Chronic Valve Disease

How does the heart work?

The heart has four chambers. The upper chambers are called atria (singular: atrium) and the lower chambers are called ventricles. The heart is also divided into right and left sides.

The right side of the heart pumps deoxygenated blood returning from the venous system in the body into the lungs.  From the lungs, oxygenated blood enters the left side of the heart where it is pumped out into the tissues of the body through the arteries. 

The valve that separates the left atrium from the left ventricle is called the mitral valve. The left ventricle is surrounded by the largest and strongest of the heart muscles. This large muscle is necessary to pump blood throughout the body.

What is chronic valve disease?

Chronic/Degenerative valve disease (CVD), refers to a noninfectious degeneration of the cardiac valves.  In dogs and cats, the most commonly affected valve is the mitral valve, followed by the tricuspid valve.  The pulmonic and aortic valves are rarely affected by this condition.  For reasons we don’t completely understand, in some breeds the mitral or tricuspid valve leaflets can become abnormally thickened and develop a nodular appearance.  These, and other changes to the valves, impede their ability to form a tight seal between the atrium and ventricle during contraction of the heart muscle therefore they begin to leak.  As a result, some of the blood in the ventricle now flows back into the atrium through the leaky valve (known as regurgitation) instead of moving forward from the ventricle into the aorta (on the left side) or pulmonary artery (on the right side) with each beat.  

How common is chronic valve disease?

Chronic valve disease is the most common cardiac disease in dogs. This is more common in small breed dogs, such as Miniature Poodles, Cocker Spaniels, Miniature Schnauzers and Dachshunds. Cavalier King Charles Spaniels are also commonly affected and tend to develop the disease earlier and progress faster than the other breeds.  

What are the consequences of a leaking mitral/tricuspid valve?

The earliest sign of a leaking mitral valve is a heart murmur. This is produced by the turbulence created when some of the blood goes backward through the leaking valve into the left atrium. Many dogs develop a murmur from the mitral valve as early as six years of age. This problem is especially common in small breeds of dogs. A heart murmur does not mean that heart failure is imminent. But as time goes on, the leak can become more severe and more and more blood flows backwards. This results in reduced pumping efficiency and, in severe cases, congestive heart failure. 

What is congestive heart failure?

Congestive Heart Failure (CHF) is a term that refers to the heart’s inability to pump adequate blood to the body. There are many causes of CHF in dogs. The two most common causes are mitral valve insufficiency (MVI) and dilated cardiomyopathy (DCM).

Clinical signs vary depending on whether the dog has left- or right-sided heart failure. The most common symptoms are decreased stamina, coughing or difficulty breathing.

Is CHF due mainly to heart valve disease?

CHF is most commonly caused by valvular insufficiency. It is estimated that 80% of the canine CHF cases are caused by MVI. However, there are many other causes. Disease of the heart muscle (cardiomyopathy), irregularities of rhythm and narrowing of some of the major blood vessels can also cause CHF.

What clinical signs should I expect?

CHF usually results in coughing, ascites (fluid in the abdomen), exercise intolerance, general lethargy, weakness and weight loss despite having an enlarged abdomen due to ascites. The normal pink color of the mucous membranes may become pale or bluish color.