Heart Valve Narrowing (Mitral and Tricuspid) in Dogs

There are four chambers in a heart which are known as atria (upper two chambers) and ventricles (lower two chambers). There are valves present between each pair of upper and lower atrium and ventricle. The valve between left atrium and ventricle is called mitral valve while that between right atrium and ventricle is known as tricuspid valve. These valves are responsible to block backward flow of blood from ventricles into atria when ventricles contract. 

Malformation in mitral valve, which is located on the left side of the heart, affects blood flow to the lungs whereas abnormalities in tricuspid valve, located on right side of the heart, affect blood flow to the rest of the body.

Stenosis is the narrowing of either of these valves. It can be a congenital condition (present at birth) or it can be due to bacterial heart muscle infection or heart cancer. The tricuspid and mitral valves are responsible to block backflow of the blood into atria when ventricles contract. Leaking of the valve(s) allows backflow of blood into the atria. This flow of blood going the wrong way is called "regurgitation".  Too much volume and pressure in the atrium (either left or left) causes enlargement of left or right atrium. Consequently, an increase in the diastolic pressure gradient between the atrium and the ventricle occurs (the pressure gradient is the period in which the heart's chambers dilate and fill with blood – diastole of the ventricles follows diastole of the atria).

High blood pressure in the lungs, coughing and trouble breathing during exercise are symptoms of mitral valve narrowing (stenosis) where as tricuspid valve stenosis is characterized by swelling of the legs and paws, and a possible enlarged liver. 

New Foundland and Bull terrier breeds are more commonly affected by mitral valve stenosis while Old English Sheepdogs and Labrador Retriever breeds are at a higher risk of tricuspid valve stenosis. Congestive heart failure can occur due to abnormality of either of the valves.

Common symptoms associated with mitral or tricuspid valve stenosis include

Exercise intolerance

Fainting (syncope)

Trouble breathing while exercising

Coughing (mitral valve narrowing)

Pale or bluish skin color (cyanosis)

Fluid in the abdomen, swelling (tricuspid valve stenosis)

Stunted growth

Spitting up blood

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