the heart! The scan is commonly performed by a specialist and allows assessment of all the structures of the heart and we can therefore find out the cause in most cases. The scan is often performed conscious (although some cases may need sedation if the patient is too wriggly), it is not painful at all, and, it only requires a small patch of fur on the chest to be clipped.
It is important to know that no treatment will be required in many pets with heart disease that are not showing any clinical signs. In some of these cases, based on the current evidence, treatment may be recommended based on the underlying condition.
Other tests may be recommended based on the findings of the physical examination of your pet.
Blood tests may be performed to look for anaemia, or signs of concurrent problems such as kidney or liver disease.
Blood pressure is a very important test that is often recommended in older dogs.
Electrocardiogram (ECG) measures the electrical rhythm of the heart and is performed if an arrhythmia (rhythm disturbance) is suspected.
Radiographs may be performed to evaluate a patient with a cough as the major clinical sign.
You do not have to have all or any of these tests done if you do not want to. Some animals with heart murmurs live a very long time with no adverse effect on their quality of life. Some animals may never be affected by the disease. Unfortunately, we cannot predict which animals will be so lucky just based on the initial examination. It is our job to give you the best advice and offer the best care to our patients.
To do this we need information which is gained by the physical examination as well as by performing these additional tests.
Why is important to monitor my pet's breathing?
A good monitoring tool that is very low tech and free of charge is counting your pet’s sleeping respiratory rate (SRR). To do this you will need to count the number of breaths your pet takes in a minute. It is important to perform the measurement when the pet is completely at rest. It should not be performed after exercise, when your pet is panting, after a meal or, when the pet is dreaming! Simply count the number of times the chest rises in 1 minute and this will be the number of breaths taken in 1 minute. Take 3 readings every evening for a few days to get an average reading.
The reason for measuring the resting breathing rate is that as the heart de-compensates (from heart disease to heart failure) the SRR will increase. This is because fluid starts to pool in the lungs. The SRR has been found to be a very sensitive measure and it allows earlier recognition of disease progression and the need for treatment. The measurement is also useful for monitoring patients being treated for heart failure to assess treatment success as well as deciding when dose changes or additional medications may be required.
Most dogs and cats will have an SRR of 8-24 in a minute and, the aim in most cases is to maintain the SRR below 30. Having a value that is considered normal for your individual pet and monitoring for significant increases is therefore important.
When should I call my vet for advice based on my dog's sleeping respiratory rate?
- If there is an increase from a low value to 30 breaths or more in a minute. Do NOT delay contacting us in this instance.
- If your pet is displaying signs of having difficulty breathing or is coughing excessively. Do NOT delay contacting us in this instance.
- If the SRR drops below 12 in a minute. We may be able to reduce the dose of furosemide (See treatment options below)
How can heart disease in dogs be treated?
Unfortunately, there is in most case no cure for heart disease. Specialist techniques such as valve replacement surgery can be performed in select cases, but these procedures are not yet widely available.
The aim of treatment, therefore, is to alleviate the symptoms of congestive heart failure with medical treatment and fortunately, in many cases a good quality of life can be successfully achieved.
For dogs in congestive heart failure a standard ‘quadruple’ therapy of heart medications is administered. This combination of 4 drugs includes 2 types of diuretics (furosemide and spironolactone) which make the body excrete more fluid by way of urine. This serves the purpose of lowering the blood volume and thereby reduced the amount of blood the heart has to push around the body and, in effect, reduces the workload on the heart. If the blood volume were to remain high and the diseased heart cannot efficiently pump blood round the body and back to the heart, then this blood will pool in the blood vessels and fluid will leak in to the abdomen and chest causing conditions known as ascites and pulmonary oedema respectively.
Pimobendan and benazepril are the other 2 drugs in the ‘quadruple’ therapy protocol. Pimobendan effectively increases the strength of contraction of the heart. Benazepril’s effect is more complicated - In the face of the use of diuretic drugs, the body releases hormones to counter the effect of the increased water loss through urine. This would be counterproductive as conserving more fluid will increase the workload on the heart that the diuretics are trying to reduce. Benazepril works by blocking this counterproductive hormone produced by the body.
There are a number of large-scale veterinary studies that give evidence to the use of heart failure medications. For instance the ‘QUEST’ study demonstrated a very significant increase in survival time for dogs in congestive heart failure treated with Pimobendan. A recent study called ‘EPIC’ has demonstrated a significant survival benefit in treating dogs in ‘pre-clinical’ (no clinical signs) heart disease with Pimobendan. The ‘EPIC’ study only investigated dogs with valve related disease.
Heart disease is progressive and therefore cases will require regular check-ups to assess the stability of the disease and to decide if any changes are required to the treatment plan.
Can heart disease in dogs be prevented?
Unfortunately, in dogs, diet and exercise are not known to lead to development of heart disease as they are in people. Careful management of these aspects is of course important to prevent obesity and in the management of other diseases like arthritis and diabetes mellitus.
The aim for heart disease in dogs is early diagnosis and treatment.
What is the prognosis for a dog with heart disease?
The long-term outlook can vary from being very good with some dogs never being affected by their disease through to poor for some forms of the disease.
Your vet will guide you on the prognosis for your pet based on the underlying condition.
Please speak to one of our vets if you would like more information on any aspect of heart disease in your pet.