Update on Mitral Valve Disease Research

Mitral valve disease (MVD) is a condition where, over time, the mitral valve of the heart degrades. The heart is separated into 4 chambers; top and bottom, left and right. The upper chambers are the atria (singular atrium) and the lower chambers are the ventricles. There are valves which are in place between each of the chambers to keep blood flowing in one direction. Blood travels from the right atrium to the right ventricle into the lungs, where it is oxygenated, then into the left atrium and finally to the left ventricle and out to the rest of the body. The mitral valve is located between the left atrium and the left ventricle. It functions here to prevent the back flow of blood back into the left atrium. When functioning correctly all the blood contained in the left ventricle will be pumped out into the body as the heart contracts. As the mitral valve degrades it cannot close properly and small amounts of blood leak back into the left atrium. The condition is progressive and over time the valve will continue to degrade until the heart can no longer compensate. The result of this is that the heart must work harder to supply blood to the body. This eventually leads to congestive heart failure. Mitral valve disease is seen most often in older, small dogs.

The exact cause of MVD is not known. In some breeds, however, there is very strong evidence that it may be genetic. Learn more about mitral valve disease.

Dr. Mark Oyama, DVM, is a professor at the University of Pennsylvania School of Veterinary Medicine. Dr. Oyama has had seven different research grants funded by the AKC Canine Health Foundation (CHF). In his research Dr. Oyama is looking at the causes – genetic and otherwise -- of MVD as well as treatments that can provide a better quality of life.

CHF recently had an opportunity to interview Dr. Oyama about his MVD research.

CHF: Tell us a bit about MVD. How is it diagnosed? What are some common signs and symptoms that pet owners should look for? What is the current treatment for MVD?

MO: Degenerative mitral valve disease is a disease that develops as dogs age.  The disease is caused by degeneration and changes within the mitral valve leaflet which result in leaks through the valve and the development of a heart murmur.  In most dogs, the disease will not progress to the point of ever producing symptoms, however, in dogs with severe mitral valve disease congestive heart failure can develop.  Typical signs of congestive heart failure include increased respiratory effort and breathing rate, activity or exercise intolerance, general lethargy, poor appetite, and fainting.  If dogs experienced heart failure due to mitral valve disease, typical therapy includes diuretics to alleviate abnormal fluid buildup in the lungs (pulmonary edema), Ace inhibitors, and a drug to improve the strength of the heart muscle.

CHF: Are there specific breeds that are predisposed to MVD? Is there an age when MVD is typically diagnosed?

MO: Small breed dogs are predisposed to mitral valve disease.  Some breeds of dogs have a very high incidence of disease such as Cavalier King Charles Spaniel.  Other common breeds that develop mitral valve disease include Toy Poodles, Cocker Spaniels, Pomeranians, and Yorkshire Terriers.  Mitral valve disease becomes more common as dogs age.  Most dogs with mitral valve disease first develop a murmur between the ages of 6 and 10.

CHF: Tell us about the CHF-funded research you are currently working on for MVD.

MO: The research we are involved in includes evaluation of new drugs for mitral valve disease including new diuretics.  We are also participating in a worldwide clinical trial to evaluate the ability of heart muscle drugs to slow progression of disease and prevent the development of congestive heart failure.  We are also interested in the molecular pathways that lead to the development and progression of mitral valve disease.  In particular we and other groups have been investigating how the serotonin pathway could potentially be involved in mitral valve disease.

CHF: What are the results of your research?

MO: Our research is in the very early stages.  Thus far we have high hopes that a new diuretic offers distinct advantages over furosemide, which is the most commonly prescribed diuretic in dogs with heart failure.  We are working to establish the efficacy and safety of this diuretic in preparation of planning clinical trials to evaluate its effects as compared to furosemide.  The potential role of serotonin in mitral valve disease is still unknown, but early studies are very intriguing, and indicate that dogs with early mitral valve disease have elevated blood serotonin levels.

CHF: How might your research help with the overall health and comfort of dogs affected with MVD? Might your research lead to better pain management and/ or a better quality of life?

MO: Our research is centered on helping dogs with congestive heart failure have improved quality-of-life and reducing risk for continuing signs of congestive heart failure.  Our research involving serotonin and other pathways involved in the development and progression of disease are ultimately targeted towards discovering the underlying abnormalities that produce mitral valve disease in dogs.  If serotonin and other pathways contribute to disease formation blockade of these pathways could result in reduction in disease development and progression.

CHF: What role might early detection play in adequately treating MVD? Can wellness visits assist in early detection?

MO: The earliest sign that dog has developed mitral valve disease is a development of a heart murmur.  The murmur is easily detected by listening to the heart with a stethoscope.  Many murmurs are detected during the dog’s annual wellness exams with her family veterinarian.  Detection of a heart murmur is often followed up by performing chest x-rays which help determine the size of the heart and severity of the heart leak.  Other diagnostic tests can include cardiac ultrasound or echocardiography.  Depending on the severity of disease and progression of disease as measured by radiograph or echocardiograph, heart size therapy may or may not be indicated.  Again it's important to remember that most dogs with mitral valve disease and a heart murmur will never develop enough disease to produce congestive heart failure, and the objective of the veterinarian is to identify those dogs that have rapidly progressive disease and will be at risk for heart failure in the future.