Mitral Valve Disease

Degenerative Mitral Valve Disease in Dogs

What is the Mitral Valve?

The mitral valve is a one-way valve between the biggest pumping chamber of the heart (the left ventricle) and the chamber before it (the left atrium). Blood returns from the lungs rich in oxygen. It sits in the left atrium, before passing through the mitral valve into the left ventricle, finally it is pumped into the aorta and around the body.

What is Myxomatous or Degenerative Mitral Valve Disease?

Degenerative changes thicken the mitral valve and it no longer is able to keep blood flow going in a forward direction. The thickened valve leaks blood in the backwards direction and as the disease and leakage progress, the heart enlarges.

Canine myxomatous or degenerative mitral valve disease (MVD) primarily affects older, small to medium size dogs, although any dog can be affected.

Though many dogs are affected in their later years, only about 25 – 50 % of those with MVD experience clinical signs of congestive heart failure (CHF, or fluid build-up within the lungs).

How is MVD diagnosed?

A distinctive heart murmur heard with a stethoscope during the physical exam is the most common early sign of MVD. The murmur is caused by the leaky valve. Once that murmur becomes a grade 3/6 or louder your vet may recommend we investigate further.

Chest X-rays or an echocardiogram (ultrasound of the heart) or both are used to assess the severity of the leak, and the extent of heart enlargement. 

How is MVD treated?

Treatment depends on the severity of the leaky valve and the degree of heart enlargement. Mild leakage with minimal or no heart enlargement is typically monitored at regular intervals without treatment. Dogs with significant heart enlargement benefit from medication, such as pimobendan (Vetmedin), to delay the onset of CHF. Dogs that experience CHF require additional medication, and some dogs need to be hospitalised for heart failure treatment.

What monitoring will my dog need?

Dogs with minimal heart enlargement should be treated as normal dogs, and will just need a check-up every 6 months to listen to their heart murmur.

If your dog has started on medication, they will usually require a check-up 2 weeks after starting treatment, and every 3-6 months thereafter. This may simply be an appointment, or your pet may need repeat ultrasounds, bloods/urine to monitor the kidneys (they work with the heart to maintain blood pressure), an ECG, or even an x-ray to look for fluid in the lungs. Your case vet will explain their recommendations to you.

What can I look out for at home?

The first signs of CHF often include shortness of breath, exercise intolerance, or cough – these signs should prompt a call and usually a vet visit.

In dogs that have experienced an episode of CHF, monitoring the breathing rate during sleep or rest provides a sensitive indicator of how they’re doing - normal is less than 36 breaths/min.

Is diet important?

While some salt restriction (e.g. avoidance of high salt treats) is ideal for most dogs with significant MVD, and moderate salt restriction aids CHF treatment, it’s important that your dog’s appetite remains good, and his or her caloric and protein needs are met. Avoiding non-traditional grain free diets rich in legumes, such as lentils, chickpeas and green peas, is advised.

What is the prognosis with MVD?

Many older dogs affected with MVD will not have their lifespan limited by their heart disease. The rate of disease progression varies, but it most often takes years before clinical signs of CHF develop. After CHF develops, dogs are expected to continue to have an excellent quality of life with treatment, and most survive for an additional 12-18 months, although their survival time varies widely.

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