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Patent Ductus Arteriosus
Fetal dogs have a short, broad vessel called the ductus arteriosus, which sends blood from the right ventricle of the heart to the aorta, thus bypassing the lungs. Shortly after birth the vessel should close naturally. If it does not close, normal circulation is impaired. This congenital heart defect is called patent ductus arteriosus (PDA), patent meaning "open." Cardiac surgery may be required to correct the problem. Affected breeds include Miniature Poodle, Collie, Pomeranian, Cocker Spaniel, Chihuahua, Maltese, German Shepherd, Irish Setter, Keeshound, and Shetland Sheepdog.
Findings suggest that the PDA is caused by a genetic defect in the structure of the ductus arteriosus that is similar or identical to that in the Poodle. The relatives of dogs with PDA should be screened for evidence of PDA. Dogs with PDA should not be used for breeding.
Types of Patent Ductus Arteriosus
There are two types of PDA. The left to right is the typical form of PDA in which the aortic pressure is higher than lung artery pressure, and blood shunts
continuously from the aorta to the lung artery. This results in a continuous heart murmur, and increased size of the heart. Without surgical correction, approximately 64% of the dogs diagnosed with left-to-right shunting PDA will die from complications within one year of diagnosis. Some dogs with modest shunts will survive to maturity, and a few may live 10 years or more. Right to left, or reversed PDA, is an uncommon condition which occurs when there is an increase in lung vessel pressure. Many owners do not recognize obvious clinical signs in their pet during the first 6-12 months of life. Animals with reversed PDA often live 3-5 years; a few survive beyond 7 years.
Signs
Clinical signs of PDA may include coughing, labored breathing, exercise intolerance, collapse, and decreased appetite. If the ductus is small, there may be no signs at all. The severity of these signs is related to the degree of heart failure. Dogs with heart failure are initially treated with a diuretic, a medication that promotes urination, to remove excess fluid. If the PDA is left untreated clinical signs usually appear within one year.
Diagnosis & Treatment
The diagnosis is usually made by listening to the heart and detecting continuous heart murmur, which can be confirmed by examining a chest X-Ray and evaluating the heart echocardiogram. Surgery is more successful if done in the young dogs, before permanent heart damage has occurred.
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