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. Within 24 hours 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." If only partial closure occurs, the condition is called ductus diverticulum. The principal cause of a PDA is site-specific defect of the smooth muscle within the ductus, in combination with excessive elastic tissues within the ductus resulting in incomplete constriction of the lumen. Patent ductus arteriosus is the second most common congenital cardiac malformation, second only to subaortic stenosis; however, it is the most commonly diagnosed cardiac defect that routinely requires intervention. Without correction, it typically leads to mitral valve regurgitation and left-sided congestive heart failure.4 Most dogs treated before age 6 months go on to lead completely normal lives.

Occurring in all species and diagnosed at any age, PDA is most commonly recognized in young animals. Small breed dogs tend to be affected most frequently. Breeds at higher risk include the Miniature Poodle, Collie, Pomeranian, Cocker Spaniel, Chihuahua, Maltese, German Shepherd Dog, Irish Setter, Keeshound, and Shetland Sheepdog. The condition is about four times more common in female puppies than in male puppies. The tendency for normal dogs to produce affected offspring and teh severity of the disorder among their affected offspring depends on how closely the normal dog is genetically related to the affected dog. Normal dogs that are closely related to the affected dogs produce more than three times the incidence of affected offspring, and more than four times the incidence of severely affected offspring, when compared with normal dogs that are unrelated to affected dogs.



There are two types of patent ductus arteriosus. 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 this type of 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.

Structure of the human heart

Patent ductus arteriosus often is an incidental finding in a young animal presented for vaccinations or surgery and the animals do not usually show clinical signs at this time. If clinical signs are present, they usually include coughing, labored breathing, exercise intolerance, decreased appetite, and collapse. 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. If the PDA is left untreated, clinical signs usually appear within one year. 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. Transthoracic echocardiography is the diagnostic technique of choice for the initial evaluation of dogs with suspected congenital heart diseases. The advantages of echocardiography include noninvasiveness, high accessibility, and low cost.3 Multidetector-row computed tomography (MDCT) is a new, reliable and noninvasive tool for diagnosing PDA. Surgery is more successful if done in the young dogs, before permanent heart damage has occurred.

Dogs with heart failure are initially treated with a diuretic to remove excess fluid. The closure of the ductus is performed either by ligation during open-chest surgery or by insertion of a special plug during cardiac catheterization procedure. Ligation is a very effective procedure in the hands of a skillful surgeon with a success rate of up to 95% and a mortality rate of less than 2%, but a major disadvantage is the invasiveness of the procedure. One of the major complications of the catheterization procedure is plug migration, which has an incidence rate of 3%. The most common site for migration of devices is the main pulmonary artery and lungs. Following successful device implantation, repeat echocardiography and radiography should be completed the day after surgery and are recommended 3 to 6 mo postoperatively to determine if there is any persisting ductal flow and to reassess heart size.4

References

  1. Cunningham's Textbook of Veterinary Physiology. Bradley G. Klein PhD
  2. An Introduction to Veterinary Genetics. Frank W. Nicholas
  3. Multidetector-row computed tomography of thoracic aortic anomalies in dogs and cats: Patent ductus arteriosus and vascular rings
  4. Treatment of patent ductus arteriosus by the use of an Amplatz canine ductal occluder device




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