Heart disease in dogs – mitral valve disease

The most common form of heart disease in dogs is Mitral Valve Disease.  It can occur in any dog, but is most common in small or medium sized breeds.  One of the most common breeds we see the disease in at Greenbay Vets is the Cavalier King Charles Spaniel – unfortunately the disease is very common in this breed, and these lovely little dogs are also popular pets in Torbay.

About Mitral Valve Disease (MVD)
MVD affects the heart valves between the chambers in the left side of the heart (the mitral valves).  In a normal heart blood should flow in to the left side from the lungs into a chamber called the left atrium.  The blood then moves into the pumping chamber, the left ventricle, from where it is pumped into the main blood vessel, the aorta, and around the body.

Normal heart

When the ventricle pumps, the mitral valves should close so that blood is forced into the aorta and cannot leak back into the atrium.  Unfortunately in dogs with MVD the valve is diseased and becomes leaky.  Some blood therefore leaks back into the atrium, rather than being pumped around the body.  The vet can hear this leak as an abnormal heart sound, or murmur, when listening with a stethoscope.  The louder the murmur, the more blood is leaking the wrong way.

Heart with mitral valve disease

How do I recognise MVD in my dog?

In the early stages of the disease you will not see any change in your dog.  A vet will be able to hear a heart murmur, but the heart is coping with the level of leakage, and your dog will manage as normal.  There are other causes of a heart murmur, although MVD is the most common cause in a small/medium sized dog who has acquired the murmur as an adult.  To be sure of the cause, an ultrasound of the heart needs to be performed. An ultrasound is a non-invasive procedure, which is usually done without any sedation on a day patient basis.

Over time, as the disease progresses, your dog’s heart will start to struggle.  Initially the left atrium will get bigger, due to the amount of blood leaking back into it.  This can be seen by a vet using an ultrasound scan of the heart and can cause your dog to cough as it presses on the windpipe.

Eventually, the heart is unable to pump enough blood around the body and the dog goes into heart failure.  This results in signs such as reduced exercise tolerance and feinting due to lack of blood getting to the brain and muscles.  It also causes difficulty breathing, due to fluid building up in the lungs.  Initially this causes an increase in breathing rate, and eventually pronounced difficulty breathing.  In some cases fluid can also build up in the tummy.  Heart failure is diagnosed by the vet using a combination of signs and tests such as x-rays, ultrasound and blood tests.  There are other diseases that can cause similar signs.

If the vet diagnoses a heart murmur in your dog, it is recommended to closely monitor:

• their ability to exercise e.g. how long it takes them to do their normal walk
• their breathing rate (how many breaths they take in a minute while resting) – there is a useful app for this (search for Cardalis app)
• for the development of a cough

You can view a useful video about MVD here.

The importance of regular check-ups

As the early stages of the disease do not cause any symptoms, it is recommended that all dogs have a yearly check up with the vet, who will be able to detect a heart murmur using their stethoscope.  This is done at the annual health check performed at the same time as any booster vaccinations.

If a murmur is detected, you may be offered an ultrasound scan to confirm the cause and the severity of the disease.  As a minimum you should be advised on how to monitor your dog, as above, and you may be advised to come in for a check up every 6 months.  The vet will be checking to hear if the murmur is getting louder, as well as for any changes in heart rate and rhythm, and will ask questions about how your dog is getting along.  Unfortunately MVD is a progressive disease, but many dogs will live for several years with a murmur before the disease causes them a problem.

Treatment

Until recently, there was no evidence to treat a dog with MVD unless they were in heart failure.  Unfortunately there is no cure for the disease, but the symptoms can be managed with various drugs for a period of time.

The drugs most commonly used include:

• A diuretic e.g. furosemide. This is used to increase the removal of fluid from the body.
• Pimobendan. This increases the contractility of the heart and reduces the resistance against which the heart must work.
• An ACE inhibitor e.g. benazepril.
• Spironolactone.

The latest evidence has shown there is a benefit to treating dogs with the drug pimobendan when they show evidence of heart chamber enlargement, before they are showing signs of heart failure.  This chamber enlargement can be diagnosed by a vet using an ultrasound scan (or an x-ray).  You can read more about this latest study here.

There is much more to the ‘annual visit’ than a vaccination booster injection, checking the heart is just one of the many checks the vet will do during the appointment.  If your dog hasn’t been checked by a vet within the past 12 months we strongly recommend a check up.

Dr Laura Mather, Vet at Greenbay Vets in Torquay and Paignton