What is it?
Valve Disease, also known as Endocardiosis or Valve Incompetence, is the most common heart disease in dogs - over 30% of dogs will develop some degree of valve disease by 12 years of age. As a result, it is the most likely diagnosis (although not the only one) in an older dog with a heart murmur.
What causes it?
Inside the heart there are four valves, which work to make sure that blood only flows one-way through the chambers. These are the left atrioventricular (the Mitral or Bicuspid Valve); the right atrioventricular (the Tricuspid Valve); the Aortic Valve and the Pulmonic Valve. Over time, in some dogs, these will start to degenerate, with nodules or bits of scar tissue forming on the edges. This prevents the valve from closing properly, leading to "regurgitation", or leakage of blood. Over time, this reduces the heart's efficiency, leading to heart failure. Although any valve can be affected, the Mitral Valve is the most commonly involved, in roughly 95% of cases.
What dogs are at risk?
Any older dog may develop valve disease; however, some breeds of dog are at increased risk. The highest risk is seen in Cavalier King Charles Spaniels, closely followed by Chihuahuas, Cocker Spaniels and a number of other small and toy breeds. Male dogs are at slightly higher risk than females; and the commonest age of onset of heart failure is 10-12 years (although the heart murmur is often detected 2-3 years before that). Cavalier King Charles Spaniels are unusual in that not only is the condition very common, but it develops rapidly, with most affected dogs developing signs of heart failure by 8 years old.
What are the symptoms?
Initially, the only symptom is a heart murmur - an abnormal noise caused by the blood rushing in an unusual direction which the vet will hear when they listen to the dog's chest. As the disease progresses, signs of heart failure will, sooner or later, develop, with reduced exercise tolerance, coughing, panting or difficulty catching breath. Eventually, the heart will fail, leading to profound weakness, pale gums, difficulty breathing, swelling of the abdomen, collapse and (eventually) internal drowning from fluid in the lungs.
How is it diagnosed?
In a high risk breed, hearing a murmur is highly suspicious, and may be sufficient to start treatment. However, to confirm the diagnosis, chest X-rays (to demonstrate an enlarged heart) and ultrasound (echocardiography) are required.
How can it be treated or managed?
The condition cannot yet be cured (although there is experimental heart surgery being tested at the RVC in London). However, there are a wide range of medications available to manage the condition. The most commonly used are diuretics ("water tablets" like frusemide or spironolactone, which prevent fluid build up), ACE Inhibitors (such as benazepril, which improve the dog's quality of life and how well they feel), and drugs to increase the strength of each heartbeat (Pimobendan, which increases lifespan).
Can it be prevented?
No - however, recent research (the EPIC trial) suggests that starting a dog on Pimobendan before they develop symptoms significantly delays the onset of heart failure.