Changes in CHIC Cardiac Clearance for German Shorthaired Pointers, 2014*
Every breed has a spectrum of cardiac diseases, some early onset, and some occurring later in life. Why do we cardiac screen German Shorthaired Pointers at a young age?
Veterinary literature and the GSPCA 2005 Health Survey identified subaortic stenosis (SAS) as our breed’s most prominent early onset cardiac problem. It is caused by fibrous tissue which continues to develop after birth, partially blocking the heart’s aortic outflow tract just below the aortic valve and reducing the flow of blood to the dog’s circulatory system. The force needed to push blood through this abnormally narrowed opening damages the heart as it strains to provide the oxygen-rich blood supply the dog needs. In some severe circumstances the damaged heart and the turbulent blood flow set up cardiac arrhythmias causing a dog to literally drop dead. Dogs with severe SAS rarely live beyond age 3 without medication, whereas dogs with very mild SAS may not show any symptoms and lead a normal life. The forced blood flow creates the sound of a heart murmur.
No one knows what causes the cells in the aortic area of a baby puppy’s heart to continue to proliferate after birth --and no one knows what turns it off as the dog reaches maturity. The standard cardiology text Small Animal Cardiology (Kittleson), says “it is… uncertain at what age an observed obstruction can be considered fully formed.” But dogs who reach adulthood without any evidence of SAS will not develop it later in life.
Dogs with any level of SAS should not be bred and littermates should be carefully screened before breeding.The mode of inheritance is unknown in GSPs, but in other breeds it is known that dogs with SAS can produce puppies with severe SAS or no evident SAS at all. Unaffected littermates of dogs with SAS could be silent carriers and their offspring should be carefully screened as well.
The gold standard for diagnosing SAS is a two step process of auscultation (listening to the heart with a cardiac stethoscope) followed by an echocardiogram which measures the speed of blood flow across the aortic valve. However, because almost all cardiac diseases are associated with murmurs, OFA allows clearance after one year of age for all breeds using only the first step of auscultation, during which a veterinarian listens for the location and sound of murmurs. ** Not all murmurs are clinically relevant -- some are innocent murmurs which go away as dogs mature or may be very mild murmurs that will not worsen with age. Shorthairs can also have an athletic heart – heart muscles so strong from exercise that they pump blood faster than what is considered normal in other dogs. Finally, SAS is considered a very difficult disease to diagnose in some situations. The OFA site itself says that at times it may be impossible to distinguish normal from abnormal even with advanced diagnostics.
A 15% sample of cardiac cleared GSPS on the OFA site showed that 14% were cleared by echo including auscultation and 86% used auscultation alone.
Most dogs are cardiac cleared at dog show clinics or other locations where dogs are scheduled at 15 minute intervals and a veterinarian (a cardiologist, a specialist or a practitioner) listens for murmurs and either clears the dog, asks that the dog be brought back for re-evaluation when more mature, or refers the dog for additional testing. Clinic locations are chosen by the host club, and often present less than optimal listening conditions.
So here we have SAS and other possible early onset cardiac diseases***screened using the less precise diagnostic method, conducted by professionals with varying levels of training in a less than optimal listening environment under hurried conditions. Yet breeders hang on the results as if they are absolute, and this is often the only time these disease issues are specifically looked for prior to breeding.
The one size fits all OFA policy of clearance at 12 months is not a good fit for a large, slow maturing breed like GSPs with a predisposition to a disease that may continue to develop beyond 12 months.
The Committee asked how we could improve cardiac screening without discouraging owners from testing. At a clinic an auscultation plus echo costs $150-$200 versus $40- $50 for auscultation alone, so it was felt not realistic at this time to require the more definitive but higher cost test without affecting the number of breeders who would test. Further, because breeders are accustomed to testing only once, it would be difficult to achieve good compliance if we required multiple screens during a dog’s life. We cannot change the environments in which clinics are given or the clinic schedule.
We felt two changes could be made that would be relevant. First, improve the skill level of the veterinarians doing the screening by requiring that it be done by a cardiologist (currently about two thirds of Shorthairs - 68% - are cleared by cardiologists). Second, increase the age at which the screening is done to better differentiate among the types of murmurs in these quick decision situations. Kittleson, in Small Animal Cardiology says breeds prone to SAS should not be cleared until they are “full grown.” By 24 months innocent murmurs have long been resolved so cannot be confused with any still existing murmurs, and the fibrous tissue associated with SAS is more likely to be fully formed so that the severity of the disease can be better evaluated.*** *By avoiding subsequent re-testing, this approach would not cost breeders more than they are currently spending, and would not delay enrollment in CHIC since dogs already have to wait till 24 months for hip and elbow clearance. (Breeders who feel they need earlier cardiac information can still test a dog before 24 months for their own purposes.) These are very modest changes which will help avoid missing important indicators of more serious conditions.
Our goal is also to educate the membership that cardiac clearance is not just a hoop to be jumped through in order to get a CHIC number. Echocardiogram remains the preferred and more definitive method of cardiac screening targeted toward the specific problem known to be prominent in our breed. Although our breed is generally heart-healthy, SAS is not the only serious disease we have. Breeders also still need to be alert for later onset cardiac diseases such as dilated cardiomyopathy (DCM) and degenerative valve disease that may have a hereditary component. And finally it should be noted that early cardiac clearance of breeding stock is even more important for dogs who stress their hearts on a regular basis either through performance events or in the field.
Health and Welfare Committee, 2014
*Material in this paper was drawn from the suggested online readings listed at the end. We thank cardiologist Nancy Morris DVM ACVIM for her helpful comments as we prepared this paper.
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