SAS: An Opposing Viewpoint~~~by Jennifer Walker

In a recent Boxer Underground article, Virginia Zurflieh discussed Aortic Stenosis in Boxers, and the apparently subjective criteria for determining whether a dog is normal, equivocal, or affected. Virginia asked several questions, including:

Has acceptance by board certified cardiologists of a higher aortic flow rate in boxers over the last 8 years led to the production of an increasing number of boxers that are being diagnosed by some cardiologists as "Equivocal"?  Are dogs with flow rates that would not have been graded as clear/normal 8 years ago being bred to one another and producing a percentage of puppies with even higher flow rates? Or with SAS?  In the absence of a fibrous ridge or turbulent blood flow, is SAS merely what an individual cardiologist decides it is...or is there some objective standard that ALL cardiologists adhere to? …. [A]re we asking for trouble by accepting higher flow rates as normal? Or are boxers really "different" from other breeds regarding SAS because they have narrower aortas, and should they therefore be diagnosed and graded differently?  What do you think?

The first few questions are really unanswerable at this time: as far as I’m aware, no one keeps centralized statistics on dogs diagnosed with AS in any year. (OFA statistics are not useful, since most owners of non-normal dogs do not bother submitting the results to OFA.) Nor do we receive any useful feedback from the annual Doppler Echocardiograms performed at ABC each year. We should be requiring that information – we wouldn’t need specific information on the dogs, but if we knew the number of Dopplers performed each year, along with the number passed, number graded equivocal, and number affected, we could track trends in the breed, instead of speculating as we are now. (I will say that when I discussed the status of the breed with Dr. Meurs in 2007, she felt we’d made significant progress in reducing the incidence of AS in the breed since she first began performing Dopplers at ABC.)

So, we don’t really know whether we have more dogs with higher flow rates or not. Dr. Baumwart told me this year that he had 8-10 dogs that did not pass their Dopplers in 2011, out of 160 tested; one of those was severely affected. That puts us at about 6% equivocal or affected, with 0.625% severely affected. Virginia finds that fact worrisome – I find it quite encouraging, considering 10 years ago we were told about 60% of the breed was affected. If Dr. Baumwart was including his "high number of equivocal results" in that, we can speculate that at least 7 of those dogs were equivocal. That brings us to at most 3 affected dogs out of 160 – a 1.875% affected rate that frankly, I don't think you'd avoid no matter what kind of screening you did.

It’s also important to keep in mind that equivocal does not mean affected – it means the results were unclear, and the dog should be tested again. It may well be that nervousness or excitement, hormonal changes, unknown infections or illness, etc, contributed to the issue, and that those dogs will pass easily upon re-evaluation. Research in Scotland showed that Doppler readings can vary by as much as 46.3% from day to day; most variation was less than 20%, but for some cardiologists that can still mean the difference between normal at 1.9 m/sec and equivocal at 2.3 m/sec.

Virginia then asks, “in the absence of physical evidence, is AS simply what each particular cardiologist decides it is?” Based on anecdotes from breeders around the country, the answer is “Yes, it is.” This of course is extremely frustrating, especially when, as in Virginia’s case, a cardiologist changes his criteria for apparently no compelling reason. (The “new” ACVIM guidelines were released to coincide with the formation of the ARCH – the Animal Registry of Certified Health, the ACVIM’s alternative to the OFA. They do not appear to be significantly different from the OFA guidelines, except that the cut-off for normal is 1.9 m/sec rather than 1.7 m/sec.)

What is Aortic Stenosis?

Perhaps this question is the crux of the matter. A high flow rate by itself does not equal aortic stenosis. We may have done ourselves a disservice by trying to simplify the description of the disease: We say that AS is a “narrowing of the aorta” at or below the aortic valve, but we forget to mention that there is a detectable physical abnormality responsible for the narrowing. The Merck Veterinary Manual categorizes AS as an obstruction of the outflow tract, noting that the most common form in dogs is a fibrous ridge of tissue below the aortic valve. The Manual also notes that flow rates are used to determine the severity of the condition, rather than to diagnose it.

This is hardly the first time cardiologists have imposed their own viewpoints about Boxer heart issues on breeders. I still recall the situation with a cardiologist down in Florida who, upon seeing the holter report from a young dog with six single VPCs, diagnosed the dog with FVA (as it was called at the time) and recommended he be neutered. We’ve been told that currently a prominent cardiologist in the East has increased his criteria for passing a dog, and is now "screening out" dogs that he would have graded normal for breeding a few years ago. Apparently, he feels we've made such progress in decreasing the incidence of AS that it's time to raise the standards.

While I’m glad to hear confirmation of the notion that AS is declining in our breed, I’m bothered, if not surprised, by the arrogance of a cardiologist in deciding on his own what the criteria should be for the breed. That is not a decision a cardiologist should be making unilaterally. The American Boxer Club Health & Research Committee has published guidelines for acceptable test results, based on peer-reviewed published research, establishing a system that will remove most affected animals from breeding while keeping the highest number of clear animals. Currently, that guideline is a maximum accepted blood flow velocity of 2.4 m/sec, if there is no evidence of structural abnormalities.

It is fine for a cardiologist to present their personal opinions and cautions to owners of dogs whose flow rate is acceptable per the ABC guidelines. Many owners already prefer a lower flow rate and will not breed a dog with a rate above “their” number, even if the dog is considered normal by the guidelines. The cardiologist should be passing those dogs, however, with a caveat if they wish, until and unless the ABC changes their position. If the guidelines do need to be changed, then cardiologists and breeders should work with the Health & Research Committee to effect that change.

(It's the same as judging, really. How irate would we get if a judge decided an underbite was not a healthy jaw structure, and refused to award wins to Boxers with such a bite? The judge has the responsibilty to judge the dogs according to the standard set by the parent club of the breed, not to impose their own personal opinions and "fail" dogs that are correct per the standard. If the judge feels the standard is unhealthy for the breed, they should take that up with the breed club; if the breed club does not agree, the judge can either judge according to the standard – while, perhaps, explaining to exhibitors how their personal opinion differs – or they should stop judging Boxers altogether.)

Are Boxers Different?

The reason for the higher allowed flow rate in Boxers is that, as Dr. Meurs’ research found, the breed in general has narrower aortas than other breeds of the same size. The study, published in the Journal of the American Veterinary Association (July-August 2006), found that “Indexed LVOT [left ventricular outflow tract] areas in Boxer groups were not different, but were significantly smaller than those of non-Boxer dogs.”

Researchers at Tufts confirmed these findings. Their study, published in the Journal of Veterinary Internal Medicine (July-August 2008), concluded that “Differences in weight-based ERIs [echocardiographic ratio indices], which reflect increased thickness of the left ventricular free wall (LVW) and interventricular septum (IVS) and smaller aortic size, were found in overtly healthy Boxer dogs compared with normal non-Boxer dogs.”

Logically, it makes sense that if the LVOT is smaller, the normal blood flow velocity will be higher, when comparing dogs of the same size. Liquid will flow faster through a smaller opening than it will through a larger one; you can test this theory using an ordinary garden hose and pinching it to decrease the size of the opening through which the water flows.

(I realize that it may seem anomalous to those who know me to hear me supporting Dr. Meurs’ research, given the issues I have with her ARVC-1 genetic test. The two situations are very different, however. The AS study is peer-reviewed, published research and has been duplicated by independent parties. The higher allowed flow rates, in the absence of structural abnormalities, is based on logic and documented fact. The ARVC-1 test, on the other hand, is less defensible. The only peer-reviewed, published research relates to the method of finding the gene, and NOT to the relationship of the gene to ARVC in Boxers. The breeding recommendations contradict logic, remove healthy dogs from breeding, and allow affected dogs to be  bred. By all means, breeders should be performing the test to improve our knowledge of the gene and where it occurs in the breed, but we should not be making breeding decisions based solely on the ARVC-1 test results.)

Looking for Trouble

Sometimes I think we're just looking for ways to eliminate dogs from breeding. I think we are so focused on "perfect" that we're passing over "perfectly acceptable." A soft murmur and increased flow rate in the absence of physiological changes is normal in the Boxer; at least two independent studies have shown this, and other studies show that a significant percent of Boxers have murmurs without the presence of cardiac disease. (In fact, Dr. Baumwart told me that he doesn’t even mention murmurs to owners when he’s doing a Doppler, because in his experience almost every Boxer has one.)

Studies around the world also show that screening for AS (auscultation, with a Doppler if a murmur is detected) has decreased the incidence of the disease in our breed. Cardiologists have noted the same in the US, even with the increased flow rates allowed over the last eight years. According to my personal conversations with cardiologists, both the one I use and those at ABC each year, even among Boxers that are diagnosed with AS we are seeing fewer dogs with severe disease.

We have a system that is working, that is decreasing the overall incidence of disease and minimizing it when it does occur. Yet for whatever reason we cannot take pride in our accomplishments; we cannot use our success to emphasize the value of testing to those breeders not yet doing so. Instead, we must find fault with the system, find ways to undermine its value to the breed, so that rather than encouraging more breeders to screen their dogs, we are dissuading them from doing so since “the test isn’t accurate anyway.” Yes, occasionally a normal dog will screen as affected; occasionally an affected dog will screen as normal. The system is not perfect – these are living, breathing creatures with complex genetic conditions.  Perfection is not likely to be found anywhere...except on paper.

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