SUBVALVULAR AORTIC STENOSIS (S.A.S.)
S.A.S. refers to Subvalvular Aortic Stenosis, one of the more common heart malformations in dogs. In a mild form, there are a few nodes just under the aorta, barely affecting the flow of blood, and the quality of life for the dog remains optimistic. In a severe form there is a fibrous wreath surrounding the vessel partially blocking the flow of blood. This causes undo stress on the heart pushing the blood through a narrower opening, and on the constricted blood vessel itself. Dogs will experience chronic fatigue and at it's most extreme, sudden death.
It is genetically inherited although it's difficult to test for. There are no blood or DNA tests to easily identify it. Carriers are discovered as they grow and begin to manifest symptoms. Unlike most genetic problems, it is at times undetectable by any known means until the pup is several weeks old.
In genetic terms the mode of inheritance is complex and much is still not understood. In Newfoundland dogs it is being studied as an autosomal dominant trait with variable expressivity or as a polygenic trait. It means that only one parent has to have it, and all of their offspring have a possibility of being affected to various degrees. A recent study using Golden Retrievers and Newfoundlands, has suggested that it is inherited as a dominant gene with incomplete penetrance and variable expression. This means that a percentage of the pups will be affected to various degrees.
One of the first ways to detect a problem is to have a Vet screen the heart, listening for a heart murmur, associated to heart problems. If there is no murmur detected by 6-8 weeks old, the pup is considered free of heart problems. If a murmur is present, then the pup should be examined more extensively. Pups with moderate to severe S.A.S. can be diagnosed as young as 6-8 weeks. Depending on the severity, the overt symptoms will be exercise intolerance, fainting, heart failure or sudden death. S.A.S. is a progressive disease. The heart has to work harder and it's muscle, the wall of the heart, gets thicker over time which causes more problems with it's ability to beat regularly and to pump blood. It will cause them to become fatigued easily and perhaps faint. When the heart muscle is very thick the heart rhythm becomes very irregular, cardiac arrhythmia, and the heart can stop.
A pup can have an `innocent heart murmur', which means the pup will have a mild murmur until about 12-14 weeks old and then it will disappear. Afterwards, they also can be considered clear of heart problems and fit to breed, unless there is a family history of S.A.S. If the murmur continues beyond 14 weeks it is advised that more extensive testing is done - echocardiography or cardiac catheterization and angiocardiography. Murmurs can occur without any heart ailment, although it is advised that these dogs not be used as breeding dogs. As well, there is a small percentage of S.A.S. carriers who go undetected as they have no murmur.
The Orthopedic Foundation for Animals (OFA), will register and catagorize dogs as;
1) Normal - congenital heart disease not evident,
2) Equivocal - congenital heart disease cannot be diagnosed nor excluded
3) Abnormal - examination indicative of congenital heart disease.
One difficulty in diagnosing SAS is that the heart murmur heard with SAS and the heart murmur heard in athletic and excited dogs (physiologic murmurs) are very similar. A dog with a predisposition to be athletic, will have an increased heart rate when not in good physical condition. So dogs with these athletic murmurs can actually be better performers and more desireable as breeding dogs. The examiner must have a great deal of expertise in order to discern the difference between these two types of murmurs.
Blue Sterling, B.A.,
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* illustration courtesy of Mostly Medical Clipart
The information contained on this site is in no way intended to replace that of proper veterinary advice, diagnosis or treatment.
It is meant to provide resource, so that we can better understand canine health related issues.