Tricupsid Valvular Dysplasia and Congestive Heart Failure

The following article was composed by Rachel Peeples.

In the mammalian heart there are two sides, a left and and a right, and each side has two chambers, the atrium and
the ventricle.  The right atrium takes returning blood from the veins of the body that is low in oxygen.  This blood then flows into the right ventricle which contracts and sends the blood to the lungs to get oxygen.  The blood leaves the lungs and goes to the left atrium which then sends the blood to the left ventricle.  The left ventricle contracts and sends the blood out into the arteries to take oxygen and nutrients to the rest of the body. 

To keep blood from going back into the atrium when the ventricles contract and to force blood to go out of the heart, there are one-way valves between the atrium and the ventricle on both sides of the heart.  The valve between the left atrium and left ventricle is called the mitral valve.  The valve between the right atrium and right ventricle is called the tricuspid valve.  The proper functioning of these valves are critical to maintaining adequate heart function. 

If they mess up then less blood leaves the heart (some blood goes into the atrium when the ventricle contracts instead of leaving the heart) and, thus, more blood remains in the heart.  The body responds to receiving less blood by demanding the heart increase its function.  The heart does so but as the valves get worse and worse, less and less blood leaves the heart for the body.  Eventually, the heart can no longer properly deliver blood to the rest of the body and the animal dies.

TVD is a congenital (that is, it is present at birth as a result of genetic or developmental problems) defect that occurs in Labrador Retrievers and some other breeds.  In this condition, the tricuspid valve (the valve between the right atrium and right ventricle) is not properly formed.  TVD ranges in severity from very mild to very severe.  The very mild to moderate cases may not ever show any clinical signs of disease and, thus, no one knows they have this problem.  They live happy, healthy, active lives.  The problem arises with these individuals not because of any problems to themselves but because if this problem is inheritable, their offspring might have the problem and, if so, often have a more severe form of the disease.

Individuals affected by a more severe form of the disease are unable to have a properly functioning right side of the heart and usually develop right-sided congestive heart failure.  With medical management these individuals can survive for a period of time (few month to couple of years).  Many breeders of Labradors are working to eliminate this
problem from breeding stock with the hope that it will then no longer be a problem.   Dogs are checked using either Auscultation or Color Doppler by a board certified veterinary cardiologist.

Congestive Heart Failure
Anything that causes the heart to not be able to adequately maintain blood flow can cause congestive heart failure (CHF) over a period of time.  Typically, CHF is divided into left-sided and right-sided to denote which side of the heart has the problem.  If both sides do then it is called bilateral CHF. 

Left sided CHF is characterized by a failing left side of the heart.  Since the left side of the heart takes blood returning from the lungs and sends it to the body, the first place affected by a failing left heart are the lungs. Blood backs up in the veins of the lungs causing fluid to leak out into the lung.  This leads to respiratory problems and is typically characterized by coughing in the dog.  As it progresses the dog suffers worse and worse respiratory distress, and if untreated, often dies from the respiratory complications. 

In right-sided CHF the blood backs out in the veins returning blood from the body.  Thus, the fluid leaks out into the rest of the body causing limb and abdomen swelling.  Because fluid accumulation is a component of both types of CHF, a diuretic is given to encourage removal of this fluid.  Other drugs are given to reduce the amount of work the heart has to do and to aid the heart in pumping the blood better.  Typically, dogs can live months to years with CHF given proper medical, nutritional (low salt), and management (low exercise) treatment.  

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