Mitral Valve Insufficiency (Endocardiosus) in Dogs

What is Mitral Valve Insufficiency?

The mitral valve separates the left atrium (top chamber) and the left ventricle (bottom chamber) of the heart. Blood comes into the left atrium from the lungs and goes through the mitral valve into the left ventricle. When the left ventricle contracts to push blood out through the aorta to the rest of the body, the mitral valve closes, thus preventing any backflow back into the left atrium. Mitral valve insufficiency occurs when this valve does not close properly (due to age degeneration or infection most commonly) thus causing some blood to go back up into the left atrium when the left ventricle contracts.

How is it diagnosed?

The most common presenting sign is a murmur when listening to the heart with a stethoscope. A murmur is the sound that occurs (much like a “woosh” sound instead of a crisp beat sound) because of the turbulent blood flow that goes back up through the mitral valve. Murmurs are normally graded from 1-6 depending on a variety of factors. Once a murmur is picked up on clinical examination, your vet may ask a few questions to try and establish whether or not the mitral valve insufficiency is causing clinical signs or not. The most common clinical signs are:

  • Coughing
  • Exercise intolerance
  • Shortness of breath
  • Slight lethargy

Once this is determined, it is normally necessary to do some tests to ascertain how serious the problem is and whether any therapy is required or not, and if so, what type of treatment would be best. The most common tests done are an ultrasound, an x-ray and often also an ECG. Blood tests may sometimes also be necessary to see if all the organs are getting enough blood supply and whether there are any underlying problems. 

What is a heart ultrasound and is this necessary?

A heart ultrasound or an echocardiographic examination, is a scan that is done on the heart to establish a few things. During the procedure one can actually visualize the heart contracting and can measure the blood flow back through the valve. There are many other measurements taken during a heart ultrasound that give us a much better picture of the entire problem and what treatment would be best for your pet, for example:

  • Measure how much the heart muscle is actually contracting – this can tell us if there is enough compensation for the valve problem and whether we need to give something to help the heart muscle or not.
  • Measure the blood outflow through the aorta – this is a very important measurement because it tells us if there is enough output from the heart to maintain blood pressure and blood flow to all the organs.
  • Measure the size of all the chambers of the heart
  • Measure and visualize exactly how much blood is going back through the valve
  • Can visualize the actual valve and measure the thickness 

All of these put together will enable us to decide on the best approach toward treatment and management of your pet. 

What is the treatment?

The only treatment that reverses and solves the problem totally is a valve replacement. In humans this is a common procedure, but in pets it is not performed due to many problems (different sized hearts and thus valves, patients have to be on a heart-bypass machine during procedure and prohibitive costs). Treatment is thus aimed at relieving any clinical signs (mainly coughing) and helping the heart cope with the problem. In the early stages where no clinical signs are present, treatment is generally not necessary. If the ultrasound suggests that treatment may be beneficial (even in the absence of clinical signs), then conservative management and treatment is normally required. In advanced stages, many treatments are normally required. The most common drug used is a diuretic, to remove any fluid build up on the lungs and thus alleviate the coughing. Other drugs that may be used include vasodilators (drop blood pressure) and specific heart medications to help the heart contract better or control the rhythm of the heart. 

What is the prognosis?

Many pets with mitral valve insufficiency live normal, happy lives for an extended period of time.  The time it takes for development of problems is extremely variable. Although the condition is irreversible, with the advancement of diagnostics and treatments, the treatment for many cases can be very rewarding.

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