A patent ductus arteriosus is a normal structure found in the unborn human and animal, however, by the third day after birth it usually closes
A PDA shunts blood back to the lungs and heart, which results in heart failure
Corrective surgery is more successful if done in the young animal, before permanent heart damage has occurred
Surgery is relatively simple and will bring the patient out of heart failure almost immediately
What is a Ductus Arteriosus?
- The unborn cat and dog have a system of shunting blood through special vessels so that certain organ systems do not have to work. In the fetus certain organs such as the lungs and liver are not required to function, as the mother does the cleansing and oxygenation of the blood via the placenta. One shunting system shunts blood to bypass the liver. Another shunting system causes blood to bypass the lungs. This shunt or large vessel is called the ductus arteriosus.
- The Ductus Arteriosus is derived from the left sixth aortic arch. It shunts blood from the pulmonary artery (main artery that takes blood to the lungs) to the descending aorta (main artery that feeds the entire body), an action that diverts flow from the collapsed fetal lung. In a normal dog or cat the ductus arteriosus closes in response to the pup or kitten beginning to breathe on its own. Although the ductus arteriosus may be patent in pups less than four days of age it generally closes by seven or eight days after birth.
What is a Patent Ductus Arteriosus?
- If the ductus arteriosus fails to close after birth it is called a patent ductus arteriosus. As mentioned above, the ductus arteriosus allows blood to pass through the heart and then bypass the lung system. After birth the pressures change in the heart so that the blood moves in the opposite direction, from the aorta into the shunt, then into the lungs. This causes increased amount of blood flow to the lungs and can cause fluid to build up in the lungs, thus results in labored breathing.
- The continuous flow of blood into the pulmonary artery causes a continuous heart murmur, increased blood flow into the lungs, and increased return of blood to the left atrium and the left ventricle. Volume overloading of blood on the left side of the heart causes enlargement of the left ventricle. If the overloading gets severe enough, the left atrium also gets enlarged and could cause the mitral valve, which separates the left atrium from the left ventricle, to become nonfunctional. The final result of the patent ductus arteriosus is heart failure.
- Here is an illustration of a heart with a patent ductus arteriosus (PDA). The blood from the body (blue) flows through the right side of the heart and into the main artery that goes to the lungs. Blood from the lungs is delivered to the left side of the heart (red) and to the main artery that goes to the body. The connecting vessel labeled PDA allows blood to passes from the left side of the body (red) to the vessel to the lungs (blue), which causes the lungs to be over flooded with blood, thus fluid builds up in the lungs and causes labored breathing.
- Labored breathing
- Exercise intolerance
- The severity of these signs is related to the degree of heart failure.
- Seizures and fainting spells may suggest right to left shunting Patent Ductus Arteriosus.
- Some pets do not have any clinical signs, but a heart murmur is detected when the pet is young.
- If the PDA is left untreated clinical signs usually appear within a year.
- Upon physical exam, the typical cases have a short bounding arterial pulse, a continuous thrill may be felt at the over the chest at the location of the heart, and a continuous heart murmur. The gums are pink unless there is a severe build-up of fluid in the lungs from heart failure.
- ECG of the heart may show evidence of enlargement of the left ventricle and atrium. If the heart muscle is diseased, abnormal heartbeats may be present.
- X-rays may show overcirculation of the lungs, left atrial and left ventricle enlargement and they may show dilatation of the main pulmonary artery and descending aorta.
- Ultrasonic evaluation frequently reveals left-sided heart enlargement and dilatation of the aorta and pulmonary artery. The ductus can be imaged in many, but not in all cases.
- If congestive heart failure has developed, the patient is stabilized with medication prior to surgery.
- The treatment of choice for patent ductus arteriosus is surgical ligation of the ductus. Sutures are placed around the ductus and are carefully ligated by the surgeon. As soon as the PDA is ligated heart failure is instantly reversed. Prognosis with surgery is excellent, and within weeks after surgery the pet’s activity can return to normal. If surgery is not performed, pets having a PDA usually die of heart failure.
- As with any surgery, complications may arise. Even though rare, anesthetic death can occur. With the use of modern anesthetic protocols and extensive monitoring devices (blood pressure, EKG, pulse oxymetry, inspiratory and expiratory carbon dioxide levels, and respiration rate), the risk of problems with anesthesia is minimal.
- Occasionally the backside of the ductus will tear as it is being dissected. This could result in death of the pet. If the bleeding is not too severe, but starts up again as the dissection continues, ligation of the ductus may be delayed to another time.
- Approximately 1.5% of animals with patent ductus ligation have recanalization of the ductus. With this, the murmur returns usually within two months of operation. A recanalized ductus is divided and sutured. This procedure requires reoperation of the same surgical space except this time the ductus is clamped and cut with a blade and each end will be sutured together. This procedure is far more difficult than the ligature procedure and is used mostly by individuals with previous experience in vascular surgery.
- Infection is also an unusual complication as strict sterile technique is used during the surgery and antibiotics are administered.
- Seroma formation or fluid accumulation under the skin incision, although uncommon, can also occur. This problem will resolve with time. Occasionally the seroma or fluid that has build up may require draining.
- The long-term prognosis for dogs and cats treated surgically is good. Most pets are clinically normal following surgery, and overall heart size normalizes. Quiet left or right-sided murmurs are commonly detected immediately following ductus ligation, but usually resolve within 10-14 days after surgery.