SAS is a proven inherited condition; however, a commonly accepted mode of inheritance has not been determined for all breeds. Studies indicate that it is either an autosomal dominant trait with variable penetrance or a polygenic trait; in either case, the mode of inheritance is complex, making it difficult to predict patterns of genetic transmission. By eliminating all SAS affected dogs from the breeding pool, we will have a chance of keeping this disease from spreading within the Bernese population.
There is enough evidence of SAS in Bernese Mountain Dogs to warrant routinely screening our breeding animals for heart problems. The symptoms of SAS can be very subtle and the correct performance of cardiac evaluation by board certified veterinary cardiologist is crucial for determining whether or not a dog is affected. Diagnosis of SAS is almost an art. In spite of available technology, without the proper expertise to evaluate heart function, an affected dog can be called “clear”. (Some cardiologists have recommended that evaluation of breeding animals for SAS be performed at 1, 2, 4, and 6 years of age, due to the late onset of some of the murmurs associated with the defect.
What is SAS?
Subvalvular aortic stenosis, also referred to as subaortic stenosis or SAS, is a common heart defect in dogs, especially Newfoundlands, Golden retrievers, Rottweilers, and German Shepherds.
The heart anatomically is divided into 4 chambers separated by 4 valves. The 4 heart valves ensure that blood only flows in one direction through the heart. The aortic valve separates the main pumping chamber (left ventricle) from the aorta, a large blood vessel that carries blood from the heart to the body. In dogs with SAS, there is added tissue below the aortic valve (hence “subaortic”). This abnormal tissue creates an obstruction (“stenosis” is the scientific term) that the heart has to overcome to pump blood to the body. This stenosis makes the heart work harder than normal. A heart murmur is created by blood being pumped across the stenosis into the aorta.
What happens to dogs with SAS?
SAS comes in many grades of severity. We subdivide them into mild, moderate, and severe. Dogs with mild disease usually lead a normal life without complications. Dogs with severe disease may die suddenly or develop exercise intolerance, fainting, rear limb weakness, or fluid in the lungs (heart failure). Heart failure can cause coughing, rapid breathing, or shortness of breath. The course of dogs with moderate disease is hard to predict. All dogs with SAS are predisposed to heart valve infections (endocarditis).
How do dogs “get” SAS?
SAS is transmitted genetically. This has been studied in the Newfoundland breed; the mode of inheritance in this breed is either autosomal dominant with modifiers or polygenic. Dogs with mild disease do not necessarily produce dogs with only mild disease, i.e. a dog with mild disease may sire a litter with severe disease. This defect develops very soon after birth (at approximately 3 weeks of age), and continues to worsen through maturity.
How is SAS diagnosed?
SAS is suspected based on a combination of physical examination findings including a heart murmur heard over the aortic valve. In dogs with a murmur, definitive diagnosis and assessment of severity requires echocardiography with Doppler. Echocardiography allows visualization of the 4 heart chambers and valves and the anatomy of the subaortic area. Doppler allows estimation of the pressure created in the heart by the obstruction. The degree of pressure elevation correlates with the disease severity. Some dogs with very mild disease are hard to distinguish from normal dogs even with this technology. Radiographs of the heart and an electrocardiogram (ECG) are important in the evaluation of dogs with moderate to severe SAS but are usually normal in dogs with mild disease.
What should be done if my dog has mild disease?
These dogs should not be bred so castration or spaying is recommended. Due to the risk for heart valve infections, prophylactic antibiotics should be prescribed by a veterinarian for any potential bacteria exposure (dentals, skin infections, minor cuts or abrasions).
Can a dog with severe disease be treated?
Therapeutic options are limited. Surgery can be performed at some Universities, but it is expensive. Balloon catheter dilation can also be performed at some referral centers. This procedure involves passing a catheter with a balloon on the end down an artery in the neck. The balloon is centered across the stenosis and then inflated to open up the stenosis. This procedure helps to decrease the obstruction in some dogs. Medical therapy may be prescribed to try and decrease the work load of the heart (beta-blockers) or treat signs of heart failure once they develop.
How can I decrease the risk of transmitting this defect?
First, have all breeding animals listened to at maturity by a veterinarian. If no murmur is present, these adults do not have clinical SAS. Second, have all litters listened to carefully. Timing of this exam is tricky; the older the puppy is at the time of examination, the better. Age is important because the defect is progressive early in life such that a murmur will be easier to detect in a
16 week puppy than an 8 week old puppy. Also, young puppies can have innocent murmurs (murmurs not caused by a heart defect). Innocent murmurs go away by 16 weeks of age. Innocent murmurs are difficult to differentiate from mild SAS. We recommend pups be at least 8 weeks old for screening; 12 weeks old is better, and 16 weeks old is ideal. If a pup is to be used for breeding, auscultation should be repeated as a mature adult (over 1 year of age). If pups with SAS are detected, have the sire and dam examined, and do not repeat the breeding.
Are there undetectable carriers of SAS?
Yes. A dog with no murmur may be a carrier of SAS. These dogs are not detectable at this time. Hopefully, future studies will identify a genetic marker that will lead to a rapid, noninvasive blood screening test for this defect and aid us in eliminating this heart breaking problem from so many wonderful breeds.