For this next blog on congenital cardiac conditions, we’ll focus on mitral valve dysplasia and ventricular septal defects.

Mitral valve dysplasia is not common in cats or dogs, but when it is seen, it is more likely to be seen in large breed dogs. The mitral valve is located in the left side of the heart, where it separates the two chambers of the left heart. In mitral valve dysplasia, the mitral valve is malformed and is unable to form a sufficient seal when closed. This allows blood to flow (or regurgitate) from the left ventricle into the left atrium, also known as mitral regurgitation.

Mitral regurgitation causes the heart to have to work harder, and like any muscle, when it works hard, it gets bigger. Enlarged heart muscles pump inefficiently and lose flexibility, resulting in decreased filling ability and poor function. Over time, mitral valve dysplasia will lead to congestive heart failure.

Mitral valve dysplasia is managed medically. At this time, mitral valve replacement is simply not feasible in pets.

Fortunately, mitral valve dysplasia is rare. Breeds that are overrepresented are:

  • Bull terriers
  • Dalmatians
  • German Shepherds
  • Golden Retrievers
  • Great Danes
  • Mastiffs, and
  • Newfoundlands

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Ventricular septal defects occur when the heart is being formed and are a result of the failure to close of the wall between the ventricles of the left and right heart. Simply put, a ventricular septal defect is a hole in the heart, allowing communication between the left and right heart. Most of these defects cause left to right shunting, similar to that seen in patients with a patent ductus arteriosis. The left heart is stronger than the right heart, so blood naturally flows through the defect from left to right when the heart contracts. For this reason, blood meant for the tissues of the body gets redirected to the lungs.

As is the case in any heart condition, when blood flow is disrupted, the heart has to work harder and eventually will start to fail. In the case of ventricular septal defects that shunt from left to right, the left heart will start to fail, leading to congestive heart failure.

When ventricular septal defects are very large, the two ventricles start to function as one, mixing blood from both the right and the left sides. This leads to enlargement (and eventual failure) of both sides of the heart.

Luckily, most ventricular septal defects are small, and in these cases, there are generally no signs of disease. Your veterinarian may hear a murmur and refer your pet for an echocardiogram, but chances are that your pet will lead a full, healthy life.

For more severe cases, congestive heart failure is managed medically. Surgical repair of the defect is rarely performed.

Stay tuned for our final blog on congenital heart defects, where we will examine a condition called Tetralogy of Fallot.

Feb 20, 2013
Pet Health

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