Causes of Aortic Stenosis
Aortic stenosis can be caused by a number of things. It can result from some defect or malformation of a heart valve (valvular aortic stenosis), by an obstruction in that part of the aorta known as the ascending aorta (supravalvular aortic stenosis), or by an obstruction in the outflow path of blood leaving the left ventricle through the descending aorta (subvalvular aortic stenosis). Supravalvular aortic stenosis is the most common form of this condition in domestic cats; subvalvular aortic stenosis is the most common type in domestic dogs. What actually causes these various physical defects in the heart can vary. Many times, aortic stenosis is congenital, which means that it is present at birth but is not necessarily genetic in origin. However, most authorities believe that subvalvular aortic stenosis – also called subaortic stenosis or “SAS”, does have a strong hereditary component in almost all cases. Genetic SAS has been soundly documented in the Newfoundland breed. There is no known genetic sex linkage to this disorder, which means that, without other evidence, it cannot be specifically attributed to the father or the mother of affected puppies. SAS is occasionally caused by a bacterial infection of the aorta and/or the left atrioventricular (AV) valve. This condition is called endocarditis.
Congenital SAS in dogs typically involves an obstruction in the outflow of blood from the left ventricle into the descending aorta as a result of abnormal fibrous tissue or some other malformation in or near the area of the left atrioventricular valve. The left AV valve is the doorway between the left ventricular heart chamber and the aorta. It is also referred to as the bicuspid valve or the mitral valve. According to some reports, the name “mitral” valve was coined in reference to the hats worn by Catholic bishops, called “miters.” Apparently, someone thought that the left AV valve resembled those hats in shape and appearance, leading to the designation “mitral valve.”
When the outflow of blood from the left ventricle into the aorta is compromised, that chamber has a volume overload of blood. The heart must contract with more force than normal in order to maintain acceptable forward blood flow and blood pressure. This extra work causes the walls of the left ventricle to thicken (hypertrophy) over time. It also causes a number of other detrimental physiological changes.
Prevention of Aortic Stenosis
Because SAS is thought to be a genetic condition, the sire and dam of a litter that has one or more affected animals probably should not be used as part of a responsible breeding program. Certainly, dogs with clinical SAS should not be bred. SAS due to bacterial endocarditis may be prevented by careful use of antibiotics before, during and/or after procedures such as dental cleanings and surgeries. Otherwise, there is no known way to prevent a dog from developing subaortic stenosis.
SAS is almost always considered to be a hereditary disease, or at least to have a strong genetic component.