Mitral valve disease and tricuspid valve dysplasia

Heart valve dysplasia can affect the aortic, pulmonary, mitral or tricuspid valves of the heart. The most common one to affect dogs is mitral valve disease and the RVC is one of a few centres in world to correct the condition with surgery.

The open-heart surgeries performed most frequently at the RVC are valve repair in dogs with either mitral valve disease or tricuspid valve dysplasia. The RVC has substantial expertise in both researching and treating these and other cardiovascular diseases. Lower down this page is information on other canine diseases that can also be treated with open-heart surgery.

Mitral valve disease and repair

The mitral valve acts as a seal on the left side of the heart, between the atrial chamber (the filling chamber) and the ventricle (the pumping chamber). When the ventricle contracts, oxygenated blood is pumped around the body, the mitral valve serves to ensure ‘forward flow’ and prevents any blood from being pumped back into the filling chamber.

Mitral valve disease is a degenerative condition that over time causes the valve edges to become thickened and knobbly. This allows blood to leak back into the atrium. The chords that control the movement of the valve leaflets ensure a good seal. Elongated or ruptured cords allow even more blood to regurgitate back into the atrium.

As the atrium gets bigger from the additional volume of blood, the valve edges are pulled further apart. This creates more leakage of blood, exacerbating the condition. As there is then increased pressure in the left atrium, blood returning from the lungs into the atrium gets ‘backed up’, which leads to fluid leaking into the lungs (pulmonary oedema) and this signifies heart failure.

The aim of surgery is to reduce the volume of blood leaking back through the valve, which will also enable the heart to remodel, and allow the left atrium to shrink back towards normal size. To achieve this, a valve repair is performed. This consists of replacing any ruptured or stretched chords with artificial chords made from Gore-Tex.

Experience with repair of the mitral valve has shown that dramatic results are obtained when the valve is made more competent. Even dogs in end stage heart failure can recover relatively normal cardiac function and no longer require diuretic therapy. The estimated chance of dogs surviving surgery is around 70%.

As repair is unlikely to make the valve ‘perfect’, some valve leakage would be expected post-treatment. However, in most instances this is a much smaller leak than the dog had previously.

To read more about mitral valve disease and treatments, including medical management, click here. 

Tricuspid valve dysplasia

Tricuspid valve dysplasia is an unusual congenital (present from birth) condition in dogs. In affected dogs,  the valve has not formed properly. This malformation enables the backflow of blood from the right ventricle of the heart to the right atrium.

Over time the leak is likely to get worse, the backflow increases and the right atrium and ventricle become enlarged. The increasing pressure in the cardiovascular system can result in fluid building up in the abdomen (which is known as ascites) and around the lungs (pleural effusion). This stage of disease is known as congestive heart failure.

Owners might notice their dog having a reduced ability to exercise, laboured breathing and/or a swollen abdomen. Some will collapse after exerting themselves. However, in some cases, no signs of disease will be apparent to owners and the disease is identified during a routine veterinary checkup.

Medication can be used to reduce fluid build-up and to support the functioning of the heart but in some dogs surgery is required to enable them to live a longer and more active life. In 2016, the RVC became the first veterinary service in the world to successfully treat a dog's stenotic (narrowed) tricuspid valve with open-heart surgery.

Congenital heart defects

Open-heart surgery can be considered for a variety of congenital heart defects in dogs including atrial septal defect, ventricular septal defect, pulmonic stenosis, double-chambered right ventricle, tetralogy of Fallot and some patients with subaortic stenosis.

The general indication for open-heart correction of congenital heart defects is that they are hemodynamically significant (determined by medical cardiologist based on cardiac evaluation). In general, open-heart correction of congenital septal defects is undertaken with curative intent. Dogs should be at least five months old before undergoing open-heart surgery and be free of other life-shortening congenital defects.