Patent Ductus Arteriosus

OVERVIEW: 

 

Patent Ductus Arteriosus (PDA) is the most common congenital heart disease found in dogs.  Without surgical correction over 60% of dogs that are diagnosed with a left-to-right shunting patent ductus arteriosus will die from complications. The most commonly affected breeds include Toy/Miniature Poodles, Collies, Bichon Frises, Pomeranians, Cocker spaniels, Chihuahua, Maltese, German shepherds, Irish setters, Keeshounds, and Shetland Sheep dogs.  This disease is more prevalent in females than males (2:1).

 

In order to understand more about patent ductus arteriosus it is important to first understand the purpose of the ductus arteriosis.

 

During pregancy, it is the mothers body that is responsible for cleansing and oxegentation of  the blood that is supplied to the fetus in order for it to grow.  Since it is the mothers organs that are providing for the fetus, many of the fetal organs such as the liver and lungs are shunted off or bypassed as their operation is not necessary for the sustaiment of life.  The name of the shunt responsible for for shunting off or bypassing blood away from the non-operational, collapsed fetal lungs is the ductus arteriosus.

 

The ductus arteriosis allows oxgenated fetal blood to pass from the pulmonary artery (the main artery that takes blood to the lungs) to the descending aorta (the main artery responsible for supplying the entire body), thus shunting blood away from the non-functional fetal lungs. In mammals the normal response of the body is to close off the ductus arteriosus in response to the animal breathing on its own. This occurs through necrosis and fibrosis of the ductus arteriosus during the first few weeks of life. Although, the ductus arteriosus of animals less than four days old may not be fully closed it should close off entirely within seven or eight days of birth.

 

When this fails to happen, the resultant condition is called patent ductus arteriosus (PDA);  since the vessel has not closed and remains patent  (not blocked or open) resulting in the irregular transmission of blood between the aorta and the pulmonary artery.  There are two forms of Patent Ductus Arteriousus.  The first and most common form of this condition is called left to right patent ductus arteriosus in which the aortic pressure is higher than pulmonary artery pressure throughout the cardiac cycle, and blood shunts continuously from the aorta to the pulmonary artery. Whereas, the second and least common form of this condition  right-to-left, or reverse patent ductus arteriosus (rPDA) will have a right-to-left flow of blood from the pulmonary artery into the aorta resulting in a massive volume overload and eventual left-sided congestive heart failure.

 

After birth, changes in heart pressure in response to the animal utilizing its own organs for its survival result in the blood moving in the opposite direction.  With left to right Patent Ductus Arteriosus this allows blood to flow from the aorta through the patent ductus arteriosus into the pulmonary artery and into the lungs. The increased flow of blood into the lungs through the unclosed or patent ductus arteriosus causes the pressure in the blood vessels of the lungs to increase which pushes fluid into the air spaces (alveoli) of the lungs. This abnormal fluid accumulation interrupts movement of oxygen through the lungs, resulting in shortness of breath. This abnormal build up of fluid in the air sacs of the lungs is called pulmonary edema. 

 

This continuous flow of blood into the pulmonary artery will also cause an audible heart murmur and the increased return of blood to the left atrium and left ventricle. This increased return of blood causes volume overloading on the left side of the heart and enlargement of the left ventricle. If the overloading continues, the left atrium will also begin to enlarge which could cause the mitral valve; the valve controlling flow from the left atrium to the left ventricle to become completely non functional. In most cases the final result of patent ductus arteriosus is death due to heart failure.
 

SIGNS & SYMPTOMS: 

 

  • With some pets a heart murmur when the pet is young may be the only sign of PDA.
  • Coughing
  • Collapse
  • Intolerance to exercise
  • Apathy
  • Labored Breathing
  • The presence of seizures or episodes of fainting may indicate right to left shunting Patent Ductus Arteriousus.
  • If left untreated clinical signs of Patent Ductus Arteriosus usually appear within the first year.
  • In general the severity of clinical signs is in correlation to the degree of heart failure present.

 

 

DIAGNOSIS & TESTS: 

 

  • The gums will be pink, in the absence of severe build-up of fluid in the lungs from heart failure.
  • Performing an ECG of the heart may show visible evidence of left ventricle and atrium enlargement.
  • Enlargement of the left arterial and left ventricle may be visible through the use of X-rays. X-rays may also show overcirculation of the lungs, and dilatation of the descending aorta and pulmonary artery.
  • Evaluation with ultrasound will often times reveal enlargement and dilation of the pulmonary artery and aorta. In most, but not all cases the ductus can be imaged.

 

CONVENTIONAL TREATMENT & MANAGEMENT: 

 

  • In cases where congestive heart failure has developed, the patient will be stabilized with medication prior to surgery.
  • Tying or binding the ductus arteriosus closed with a ligature or suture (surgical ligation) is the treatment of choice for patent ductus arteriosus. Sutures will be placed around the patent ductus and carefully ligated (tied or closed).
  • Heart failure is instantly reversed with completion of the procedure.
  • The post surgical prognosis for pets is excellent; with most animals returning to a completely normal activity level just weeks after surgery.   If surgery is not performed, most pets with patent ductus arteriosus will die of heart failure.

 

POTENTIAL COMPLICATIONS: 

 

  • As with all surgeries there is the potential for medical complications. Certain breeds of dog are known to have an acute sensitivity to anesthesia* that could result in anesthetic death. A knowledgeable veterinarian that is familiar with the breed, using monitoring devices that measure blood pressure, EKG, pulse oxymetry, inspiratory and expiratory carbon dioxide levels, and respiration rate will minimize the risk of problems with anesthesia.
  • Tearing of the backside of the ductus as it is being ligated has been known to happen occasionally. The resultant bleeding could cause the death of the pet. In cases where the bleeding is not overly severe, but resumes as the repair continues, it may need time to naturally heal and ligation of the ductus may be delayed to another time.
  • Around 1.5% of animals with patent ductus ligation have recanalization of the ductus. This is a condition in which the body naturally forms new canals or paths, especially blood vessels, through an obstruction such as a clot or in this case a litgated ductus. When this happens the murmur will usually return within two months of operation.  The procedure to repair a recanalized ductus is far more difficult than initial surgical ligation and requires that the ductus be clamped and cut with a blade and that each end be sutured together.

 

 *Anesthetic sensitivity can be attributed to a number of factors including extremely low body fat, diminutive size and dogs with the genetic mutation known as MDR-1. The breeds considered to be at the greatest risk for complications related to anesthesia are the Afghan Hound, Akita, American Eskimo, Anatolian Shepherd, Baluchi Hound, Belgian Shepherd (tervueren), Borzoi, Bouvier des Flandres, Chow Chow, Deer Hounds, Filia Brasileiro, Great Pyrenees, Greyhound, Ibizen Hound, Komodor, Kuvasz, Malamute, Maremmas, Mastiff, Papillon, Pharaoh Hound, Pomeranian, Saluki, Shar-pei, Siberian, Siberian Huskie, Tazi, Tibetan Spaniel, Toy breeds, Vizslas, Wheaton Terriers, Whippet, and Wolf Hounds.