What is mitral valve disease and can it be cured?
The most common heart condition in dogs is called endocardiosis - and the most common form of endocardiosis is MVD. So, what is it, how is it diagnosed, and what can be done about it?
What is endocardiosis?
Put simply, it’s degeneration of the valves in the heart - which is why it’s also called valve disease. Inside the heart there are four valves (mitral, tricuspid, aortic and pulmonic), and endocardiosis can (and does) affect any or all of these. That said, the mitral valve is most commonly involved. Some breeds are predisposed - for example, Cavalier King Charles Spaniels are at very high risk of MVD.
Why is this important?
The valves work to maintain a one-way flow of blood through the heart. In endocardiosis, the edges of these one-way valves become thickened and irregular, so they become leaky (this is known as valve incompetence or valve leakage). This means that blood leaks backwards through the heart, reducing heart efficiency.
Now, for a while, the heart can compensate for reduced efficiency by increasing the strength of each beat, and the heart rate. This is known as the compensation phase, and usually the only symptom is a heart murmur (an abnormal sound heard when listening to the heart with a stethoscope, caused by irregular bloodflow).
However, the compensation phase won’t last forever, and eventually the heart will begin to fail. Initially, this presents with a reduction in the dog’s ability to exercise, but it will progress to congestive heart failure.
What is congestive heart failure?
CHF occurs when the heart’s pumping capacity begins to fail. There are two components - pump failure and excessive water retention. These two go hand in hand, as reduction in pumping capacity causes a reduction in blood pressure, which triggers a number of body systems that work to retain water and salt, boosting blood pressure. This system is great if the dog has lost blood pressure because of bleeding, but in heart failure, it actually makes things worse because the heart now has to work even harder to shift the extra blood volume around the body. This results in heart enlargement (mainly of the left atrium), which further reduces the heart’s efficiency and pumping power.
CHF causes a range of symptoms, but these usually include:
- Difficulty exercising and blueness of the gums, because the heart can’t get enough oxygen to the muscles.
- Coughing, as the enlarged heart presses on the airway.
- Fluid in the abdomen (ascites) and lungs (pulmonary oedema), as fluid “backs up” behind the heart, filling the lungs and organs with fluid.
- This is usually the cause of death - the dog drowns in the excess fluid in their lungs.
How is it diagnosed?
Often, we will be able to make a pretty good guess as to what the problem is just by listening to your dog’s heart, to hear what sort of murmur they have, and where in the heart it seems to be coming from. However, we will often also do X-rays to assess how large the heart is and how much fluid there is in the lungs. However, the “gold standard” technique is for us to use echocardiography to look inside the heart using ultrasound, and see exactly what’s going on.
What treatment options are there?
At the moment, MVD and other forms of endocardiosis are not considered curable (but see below!). However, congestive heart failure can be managed effectively with drugs, often for years. The main drugs used are:
●Diuretics, such as frusemide or spironolactone. These reduce the amount of water in the body, helping to keep the lungs dry so the dog can breathe.
●ACE inhibitors, a class of drugs that reduce the abnormal fluid buildup. These don’t improve lifespan, but massively improve your dog’s quality of life.
●Pimobendan, a drug that helps the heart beat harder, prolonging life.
There are management changes as well which are also useful - exercising little and often, keeping your dog cool, and monitoring their sleeping respiratory rate (an increase is often the earliest sign that fluid is starting to build up in the lungs). In addition, special cardiac diets exist that are also helpful.
What about surgery?
There is one experimental procedure being researched at the moment by vets at the Royal Veterinary College in London, and following the work of a team in Japan. This involves surgically replacing the damaged valves. At the moment it isn’t widely available, but the initial results look very promising!