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Friday, 9 December 2011

Heart disease and heart failure in dogs and cats

Welcome to PercyPods Pet Emergency blogs. We hope that you and your pets have been well since our last one. This week we are going to discuss heart disease. Heart disease is relatively common in both dogs and cats. Although many of them are affected for many years without ever having a major crisis, some pets can suffer life-threatening problems and so it is important for pet carers to be well-informed about this condition.

What is the heart and what does it do?

Okay so let’s start by considering what the heart is and what it does. The heart lies in the chest cavity and is divided into four chambers. It is made up mostly of muscle and of a number of little valves. Blood flows through these valves which open and close intermittently, a bit like automatic gates; this flow of blood through the valves can usually only occur in one direction and this makes sure that the blood flows around the heart in the right way. The heart acts as a pump which pushes blood around the body. Blood picks up oxygen in the lungs. It flows through the heart and is pumped out to the rest of the body providing an oxygen- and nutrient-rich blood supply to all the tissues and organs, including very important ones such as the brain, the kidneys and the liver. When the blood reaches these organs the oxygen is removed from the blood, along with other very important things such as sugar, and the blood picks up waste substances such as carbon dioxide. The blood then returns back to the heart and flows back to the lungs where the cycle repeats itself. Now the tissues and organs of the body need to receive a good blood supply that contains enough oxygen and other essential substances in order to work properly and stay healthy. In heart disease the heart can start to fail as a pump which means that the circulation is disrupted resulting in widespread and potentially life-threatening consequences.

How can the heart become diseased?

So now that we have considered why the heart is important, let’s look at how the heart can become diseased. As mentioned before the heart is mostly made up of muscle and valves and most types of heart disease in dogs and cats affect one or both of these structures. Diseases that affect the heart muscle mean that the ability of the heart to pump blood is compromised – the pump becomes weaker. Diseases of the heart muscle are known as cardiomyopathies and they occur in both dogs and cats. Some dogs, especially large dogs such as Great Danes and Dobermans, can be affected by a disease known as dilated cardiomyopathy and Boxers are also affected by so-called Boxer cardiomyopathy. There are a variety of different diseases of the heart muscle seen in cats and this type of heart disease is the most common type in cats; a disease known as hypertrophic cardiomyopathy is especially common and one of the main contributory factors for hypertrophic cardiomyopathy is another common condition called hyperthyroidism. Hyperthyroidism is a hormonal disorder that is common in older cats.

The other main group of heart diseases in dogs and cats are ones that affect the valves, the four little gateways through which blood has to flow. When the valves become abnormal the flow of blood through the heart is disrupted and this has a knock-on effect causing changes in the rest of the heart. The valves can become leaky so that blood can flow backwards – remember how we said before that it is important for blood to only flow one way through the heart. The valves can also become narrowed which makes it harder for blood to flow through them. Valve diseases are especially common in dogs and breeds that are commonly affected include the Cavalier King Charles Spaniel, the Yorkshire terrier and the Boxer.

Other types of heart disease that we see in dogs and cats include ones where the heart rhythm becomes very abnormal due to a problem in the electrical system of the heart. As a result, the normal regular beating of the heart is disrupted; this is called a dysrhythmia. Some dogs in particular can also be affected by a condition where fluid builds up in the sac around the heart and stops the heart from filling properly with blood and therefore from pumping properly; this is called a pericardial effusion.

It is important for you to realise that these types of heart diseases in dogs and cats also occur in some humans but they are not the same thing as a heart attack which is something that is in fact thought to be very rare in dogs and cats.

What will I notice if my pet has heart disease?

The next thing to discuss is what you may notice if your pet has heart disease. The first thing to say is that in many cases heart disease is something that affects older animals. However some animals are born with heart diseases or become affected at a young age so the possibility of heart disease cannot be excluded just because an animal is young.

The second thing to say is that we have to distinguish between heart disease of the sort that we have already described and actual heart failure. Many animals are affected by heart disease but cope just fine, often for long periods of time, until eventually the heart becomes too compromised and stops pumping blood efficiently; this is heart failure – in other words heart failure is a consequence of heart disease. Animals with heart disease may not show any signs if the heart disease is mild enough to allow the heart and the rest of the body to compensate for the disease. However, if the heart disease is severe enough that the heart cannot compensate, heart failure will occur and will lead to signs that we will describe shortly.

Having said that many animals that have heart disease have abnormal heart sounds when listened to by your vet using a stethoscope. These abnormal heart sounds are referred to as heart murmurs and they may be detected by your vet when your pet is seen for an annual health check at the time of vaccination or at other times. Finding a heart murmur may prompt your vet to recommend that your pet is examined further for possible heart disease. In this way you can be alerted to the possibility of heart disease in both dogs and cats before it becomes a significant problem.

There are some notable differences between dogs and cats mostly because dogs are usually taken on walks and other forms of exercise when heart disease symptoms may show themselves. Cats tend to exercise away from their owners and so it is not so obvious. This means that heart failure often becomes apparent in cats in much more advanced stages of disease.

In dogs with heart failure, the most common things that you might see are that your dog will be less keen than normal to go out for a walk, they may also seem to get tired more quickly when out exercising, and they may pant more than normal. Another common sign in dogs is coughing, especially after sleep. In more serious cases, breathing may be obviously laboured. Sleep and eating may be difficult for animals in these advanced stages of disease. Other signs that may be seen are that your dog's abdomen or tummy area looks swollen because of fluid accumulating inside it. In other dogs fainting episodes known as syncope may occur.

Usually the signs of heart failure progress slowly so that there is time to get treatment started before the symptoms get too bad. However, occasionally the first thing you will notice is that your dog will be collapsed, struggling to breathe and pale or cyanotic. Cyanotic means that the gums take on a bluish/purplish appearance and this is a life-threatening emergency.

In cats, the signs of heart failure are usually initially quite subtle as cats are very good at adapting their life-styles to suit how they are feeling. It is not common for cats to cough when in heart failure (unlike dogs). Most commonly cats will present as having progressively more difficulty breathing, they may use their abdominal muscles to help them breathe in. Like dogs, they may have difficulty sleeping and eating in the later stages of the disease.

Another relatively common scenario is for a cat to have been completely normal and then suddenly to be found having trouble walking in their back end or to be completely unable to use their back legs. Some of these cats may also be in severe pain and will be yowling or breathing quickly with their mouth open. This happens because in cats much more than in dogs heart disease can cause a blood clot to form in the heart that then dislodges and comes to lie in a position where it cuts off the blood supply to the back legs. This condition is known as feline aortic thromboembolism or saddle thrombus. The clot most commonly gets lodged where it affects the back legs but it can also affect the front legs or elsewhere in the body although this is less common.

In both dogs and cats, the signs of heart failure, especially in the early stages, may be non-specific such as lethargy, weight loss or loss of appetite.

What treatment will my pet need?

So let’s now talk about what treatment your pet will need if he or she is suffering from heart disease. There are basically three different scenarios that might occur. The first is that you will know that your pet has heart disease for a long time and eventually your vet will recommend that he or she is started on some medications. They will continue to work with you to monitor your pet’s progress and adjust the treatment as necessary. The second scenario is when an animal that is already on long-term treatment has a severe acute flare-up in their condition and your vet will have to try and restabilise them. The third scenario is when your pet has shown no prior signs and is suddenly found one day in a very bad way, struggling to breathe and often collapsed.

We cannot be too specific or go into too much detail here but we would just like to mention some of the tests and treatments your pet may need. In terms of diagnosing heart diseases, as mentioned before, the first signal is often an abnormal heart sound or a heart murmur during a physical examination of your pet; sometimes an abnormal heart rhythm can be detected. The main tests that are then used to diagnose heart disease and to assess its severity are x-rays of the chest to examine the heart and lungs and ultrasound of the heart, which is known as echocardiography. An ECG is performed in some cases to check whether the heart rhythm is normal or not and some animals will also have blood tests. These blood tests may include measuring certain markers of heart disease and also for example to check how your pet’s kidneys are working. Measuring thyroid hormone levels may be appropriate in cats.

In terms of treatment, it is important to realise that we cannot actually cure most types of heart disease and treatment is aimed at managing your pet’s problem, basically trying to improve their heart failure so they can enjoy a good quality of life for as long as possible. There are many different drugs that are used to treat heart disease and heart failure in dogs and cats. The medications chosen will depend on the type of heart disease present, the overall health of your dog or cat, and the severity of the heart disease.

Drugs are used to help reduce the workload on the heart so that it can continue to cope for as long as possible. They are also used to try and deal with the consequences of the fact that the heart is not working very well. In particular most animals with heart disease will receive drugs known as diuretics; the most common example is called furosemide and another drug known as spironolactone is also used quite commonly. When the heart does not work properly fluid can build up in the lungs and elsewhere in the body and diuretics help to get rid of this fluid from the body via the kidneys. Animals on diuretics will therefore urinate frequently and must have access to drinking water at all times.

Other drugs used to treat heart disease include ones that are intended: to try and actually make the heart muscle beat more strongly; to slow the progression of the disease in the heart; or, to make the heart beat with a more normal rhythm. Management of these patients will usually also include some form of exercise control and more recently some diets are also used to try and help support the diseased heart.

Animals that are suffering from a severe flare-up of their heart disease, an acute crisis, will need oxygen therapy and quite intensive care at your veterinary practice and sadly sometimes it is not possible to stabilise them. Cats suffering from blood clot problems can recover to an extent but treatment options are very limited and in the worst cases it is much kinder to put the cat to sleep on welfare grounds. Cats that are less severely affected by a clot will need lifelong treatment for their underlying heart disease and they are usually also started on medication to try and prevent a clot from forming again; aspirin or a drug called clopidogrel are most commonly used for this but you must never administer aspirin or any other drug to your pet without first consulting your vet practice.

Okay so that brings us to the end of this blog on heart disease and heart failure in dogs and cats. There are a number of different types of heart disease and animals can be affected in different ways. The most common scenario is for your pet to be affected long-term, to be on long-term treatment and to slowly get worse, but this is not always the case.  Some animals remain remarkably stable for a very long time while others have a severe crisis from which they do not recover. A number of different treatments may be needed and your vet will talk you through all of this as appropriate.

The next blog will be in approximately 2 to 4 weeks time when we will talk about what can cause a dog or cat to have a red-looking eye. Remember that if you have any comments or questions on this blog, or indeed any suggestions for future blogs, you can contact us in the usual ways. Via email on percypods@gmail.com; via the PercyPods Facebook page; or via Twitter on @PercyPods. Also don’t forget to subscribe for future episodes via the RSS feed. So thank you for reading and until next time, may you and your pets be safe.