Patent Ductus Arteriosus
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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Key Points

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.

      

 

Clinical signs

  • Coughing
  • Labored breathing
  • Exercise intolerance
  • Collapse
  • 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.

 

Diagnosis

  • 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.

 

Treatment options

  • 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.

 

Potential complications

  • 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.

 

Prognosis

  • 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.

Frequently Asked Questions After Surgery

When should my dog have the first bowel movement after surgery?

  • Many dogs will not have a bowel movement for the first 4 to 5 days after surgery
  • Reasons that a dog will not have regular bowel movements after surgery include:
    • The dog has been fasted prior to surgery
    • Dogs do not eat well during the hospital stay
    • They frequently do not eat well when they go home
    • They are fed highly digestible food that produces little stool
    • Pain medication that contain narcotics (such as morphine, fentanyl patches, and tramadol) can be constipating
  • If a pet does not have a bowel movement on the 5th day of being home, a stool softener such as metamucil can be fed
    • Dose of metamucil is 1 tsp per 25 Kg mixed in with each meal (canned dog food); feed immediately after mixing, as the metamucil will gel the food and may make it less palatable

My pet had surgery and will not eat.  What can be done?

  • Dogs
    • Most pets will not eat their regular dog food after surgery, especially if it is kibble.
    • Offer a cooked diet having a 1:1 ratio of a protein source and carbohydrate source.  The protein source can be any meat (example: chicken breast, turkey breast, lean hamburger) that is low in fat and should be cooked (drain off all fat after the meat has been cooked).   The carbohydrate can be pasta, potato or white rice.
    • Try canned dog food; to enhance the flavor sprinkle a very small amount of garlic powder or chicken or beef broth (Chicken-in-a- MugTM or Beef-in-a-MugTM products)
    • Try Gerber strained meats for babies such as the chicken, beef, turkey, or veal
    • Try Hill's A/D diet available at most veterinary hospitals
    • Hand feeding: place a small amount of food in the mouth so that your dog gets the flavor
    • Warm the food slightly in a microwave, as the food will be more aromatic; stir the food before feeding and test the temperature on the bottom side of your wrist; it should only be luke warm.
    • Remember that most pets will not eat the first day or two after they get home from surgery
  • Cats
    • Offer smelly foods that contain fish such as tuna or smelly cat foods
    • Try Gerber strained meats for babies such as the chicken, beef, turkey or veal
    • Hand feeding:  with your finger place a small amount of food on the roof of your cat's mouth; use a syringe to get soft food into the mouth
    • Warm the food slightly in a microwave as the food will be more aromatic; remember to stir the food before feeding and test the temperature; it should be only luke-warm
    • Some cats will only eat dry food, try kibble if your cat normally has been fed that food
    • Petting and stroking your cat frequently will help to stimulate appetite
    • Remember that most pets will not eat the first day or two after they get home from surgery
    • Appetite stimulants such as cyproheptadine may be helpful
    • If your cat refuses to eat anything for 7 days a stomach tube or nasogastric tube should be placed to provide nutrition so that a serious liver problem (hepatic lipidosis) does not develop

My pet is vomiting.  What can be done?

  • The first thing for you to discern is whether your pet is vomiting or regurgitating.  Both will result in fluid or food being brought up.  Vomiting always will have heaving or retching of the abdomen prior to expulsion of the vomitus.  Regurgitation is not associated with heaving and the pet usually just opens the mouth and fluid or food will be expelled.  Usually the regurgited material will be clear or brown colored fluid. 
  • Next is to identify the cause of the vomiting or regurgitation.
  • Causes and treatment of vomiting after surgery
    • When some pets return home after a stay in the hospital they may drink excessive amounts of water at one time and then vomit; if this appears to be the case, the water should be limited to frequent smaller amounts.
    • Medications such as antibiotics, narcotics or nonsteroidal anti-inflammatory medication commonly cause vomiting after surgery.  In order to see which medication is causing the problem, the administration of each drug should be separated 2 hours apart.  Usually the pet will vomit or appear nauseated (drooling and sick look) within 1 hour of administration of the medication that they are sensitive to.  The antibiotic in some cases may be changed to a different one, or may be discontinued. 
    • Stomach upset from anesthesia is a potential cause of vomiting and will pass within a couple of days. 
    • An uncommon cause of vomiting after surgery is internal organ failure.  Blood testing will confirm this problem. For this reason vomiting should not be ignored if it persists for more than 24 hours.
    • If your pet had surgery of the bowels or stomach, vomiting is always a concern, as it may indicate that infection of the abdominal cavity, called peritonitis, is present.  Do not ignore this sign.
    • Symptomatic treatment of vomiting involves withholding food for 12 to 24 hours, then introducing small amounts of bland food such as rice and lean cooked hamburger, if your pet does not vomit after that then gradually wean him/her back onto the regular diet after 3 days.  In order to decrease the acidity of the stomach, Pepcid AC 0.5 mg/kg can be given by mouth twice daily for 5 days.  Metoclopramide and Cerenia are good anti-vomiting medications for dogs and cats.  You should always consult a veterinary healthcare professional before administering medication.
  • Causes and treatment of regurgitation after surgery
    • The most common cause of regurgitation is reflux of acid from the stomach into the esophagus while your pet is under anesthesia.  Acidic fluid from the stomach can cause a chemical burn of the esophagus and result in a bad case of heart burn, called esophagitis.  This results in poor motility of the esophagus, therefore water and food will accumulate in this structure.  In most cases, esphagitis is self-eliminating and will resolve within two or three days. 
    • If the esophagitis is severe the esophagus may develop one or more strictures.  A stricture is a narrowing or stenosis of the esophagus and does not allow passage of food down the esophagus, in regurgitation that lasts longer than one week.  This problem should be brought to the attention of your pet's doctor within the first two weeks so that it can be treated by ballooning the stricture (minimally invasive procedure, as it is done with the aide of an endoscope).  If an esophageal stricture is chronic surgery is needed.
    • Symptomatic treatment of regurgitation caused by esophagitis includes feeding bland food, and administering a coating agent (sucralfate) and an acid blocker (omeprazole or other).  Consult a veterinary health care professional if the regurgitation continues for more than a couple of days.

How do I know that my dog is in pain following surgery?

  • Signs of pain include
    • crying
    • biting if you get near the surgical site
    • grimacing (lips are pulled back and the the dog looks anxious)
    • tragic facial expression
    • panting
    • restlessness and unable to sleep; pacing
    • if abdominal surgery was done the pet will not lie down on the incision, or will continually sit up in spite of appearing very tired
    • the worst pain will be for the first 2 to 3 days after surgery

What can I do to control my dog's pain?

  • Narcotic medications that control pain: tramadol, butorphanol, Duragesic (fentanyl patch)
  • Anti-inflammatories used to control pain: Deramaxx, Rimadyl, Previcox, or Etogesic
  • If an orthopedic surgery has been done cold packing the surgical site may be helpful
    • A cold pack may be a pack of frozen peas, crushed ice in a Ziploc bag, or a cold gel pack; place a thin barrier between the skin and the cold pack.  An alternative to a cold pack is to freeze water in a styrofoam cup; after frozen cut the bottom of the styrofoam cup out. Cool the surgical site around the incision by rubbing the exposed ice directly on the skin in a circular pattern.  Cooling the surgical site helps to numb the area.

How do I know that my cat is in pain following surgery?

  • Pain is more difficult to assess in cats versus dogs, as signs can be more subtle and they usually do not vocalize when in pain
  • Signs of pain in a cat include the following:
    • biting if you get near the surgical site
    • growling or deep cry
    • not wanting to eat
    • hiding and not wanting to be near owner (remember that this could also be caused by the cat just being upset about leaving home and coming back)

What can be done for pain at home for my cat?

  • Pain medication such as buprenorphine or a Duragesic (fentanyl) patch
  • Tylenol will kill a cat as they lack abundant glutathione enzyme in the liver
  • Anti-inflammatories can be used, but the dose is much less than dogs

Is it okay for my pet to lick the incision?

  • If a dog licks the incision, the healing process may be delayed.
  • Licking can remove stitches and cause the incision to open
  • Licking can become a severe habit that is difficult to break
  • Licking can cause infection as the mouth has many bacteria
  • Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your pet from licking the following can be tried:
    • Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    • Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    • A tee shirt can be used to cover an incision on the chest or front part of the abdomen; gather the waist of the shirt up over the dog's back and wrap an elastic band around this part of the shirt.
    • A bandage or sock can be used to cover an incision on a limb; fasten the top of the sock to the dog's limb with tape.
    • Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    • Bitter Apple and Liquid HeetTM (obtain this from a drugstore...it is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
    • Antipsychotic medication in some cases is needed

Board-certification by the American College of Veterinary Surgeons

What does it mean?

  • Four years of advanced training in surgery beyond the Doctor of Veterinary Medicine Degree

  • Experience in the development of new surgical treatments

  • Rigorous examination by the American College of Veterinary Surgeons to ensure competency in advanced surgical techniques

  • Assurance that a veterinarian is a surgical specialist

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