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Tricuspid and Mitral Valve Dysplasia Rebecca E. Gompf, DVM, MS, DACVIM (Cardiology) BASIC INFORMATION Description The mitral valve is the valve between the two chambers on the left side of the heart, and the tricuspid valve separates the two chambers on the right side of the heart. Valves function to keep blood flowing in one direction through the heart and to the lungs and body. Dysplasia is malformation of the valve that results in stiffness and decreased ability to open properly, leakage, or both. Dysplasia is a congenital defect that is present at birth. When dysplasia causes the valves to leak, blood flows in the wrong direction. This increases the workload of the heart and makes the affected side dilate. Eventually right- or left-sided heart failure may occur. If the valve is also stiff and does not open adequately, the large chamber (ventricle) on the affected side of the heart does not fill properly with blood. This also contributes to heart failure. Causes Most of these defects are spontaneous and occur randomly. They may be inherited in some breeds, such as the Labrador retriever, bull terrier, German shepherd dog, golden retriever, Great Dane, mastiff, Newfoundland, Old English sheepdog, Rottweiler, and Weimaraner. They have also been reported in cats. Clinical Signs Most puppies and kittens have no signs, but a murmur may be discovered on physical examination. If the dog or cat is older, signs of heart failure may be present. With mitral dysplasia, most animals are normal until they develop signs of left heart failure by 6-9 months of age. Exercise intolerance, lethargy, labored breathing, increased respiratory rate, and coughing may be noted. Animals with mild tricuspid dysplasia may never develop signs. Animals with more severe tricuspid dysplasia are often normal until their right atrium enlarges and develops an abnormal heart rhythm called atrial fibrillation. This often occurs between 4 and 7 years of age. Once atrial fibrillation is present, exercise intolerance, lethargy, and abdominal fluid may develop. Cats may develop fluid in their chest and have trouble breathing. If the animal has a second congenital heart defect, such as an atrial septal defect, fatigue and bluish discoloration of the gums may be noted. Diagnostic Tests If a heart murmur is discovered, chest x-rays and an echocardiogram (heart ultrasound) with Doppler capabilities are often needed to identify the exact defect and determine its severity. An electrocardiogram (ECG) is done if an arrhythmia is detected. TREATMENT AND FOLLOW-UP Treatment Options Treatment is usually given to animals that are in heart failure. Once left or right heart failure develops, the following medications may be started: • An angiotensin-converting enzyme (ACE) inhibitor, such as enalapril or benazepril, helps control fluid accumulation and improves the function of the failing heart. The main side effect is weakness from hypotension (low blood pressure). • Diuretics, such as furosemide or thiazides, are used to decrease fluid accumulation in the lungs or other parts of the body and may be combined with spironolactone (another diuretic). Side effects include dehydration and electrolyte abnormalities. These drugs also increase water consumption and urine output, so provide plenty of water at all times. • Pimobendan increases the heart’s ability to pump blood and may improve the animal’s quality of life. Most dogs and cats tolerate this drug very well, but watch for any decrease in appetite, vomiting, or diarrhea. • If the animal is in atrial fibrillation, digoxin may be used alone or combined with a beta-blocker, or a calcium channel blocker (diltiazem) may be used to slow the heart rate. If the dysplastic valve is stiff and does not open properly, your animal may be referred to a specialist for possible balloon dilation. In the United States, surgery to repair or replace these valves can be done at only a few veterinary specialty facilities. Follow-up Care Yearly echocardiograms are often recommended for animals with mild dysplasia to monitor their heart function and any changes in the heart. More frequent monitoring and testing are needed for animals in heart failure. (See also the handouts on Congestive Heart Failure.) Prognosis Animals with mitral valve dysplasia usually develop left heart failure before 6-9 months of age and rarely survive past 1 year even with therapy. Animals with mild tricuspid dysplasia typically have no problems, but dogs with more advanced tricuspid dysplasia may develop atrial fibrillation between 4 and 7 years of age. Once atrial fibrillation develops, right heart failure eventually occurs. With medical management, these dogs usually live an additional 6-12 months. IF SPECIAL INSTRUCTIONS HAVE BEEN ADDED, THEY WILL APPEAR ON THE LAST PAGE OF THE PRINTOUT. Copyright © 2011 by Saunders, an imprint of Elsevier Inc. All rights reserved.