Getting to the Heart of the Matter: Mitral Valve Disease
Having a pet diagnosed with heart disease can be a confusing and overwhelming experience. Maybe your veterinarian mentioned that your dog has a heart murmur, and you are not sure how concerned you should be.
Or your dog suddenly developed difficulty breathing, was hospitalized, and now you are dealing with a new, life-threatening diagnosis for your beloved pet. Either way, understanding what is happening and how it is being treated can make the process much more manageable.
What is the heart’s job in a healthy animal?
The heart acts as a pump to push blood through the body, in order to deliver oxygen. It is divided into two sides, right and left, each of which has two chambers. The top chamber of each side is called the atrium. It is divided from the bottom chamber, the ventricle, by a valve. Oxygenated blood from the lungs flows into the left atrium, then goes to the left ventricle. The left ventricle squeezes with each heartbeat to pump blood out to the body. Once the body has used up the oxygen in that blood, the deoxygenated blood flows back into the right atrium, then into the right ventricle. Then the right ventricle pumps blood back to the lungs to reload it with oxygen.
What goes wrong with valve disease?
This natural process is disturbed with valvular disease. In mitral valve disease specifically, the valve inside the left side of the heart begins to degenerate and become abnormally shaped. When this occurs, blood can leak around it and flow backwards. Mitral valve disease is the most common type of heart disease in dogs, especially small and medium sized dogs. It typically develops in middle age, and becomes more serious as dogs age.
When mitral valve disease is present, a portion of the blood that should go forwards from the ventricle, out to the body, leaks backwards into the left atrium. With less blood going out to the body, blood pressure drops. The body attempts to adapt to this abnormal blood flow. Regulatory mechanisms act to retain salt and constrict blood vessels to maintain blood pressure.
The heart also remodels itself. The left atrium gets bigger to accommodate the extra blood. The left ventricle also enlarges, in order to try to get more blood out to the body.
Eventually, this remodeling can become maladaptive. The leaky valve can actually become leakier as the heart enlarges around it. The enlarged heart can also become more susceptible to arrhythmias (abnormal rhythms). In end stage heart disease, the enlarged atrium can no longer accommodate the backwards flow of blood. Blood then backs up into the vessels in the lungs, and leaks out into the lungs, a condition called pulmonary edema. This process is known as left sided congestive heart failure.
What signs may you see if your dog has mitral valve disease?
For many dogs, their disease will never progress to congestive heart failure.
These pets, and those early in the disease, may not have any signs noticeable at home.
Your veterinarian may hear a heart murmur on physical exam, which is caused by the turbulent flow of blood going backwards into the atrium. For dogs that develop congestive heart failure, more serious signs will be present. These can vary from dog to dog, but the most common are difficulty breathing and coughing. The coughing may be worse at night, or with exercise. There are many other causes of coughing in older small breed dogs, so it is important for a veterinarian to specifically diagnose heart disease in your pet. Other dogs may develop weakness, lethargy, or weight loss. A few many have syncopal episodes (fainting). In some dogs, signs can develop insidiously over several weeks.
In others, heart failure may develop almost overnight. The onset can be triggered by a stressful event, such as overheating or significant exertion.
One fairly sensitive indicator of congestive heart failure in dogs with heart disease is an increase in sleeping respiratory rate. To calculate this, count how many breaths your dog takes per minute when he or she is completely asleep. One rise and fall of the chest is one breath. This rate should be less than about thirty-five breaths per minute. If your pet has previously been diagnosed with heart disease, and their sleeping respiratory rate is repeatedly higher than this, you should seek veterinary care.
What tests are used to diagnosis mitral valve disease?
If your veterinarian is concerned about the presence of mitral valve disease in your dog, he or she may suggest several different tests. The most common test is chest radiographs (x-rays).
In asymptomatic dogs with a murmur, this can be used to check for heart enlargement, a sign of more advanced disease. Chest radiographs are also critical for diagnosing congestive heart failure, as they allow visualization of fluid in the lungs. Your vet may also suggest screening bloodwork to rule out other diseases, or to ascertain if it is safe to start certain medications. In many cases, he or she may suggest referral to a cardiologist or radiologist for an echocardiogram.
This is an ultrasound of the heart, and is used to visualize the interior of the heart itself, as well as the valves themselves. This allows a specific diagnosis of the type of heart disease present, and facilitates the most targeted treatment recommendations. If there is a concern for arrhythmias, an electrocardiogram (ECG) may also be performed.
This allows assessment of the heart’s rhythm, and may be done as a brief in office test, or a longer period of time with a wearable monitor.
Once mitral valve disease is diagnosed, what does treatment look like?
Dogs that have not yet developed congestive heart failure may not require any medications. Dietary adjustments, including salt restriction, may be helpful. One medication, pimobendan, has been shown to delay time of onset to congestive heart failure in dogs with mitral valve disease. This medication acts to help the heart beat more strongly, and may be suggested if your pet has signs of heart enlargement on radiographs. Once congestive heart failure has developed, diuretics are the mainstay of treatment. These act to reduce the amount of fluid in the body, in order to decrease or eliminate pulmonary edema. If severe congestive heart failure has developed, your pet may require hospitalization on oxygen and injectable diuretics. When they are more stable, they will likely go home on an oral version of the diuretic called furosemide. In some cases, additional medications to decrease blood pressure or reduce cardiac remodeling may be prescribed. While the underlying disease cannot be cured, medications can decrease symptoms and slow disease progression.
What is the prognosis for dogs with mitral valve disease?
This depends on several factors, including how advanced the disease is. Dogs that are asymptomatic may never go on to develop heart failure, and may have a completely normal life expectancy. Once congestive heart failure develops, about fifty percent of treated dogs will survive one year, and about twenty five percent to two years. But each pet is different, and some may be able to be managed for several years. Unfortunately, as valvular disease is typically progressive, medications will eventually become insufficient to control signs.
However, in between episodes of congestive heart failure, many dogs with advanced mitral valve disease live happy lives, with a good quality of life. If you are concerned about your pet’s heart disease,
be sure to talk to your veterinarian about the best treatment recommendations for him or her.
Brister, J, Lake-Bakaar, G, and Rishniw, M. (2018). Heart Failure, Left-Sided Retrieved November 1, 2018, from https://www.vin.com.
Rishniw, M. (2005). Myxomatous Mitral Valve Degeneration. Retrieved November 1, 2018, from https://www.vin.com.
Rush, J. (2016). Acquired Cardiovascular Disease in Dogs. In Southwest Veterinary Symposium. Retrieved November 1, 2018, from https://www.vin.com