Subaortic stenosis, or SAS, is common congenital disease in large breed dogs. SAS a narrowing or stenosis of the area just below the aortic valve, the aorta is the major vessel that takes blood from the heart to the rest of the body. This narrowing causes obstruction or blockage of blood flow out of the heart. The narrowing can be mild, moderate, or severe. if moderate or severe, the obstruction can force the heart to work harder and cause the heart to have to generate a large amount of pressure to get through the narrowing. This causes the heart to remodel and thicken, or hypertrophy. The lesions can begin to show as early as 3 weeks of age and can continue to progress until maturity at 1 to 1 ½ years of age. It is important if a murmur is heard or ausculted in a young puppy, to continue to have it monitored until they are 1 ½ years of age.
If the obstruction is mild, no signs are observed and your pet can live a normal happy life without any treatment. The only caveat is that dogs even in the mild category should receive antibiotics during any surgical procedure (including dental) to prevent infections on the affected heart valve, or infectious endocarditis. In moderate cases, most dogs can exhibit no symptoms while others can exhibit some mild signs. Most dogs with moderate subaortic stenosis may continue to live a normal life span although there is a small risk of developing an enlarged heart and congestive heart failure in the future so continued monitoring is recommended. Severe cases may show no signs while others exhibit more severe symptoms such as weakness, breathing difficulty, exercise intolerance, and even fainting. If the subaortic stenosis is severe, dogs are at a risk of passing away suddenly before 3 years of age. If they live beyond 3 years of age, they must be monitored as they are at high risk of development of congestive heart failure, or fluid in the lungs, in the future.
Treatment is required in some dogs with moderate, and almost all dogs with severe subaortic stenosis. The most common form of treatment is an oral medication called a βeta blocker such as Atenolol. This can decrease the heart’s work, prevent the heart from speeding up, and help to control arrhythmias (abnormal heart beats), to help decrease your pet’s symptoms. In some cases, with severe stenosis and severe clinical signs, a minimally invasive procedure using a special balloon can be performed to help reduce symptoms in dog’s stenosis with some short term success