Mitral Valve Dysplasia (MVD) is also known as Mitral Valve Disease, Mitral Valve Disorder, Mitral Valve Malformation, Mitral Dysplasia, Mitral Systolic Murmur, Cardiac Valve Disease (CVD), Endocardiosis, Atrioventricular Valve Endocardiosis, Chronic Degenerative Valvular Disease, Chronic Valvular Disease, Chronic Mitral Valve Insufficiency, Myxomatous Atrioventricular Degeneration, Chronic Valvular Fibrosis, Acquired Mitral Regurgitation or Insufficiency, and Mitral Valve Defect.
Mitral Valve Dysplasia is a condition in which a defect in the mitral valve (the left atrioventricular valve) causes backflow of blood into the left atrium, or mitral regurgitation. Chronic mitral regurgitation leads to volume overload of the left heart, which results in dilatation of the left ventricle and atrium. When mitral regurgitation is severe, cardiac output decreases, which results in signs of cardiac failure. Severe mitral regurgitation can also result in pulmonary venous congestion and left-sided congestive heart failure (CHF). Dilatation of the left-sided chambers predisposes affected animals to arrhythmias. In some cases, malformation of the mitral valve complex causes a degree of valvular stenosis as well as insufficiency.
Mitral valve insufficiency is age- and breed-related, with older, small-breed dogs demonstrating a higher incidence. There is also a slight predisposition among male dogs. This disease is the most common acquired cardiac disease in older dogs, affecting over one third of dogs greater than 10 years of age. In some breeds however, mitral insufficiency develops at a much younger age, due to an inherited predisposition for this disorder. In fact, in some breeds, abnormal development (dysplasia) of the valve has been identified in embryos.
Mitral valve murmurs are graded from the mildest and least audible to the loudest and most turbulent. The loudness of the murmur usually indicates the severity of the disease.
Grade 1: Murmur can be heard with a stethoscope in a quiet room.
Grade 2: Can be consistently heard with the stethoscope.
Grade 3: Murmurs are louder and are heard as soon as the stethoscope is applied.
Grade 4: Quite loud, and the vibration can be felt with fingertips without a stethoscope.
Grade 5: Murmur is louder, with a precordial "trill".
Grade 6: So loud it can be heard with the stethoscope removed from the chest, or even without using the stethoscope.
Age at onset: Abnormal heart morphologies have been seen observed during embryonic stages, however this disease is more commonly seen in dogs over the age of 10 years.
Breeds Affected: Mitral valve disease is the most common heart disorder in older dogs of all breeds. In general, small breeds are most often affected and some studies show a greater incidence in males than in females
Symptoms: Dogs have a an increasingly loud heart murmer, abnormal heart rhythm, reduced tolerance for exercise, difficulties in breathing, or a cough at night or at rest. They may faint, show weakness, or collapse.
Genetics of Mitral Valve Dysplasia: The genetics of mitral valve dysplasia are not well understood yet, however research studies indicate it is an inherited trait.
Mitral Valve Dysplasia in Humans: Mitral valve disease is a genetic disorder in humans that is highly similar to the disease in dogs. In addition, Ebstein's anomaly in humans is thought to be share similarities to tricuspid valve dysplasia.
Below is a video produced by the American College of Veterinary Internal Medicine featuring Teresa DeFrancesco, DVM, DACVIM (Cardiology), DACVECC, speaking with Steve Dale on the topic of Mitral Valve Disease in dogs.
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