Mitral Valve Disease

Mitral Valve Disease (MVD) is the most common form of heart disease in dogs. It generally occurs in small to medium size dogs rather than big dogs. And there seems to be a genetic predisposition to the development of disease as some breeds are more susceptible than others. Those breeds who suffer more than average include: Cavalier King Charles Spaniel, Poodle, Schnauzer, Chihuahua, Fox Terrier and Boston Terrier. MVD has also been seen in the Miniature Pinscher, Whippet, Pekingese, Dachshund, Beagle, Papillon, Great Dane and German Shepherd.  

It is mostly older dogs who tend to suffer from this disease but some dogs are quite young when it begins to occur. 

MVD is a disease affecting the surface of the heart valves. Other names you may hear used to describe MVD are endocardiosis or Valvular Insufficiency. The valves are normally smooth and form a perfect seal when closed. MVD causes the edges to become thickened, lumpy and distorted. The seal is now imperfect and when the ventricle pumps, some of the blood flows backwards into the atrium. This backward flow creates a noise that your veterinary surgeon can hear with a stethoscope. This noise is called a murmur. 

ecause the heart valves are now leaky, circulation is impaired. For a time, your dog’s body may make adjustments to allow it to cope. In fact, some dogs manage with a murmur for many years. However, at some point, the disease overrides the adjustments that have been made and the dog can become unwell and show signs of heart failure. MVD may affect your dog’s body in a number of different ways. 

Signs of heart disease can initially be quite mild and so may be difficult to pick up. However, as the disease progresses, the symptoms can become more severe. These signs occur because of fluid build up or because the vital organs are not supplied with the blood, and therefore the oxygen, they require. Signs include:

The first signal that a dog might have Mitral Valve Disease is the development of a heart murmur. However, a dog with a heart murmur may live a full life span, depending upon the progression of the disease in that particular dog. Some dogs that have developed heart murmurs at young ages have lived to the average lifespan of that breed. A veterinary while listening to a dog’s heart may hear a heart murmur on the left side. (Please note there are other causes for heart murmurs, to diagnose MVD it will depend upon where the regurgitation is heard) The veterinary will then grade the murmur for severity from Grade 1 (mild) to Grade 6 (severe) and depending upon the grade will advise proper treatment. 

Treatment will depend upon the grade of murmur and any clinical signs your dog may be showing. During the early stages of the disease, though a systolic murmur of grade 1-2 is heard there are usually no clinical signs. As the disease progresses, the murmur will become more audible, the dog may become intolerant of exercise, respiratory rate will increase and finally as fluid begins to accumulate in the lungs coughing and laboured breathing develops. Many dogs live for years with a low-grade murmur and treatment consists of dietary changes such as low sodium foods. Some Cavalier King Charles Spaniel breeders are recommending that any dog diagnosed with a heart murmur is put on Co-enzyme Q10. This is a natural medication which may be helpful in treating the disease. While no studies have been done with this medication in dogs, there have been considerable studies in humans and the evidence is pointing to great success in treatment of cardiac disease with its use. Co-enzyme Q10 is an over-the-counter product and can be picked up at virtually any drug store or health food store. As the disease progresses and clinical signs appear such as the coughing and laboured breathing medications such as vasodilators and diuretics will be considered.

At present the mode of inheritance for Mitral Valve Disorder in Cavaliers is unknown. It is considered multi-factorial. In other words, there is a genetic predisposition for the disease but other unknown factors will go into why one dog is affected and at what age and another dog, even a littermate, is not affected at all. While it is extremely doubtful the disease will ever be eradicated from the Cavalier King Charles Spaniel completely, the hope of breeders is to move the age of onset back as late in life as possible. So many breeders will have their dogs checked annually for evidence of a heart murmur and breed mature dogs that are unaffected. By breeding older Cavaliers who are clear of a murmur until as late as possible in life it is hoped that the age of onset will also move back as well.

The Cavalier King Charles Spaniel Club of Canada has recently included the recommendation within its Breeders’ Guidelines that Breeders’ breed Cavalier King Charles Spaniels’ that are at least 2.5 years old and murmur-free that have parents that were murmur-free at age 5 years. Members’ (breeders and pet owners) of The Cavalier King Charles Spaniel Club of Canada have been actively participating in a MVD Heart Study conducted at the University of Guelph, ON since 1992 and still no DNA marker has been determined for the condition. A current research project underway in Europe, LUPA, that is focused on the genetic components of diseases both shared by humans and dogs, including MVD.

Testing is merely a breeder’s tool to try to establish a dog’s health at any point in time. It does not mean that dog may not develop a heart murmur 3 months onwards or that he will not produce puppies with Mitral Valve Disorder. 

Heart testing in Cavaliers is an issue that should not be overlooked for any cavalier owner. All cavaliers should be regularly screened by a cardiologist starting at a year old. While a regular veterinary appointment is ok for general health issues it is not sufficient for heart screening. Only a cardiologist will be able to detect problems in the hearts of our cavaliers before they are at a serious level of Mitral Valve Disease progression. 
There are three ways that a cardiologist will screen your Cavalier for MVD: 

This is the Cardiologist listening to your Cavaliers heart by stethoscope. All veterinarians are trained in auscultation however Cardiologists have special training that allow them a greater understanding of what is heard by stethoscope. A regular veterinarian may miss a grade one murmur, while a cardiologist would be able to hear the slight abnormality through the stethoscope. 

Echocardiogram’s and the use of colour Doppler has allowed Cardiologists the tools needed to obtain very precise information regarding your Cavalier’s heart. On the echocardiogram you are able to clearly see all structures of the heart. The Cardiologist through the colour Doppler is also able to evaluate how the blood is passing through the heart and if there are any abnormalities that are present or may form in the future. For a more detailed look at heart diagnostics please refer to Myra Ehrman’s article that is posted on the Cavalier Club of Canada’s health section of the website. 

The use of radiograph or X-ray’s for screening Mitral Valve Disease is also a useful tool. X-ray’s allow veterinarians to see if the heart has become enlarged or has changed over a period of time. It is a good way to monitor changes in a cavalier who has already been diagnosed with Mitral Valve Disease through an Echocardiogram. It is not a useful way to diagnose if Mitral Valve Disease is present. 

In upcoming months, the Cavalier Club of Canada’s Health & Education Committee will be looking at hosting an annual heart clinic in addition to the study. The purpose of the heart clinic will be to bring in a cardiologist and screen many dogs at one time for Mitral Valve Disease at a reasonable cost. This clinic will be available to breeders and pet owners. More details will be available soon.