Persistent right aortic arch ( vascular ring anomaly )

What is ... ?: 

The term vascular ring anomaly describes several disorders that occur because of abnormal development of the major blood vessels in the chest.  Malformations in these arteries may entrap vital structures, or may be harmless differences that never hamper a dog's health. The most common abnormality is a persistent right aortic arch which develops instead of the left aortic arch that would normally become the permanent aorta, the main blood vessel leading from the heart.  It causes varying degrees of narrowing of the esophagus, leading to digestive problems in weanling puppies.

These anomalies are relatively common in puppies. They do not cause problems in the circulation of blood around the body; however, entrapment of the esophagus and sometimes the trachea can cause regurgitation, unthriftiness, and often aspiration pneumonia.

How is ... inherited?: 

Inheritance is complex. This means a single genetic defect has not been identified that explains all cases, and a genetic test does not yet exist.

What does ... mean to your dog & you?: 

Signs of this condition usually become apparent shortly after weaning, when a puppy begins eating semi-solid or solid food. The partial obstruction of the esophagus causes regurgitation, which is a passive reflux of undigested food, often in a tubular shape, back out the mouth. Dogs with this condition are often excessively thin or even emaciated, and yet often have ravenous appetites. They are prone to aspiration pneumonia, meaning that they may choke on regurgitated food and become ill as a result of inhaled mucus, food, and water.
Vascular ring anomalies like persistent right aortic arches can be corrected surgically. It is important to do so promptly, to reduce the likelihood of permanent damage to the esophagus.  Vascular ring anomalies are never outgrown: they cannot self-correct spontaneously.

How is ... diagnosed?: 

This condition is suspected when a puppy first begins regurgitating within a few days of weaning. It is important to note that regurgitation, which is a passive process, is different from vomiting, which is an active process. Regurgitation involves the puppy producing undigested food and mucus through the mouth with no effort; the pup tilts its head down and the food and mucus simply roll out. This is typical of vascular ring anomalies/persistent right aortic arch if it first occurs just after weaning.  By contrast, vomiting is an active process, meaning there are abdominal contractions ("heaving") and a retching noise when food and mucus are expelled out the mouth.  Vomiting is not a symptom of vascular ring anomalies.  The distinction between regurgitation and vomiting is important because vascular ring anomalies/persistent right aortic arch only ever cause regurgitation, whereas dozens of disorders may cause a pup to vomit.
Chest x-rays are the confirmatory test of choice.  The deviation of certain vital structures, notably the trachea, on X-ray, is conclusive in virtually all cases.  Feeding an X-ray dye called barium was formerly thought to be essential for confirming persistent right aortic arch but is now known to be essentially obsolete.
Chest X-rays also help differentiate vascular ring anomaly/persistent right aortic arch from juvenile diffuse megaesophagus, which is a generalized weakening of the esophagus that many puppies simply outgrow without treatment.
There is no benefit to performing echocardiography (cardiac ultrasound), electrocardiography (ECG/EKG), or other tests of the cardiovascualr system, unless the veterinarian suspects an additional, unrelated heart problem.  Vascular ring anomalies alone do not cause abnormalities on echocardiograms or ECGs.

How is ... treated?: 

Correcting vascular ring anomalies/persistent right aortic arches requires surgery. The operation consists of a thoracotomy (opening the chest) and ligation and transection of the ligamentum arteriosum, the most accessible component of the ring constricting the esophagus. Surgery should be performed as early in a puppy's life as possible, to reduce the likelihood of permanent damage to the esophagus due to chronic distension.
Postoperative care involves feeding a liquid diet with the puppy held upright in a sitting position for some time after feeding, to help the liquid diet pass down to the stomach.  After days to weeks, solid food is gradually reintroduced in the form of frequent small meals. In some dogs occasional regurgitation may persist despite surgery, but even in these cases, dogs tend to do much better than if they had not had surgical correction.

For the veterinarian: 

Confirmation of persistent right aortic arch is best obtained with a dorsoventral or ventrodorsal radiographic projection of the thorax, which identifies leftward deviation of the trachea just cranial to the heart base.  Barium esophagrams are virtually never required (see both references, below).

Breeding advice: 

Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening. If any affected offspring are born, breeding of the parents probably should be discontinued, although test breeding and close monitoring of offspring may be considered.
 
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources: 

Buchanan, J.W.  2004.  Tracheal signs and associated vascular anomalies in dogs with persistent right aortic arch.  Journal of Veterinary Internal Medicine; 18 (4): 510-514.
Adin D.B., Adin C.A.  2011.  Vascular ring anomaly.  In Cote E, ed.  Clinical Veterinary Advisor: Dogs and Cats, 2nd edition (St. Louis, MO: Elsevier Mosby) pp. 1160-1162.
 Patterson, D.F.  1996. The genetics of canine congenital heart disease.  ACVIM-Proceedings of the 14th Annual Veterinary Medical Forum: 225-226.

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