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What becomes of the broken hearted?

9th February 2017

Probably almost every time you take your pet to the vet, you will see the vet or nurse listen to their chest with a stethoscope. It’s not an excuse not to talk or listen to you – honest! But what are they listening for?

There are three main things the vet is listening to when they are auscultating your pet’s heart. The rate (how fast or slow the heart is beating), the rhythm (is it steady, or an abnormally irregular rhythm?) and the heart sounds – which should be a nice, clear ‘lub-dub’ sound. Abnormalities in the rate could suggest lots of things – a fast heart rate can be due to pain, or fear, for example – but abnormal rhythms or sounds might suggest heart disease.

What should you be worried about if your vet says that they hear a heart murmur, or that your pet is suffering from heart disease? This article discusses the common types of heart disease in dogs or cats, and what we can do about them.

Heart problems in younger pets

Congenital heart disease

Congenital is the name given to a condition that has been present since the animal was born. Luckily, congenital heart problems in dogs and cats are rare, as sadly severely affected animals will often die at or shortly after birth. Sometimes at first puppy or kitten vaccinations a soft heart murmur is heard – this usually indicates abnormal blood flow within the heart, thought to be due to openings between the two sides of the heart that normally close at birth. In most cases, even if this closure is a little delayed, it does still happen without intervention, in which case the murmur disappears.

Heart problems in adult dogs

Mitral valve disease

Mitral valve disease is the most common form of heart disease in adult dogs. It generally presents in middle age, though younger and older dogs can be affected. In certain breeds, such as the Cavalier King Charles Spaniel, it is particularly common. If your vet detects a heart murmur in your adult dog during an examination, chances are that it is because your pet has developed mitral valve disease.

The mitral valve is the name given to one of the valves in the heart (between the atrium and ventricles on the left side of the heart, to be precise). In some dogs, as they age, this valve becomes thickened and irregular. This means it cannot shut properly as the heart beats. Valves within the heart work, just like in any pump, to stop blood going backwards when the heart beats. When the valves do not close properly, most of the blood pumps forwards, but a small amount leaks back through the valves. This leaking creates a ‘whooshing’ sound which can be heard through the stethoscope as the heart beats (instead of the normal ‘lub-dub’ sound).

This leaky valve, just like a mechanical pump, means the heart is not working as efficiently as it should. Mitral valve disease is a particular type of heart disease. However, the body has a collection of mechanisms that help to compensate for this inefficient pumping. It is only when these mechanisms have been overwhelmed that the animal starts to show clinical signs of disease – this means they are now suffering from congestive heart failure (CHF), secondary to mitral valve disease.

Previously, treatment of heart disease was not recommended before dogs started to show signs of heart failure. Signs of CHF developing might include an increased respiratory rate at rest, a cough (particularly when lying down), decreased energy levels or exercise tolerance, or fainting spells in more severely affected dogs. If your dog has been diagnosed with a heart murmur, the vet will recommend that you monitor them very closely for these signs.

Last year, the results of a long running study into a medication (Vetmedin) used to treat heart failure were published (the EPIC study). This study particularly looked at treating dogs before the onset of heart failure, to see if it could be delayed. The study found that treating dogs which had mitral valve disease, and an enlarged heart as a result, with Vetmedin delayed the onset of heart failure and the need to start other medications. If a murmur is detected in your dog, the size of their heart can be measured using an x-ray or an ultrasound scan of the heart (echocardiography). These tests can be performed here at Orchard Vets, or your pet can be referred to a specialist in cardiology for a more detailed examination.

In dogs that are showing signs of congestive heart failure, medications can be given to alleviate their signs and improve their quality of life and life expectancy. But what are they, and how do they work?

Pimobendan (Vetmedin): Vetmedin is indicated to be used in dogs that are suffering from mitral valve disease, and also congestive heart failure due to mitral valve disease. It helps the heart to beat more strongly, and also slightly dilates blood vessels in the body, reducing the pressure against which the heart has to beat, making its job slightly easier.

ACE inhibitors: or angiotensin-converting-enzyme inhibitors such as Benazecare act to relax blood vessels in the body, lowering blood pressure and decreasing the work the heart has to do every time it beats, and therefore reducing its oxygen and energy demand.

Diuretic: increased blood pressure in the circulation supplying the lungs, due to the inefficient pumping of the heart, can cause fluid to accumulate in the tiny air spaces of the lungs (the alveoli). This reduces the body’s ability to absorb oxygen, and results in a cough as the dog attempts to clear fluid from their airways. Diuretics increase the loss of fluid from the body through the kidneys, helping to clear fluid from the lungs. The most commonly used diuretic is frusemide, though some patients will need a drug called spironolactone instead, or in addition. The action of the drug means that pets need to drink more and go to the toilet more often when taking these medications.

Dilated cardiomyopathy

Dilated cardiomyopathy is a type of heart disease primarily seen in larger breed dogs, particularly Doberman Pinschers. Unlike mitral valve disease, this does not present with an audible murmur, so is more difficult to detect before dogs become unwell.

In dilated cardiomyopathy, the muscles of the wall of the heart become weaker. Because of this, the heart wall becomes thin and stretched, and is not able to beat as efficiently. This results in similar outcomes as in mitral valve disease.

Dogs that are entering congestive heart failure due to dilated cardiomyopathy may be less able to exercise, or have collapsing or fainting episodes. More commonly noted would be a productive or moist cough that does not go away. In some cases the stretch on the heart damages the cells that conduct the electrical signals controlling the heartbeat, leading to an irregular rhythm.

Dilated cardiomyopathy is diagnosed by using a ultrasound scan of the heart to measure the size of the chambers and the thickness of the walls. There is also a blood test available (the proBNP test) to measure stretch on the heart that can be useful in screening for, or monitoring, heart disease.

Congestive heart failure due to dilated cardiomyopathy is generally managed in the same way as congestive heart failure due to mitral valve disease.

Heart problems in adult cats

Heart problems in cats are less common than in dogs, but unfortunately are often much more serious. Part of the problem is that cats are particularly good at hiding signs that they are unwell, so by the time heart disease is evident, they are often in a critical condition. Sometimes the first signs of heart disease that is evident in cats is marked difficulty in breathing, or paralysis of the hind legs.

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is much more common in cats than it is in dogs. Some breeds, such as the Maine Coon and Ragdoll are predisposed and a genetic test is available for these animals before breeding to try to reduce the incidence of this devastating illness within the breed.

In hypertrophic cardiomyopathy, the walls of the ventricles, the main pumping chambers of the heart, become abnormally thickened. This means that it is difficult for blood to enter the heart, as the heart is not able to stretch. The other chambers of the heart, the atria, become stretched and damaged due to the extra work trying to push blood in to the ventricles.

Increase in the blood pressure in vessels around the lungs leads to fluid leaking from the vessels, just like in dogs. In cats, rather than leaking in to the air spaces, this leaks into the space between the chest wall and the lungs. This fluid compresses the lungs and makes it very difficult for the cat to breathe. This causes the cat to breathe rapidly, taking small shallow breaths. They may breathe through an open mouth. A cat that is breathing through an open mouth is very unwell (though heart problems are not the only cause) and needs emergency treatment. They should be handled very gently as any stress can make them significantly worse.

Inside the heart of a cat with heart disease, blood often does not move very well. This means it can start to form a solid clot within the atria of the heart. Pieces of this clot can then break off and travel through the heart and large blood vessels (called a thrombo-embolism). The first place that these vessels significantly narrow is where it branches to supply the back legs, so this is usually where the clot will lodge. This blocks off blood supply to the legs, causing paralysis. Cats with this condition (known as a femoral arterial thrombo-embolism ‘FATE’ or saddle thrombus) are usually unable to rise on their back legs, and their paws are often very cold. In many cases, they will be crying out, as the condition is very painful. Sadly, in nearly all cases it is not possible to re-establish blood supply to the back legs and the damage to the tissues is in any case catastrophic and irreversible. In this situation, the kindest decision for the cat is euthanasia.

This information isn’t designed to frighten you, but hopefully to reassure. Nor is it designed to replace advice from your pet’s veterinarian As ever, if your vet has any concerns about your pet’s health during a consultation they will alert you and discuss their recommendations. Equally, if you have any concerns about your pet’s well-being, whether you think you know what it might be or not, contact us at the clinic to arrange an appointment.

Dr. Lucy Fleming MRCVS