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SAS
Sub-Aortic Stenosis (SAS) What is SAS? Sub-Aortic stenosis is a common congenital (present at birth) defect, found most often in large dog breeds. This condition is an abnormal narrowing of the juncture between the left ventricle of the heart and the aorta. The narrowing is usually the result of a scar like tissue which has formed a ring just below the aortic valve. Diagnosis of SAS in its mildest, or sub-clinical, form, is extremely difficult. Due to the wide range of possible stenosis (narrowing) ranging from minor to severe, the impact upon the dogs overall health and symptoms will also present a wide range of possibilities. A dog affected with the mildest form of SAS will lead a full life of normal duration and quality, and will most likely be completely asymptomatic. Even those with moderate SAS can lead normal lives. However, dogs that are severely affected are at risk of sudden death. Heart failure is very rare except in the most severe cases, and those dogs usually have a severe mitral valve insufficiency as well as SAS. Diagnosing SAS The first examination is the auscultation, or exam with a stethoscope. This is performed to detect any murmur, however it is extremely difficult to hear the murmur in the mild cases and it requires a trained ear, it can not be expected that a vet without experience in this particular examination will detect a mild murmur. Electrocardiograms are often normal, regardless of the degree of disease. In the most severe cases, radiographs can possibly show some ventricular enlargement, but they often appear normal as well. A Doppler echocardiogram will show the presence of subvalvular lesions, and an increased velocity in the flow of blood across the aortic valve due to the constriction of the valve by the lesion. Normal velocity is determined at 1-2 meter/second, in severe cases of SAS the velocity can be up to 5-8 meter/second. A Doppler will also show aortic regurgitation in a high percentage of SAS cases. What happens inside the affected heart? The heart is the organ (or system) which frequently fails in the dog and surprisingly, it happens to dogs of all ages. In the young, this is typically the result of congenital abnormalities in the formation of the heart or blood vessels, which surround it. In older animals, it is usually a case in which one side or chamber is weakened or over-worked due to altered circulatory patterns. The heart is actually nothing more than a mechanical pump. It accepts blood on one side and forces it through the lungs, then its other half pumps the liquid on through the entire body. The heart does not change or alter the blood in any way. It has no glandular tissue and therefore secretes nothing into the blood nor does it extract anything. It is probably the simplest and most easily understood organ in the entire body. As a quick review, blood returns from the body and enters the right upper chamber of the heart, called the right atria. At this point, the blood is low in oxygen but high in carbon dioxide. It is then pumped from the atria through the right atrioventricular valve into the right ventricle. From this larger chamber, it is then forced on into the lung field through the pulmonary artery. This is the only artery in the body that carries non-oxygenated blood. Carbon dioxide is a by-product of body metabolism and is attached to the red blood cells. In the lungs, carbon dioxide is replaced with oxygen. The reoxygenated blood then moves through the pulmonary vein back into the heart and enters the left atrium. This chamber pumps the blood through the mitral valve into the left ventricle, which is the largest, most heavily-muscled chamber of the heart. While other chambers only move the blood a short distance, the left ventricle has the responsibility of forcing blood throughout the entire body. This completes the system, which allows blood to circulate throughout the body and then return to the heart.
In young dogs, a congenital condition referred to as aortic stenosis affects the left side of the heart. When the left ventricle pumps blood to the body, it goes first through the aorta. This huge artery then branches into smaller ones that supply different areas. With aortic stenosis, the opening between the left ventricle and aorta is smaller than normal, the narrowing is usually the result of a scar like tissue which has formed a ring just below the aortic valve and can range from very mild to very severe. The narrowing causes the blood to flow into the aorta under higher pressure (like putting your thumb over the end of a garden hose). This makes the left ventricle work harder against the pressure and the heart muscle thickens. Animals with this disorder are weak, lethargic, prone to fainting and may have poor growth rates. All of these signs are due to inadequate profusion of the tissues with nutrient and oxygen-rich blood. These animals typically have much shortened life spans and death finally results from left-sided heart failure. Even though the left ventricle is extra strong, it cannot maintain this workload over time. >Heritability SAS is an inherited disease. That much has been determined. However, the exact mode of inheritance still has not been proven. At present, there is widespread opinion that the disease is a dominant gene trait with 'imperfect' or 'variable' penetrance. It is also believed to be polygenic. These factors make the exact mode of inheritance extremely complex, and the struggle to eliminate carriers from a breeding program is a difficult and elusive endeavor. In simple terms, any affected dog can produce SAS in its offspring; there does not need to be a matching gene in the other parent. A clinically unaffected dog may produce SAS in its offspring if it carries the gene. There is evidence, but no proof, to suggest that the more severe the genetic defect, the more cumulative the affects of the disease will be. Until there is a definitive DNA test available, there is no way to detect those dogs with extremely mild, sub-clinical disease (except necropsy), nor is there a way to detect those dogs who are completely disease free but still carry the gene for SAS. Sources: www.barkbytes.com by Jennie Bullock clubs.akc.org www.peteducation.com by Marty Smith, DVM www.moonstruckmeadows.com Heart study of the Dogue de Bordeaux in Denmark Heart study of the DdB in Denmark has been initiated by Jørgen Koch, senior lecturer and veterinarian ph.d. at the Royal Veterinary and Agricultural University of Denmark in collaboration with the Danish Dogger Club, after he had seen numerous cases of DdB’s with aortic stenosis within a short period of time. He therefore suspected SAS to be a problem within the breed and in the Fall 2004 the Danish Dogger Club decided to arrange a voluntary examination for those DdB-owners, who wanted their dog examined. All examinations were carried out at the Royal Veterinary and Agricultural University of Denmark by Jørgen Koch himself and veterinarian Miriam Höllmer. The examination diagnosed the dogs on two points: Velocity in the flow of blood across the aortic valve
Results of the study:
Overall the study shows that the DdB has a significant heart problem with an under-dimensioned cardiovascular system. Some of the examined dogs had hearts the size similar to breeds half the size of a DdB. At the moment (Fall 2005) only the above-mentioned 53 dogs have been examined, and the examination has only been carried out once (Fall 2004). Denmark is the first country to initiate a systematic study of aortic stenosis with the DdB. It is therefore not possible based on this slender foundation to establish how and to which extend aortic stenosis is inherited with the DdB. At this point we do not know enough about the disease within our breed, however there is no doubt that the disease is hereditary. There is no breeding restriction on aortic stenosis and no demand to have your dog examined in order to use it for breeding, breeders choose voluntarily whether they want to have their breeding animals examined or not. |
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