There’s been a lot of controversy and confusion about SAS (sub-aortic stenosis) in the Boxer community lately, due to the fact that different cardiologists assign different ratings – Clear, Equivocal, Affected – to the same aortic velocity (the speed of blood flow across the aortic valve), depending on whether or not they agree with Dr Kate Meurs that Boxers are “different” from other breeds and therefore can be graded differently – less stringently – than other breeds.
In a summary of the 2003 ABC Health Seminar in the old Boxer Underground zine (http://www.boxerunderground.com/bu2000/abc2003/health_seminars.htm), we reported that on the basis of a study she did in 2002, Dr Meurs concluded that Boxers have narrower aortas than other dog breeds and that therefore a higher aortic velocity – up to 2.5 m/s – can be acceptable in the absence of any other sign of SAS, such as a fibrous ridge or turbulent blood flow. So 2.2 m/s can be one cardiologist’s Clear…and another’s Equivocal. That being the case, it’s only natural for the owner of a Boxer that was rated Equivocal with a 2.2 to want a redo with a cardiologist who has a more liberal interpretation of Clear.
My own experience was a bit different. My dog was echoed at 14 mos at the 2011 ABC with an aortic velocity (flow rate) of 2.21 m/s, and was rated Clear by the cardiologist who did the heart clinic there. He told me that his “personal cutoff” between Clear and Equivocal was 2.25 m/s. However, because the cardiologist who has seen my dogs for years grades murmurs and flow rates according to the standards set forth by the ACVIM (American College of Veterinary Internal Medicine), whose guideline for Equivocal is a flow rate of 1.9 to 2.4 m/s, even in the absence of any other sign of SAS, that 2.21 m/s did NOT make me a happy camper, regardless of the fact that the cardiologist wrote “Clear” on the OFA report. My Boxer’s breeder, whose cardiologist grades pretty much as mine does, was worried, too. So we decided to have the dog tested again at closer to two years of age.
As luck would have it, my cardiologist offered a low-cost echo clinic at a show we attended recently, shortly before my dog’s second birthday. Since I had once had another of my Boxers test with a higher flow rate every time she was echoed until at 2 ½ years old she was ultimately diagnosed with a turbulent flow of 2.45 m/s and mild SAS, I’m not exaggerating when I say my heart was in my mouth as we entered the motor home in which the echo clinic was held. So you can imagine my relief – nay, elation – when my boxer echoed with only a low grade murmur and a flow rate of 1.7 m/s!
Naturally, I asked Dr “C” (“Dr Cardiologist” J) what might have caused the earlier higher flow rate. He explained, as Dr Meurs has, that excitement and stress can have a big impact on flow rate in a young dog. My dog had never seemed particularly excitable, but I can certainly see where being hooked up to a strange machine in unfamiliar surroundings might have been pretty stressful for any young dog on his/her first trip away from home.
After the exam, as Dr C was filling out the paperwork needed to register my dog with the OFA, I took advantage of having him all to myself for a few moments to “interview” him on the subject of SAS in Boxers:
First, knowing that he had a great deal of admiration for Dr Meurs, I asked him why he chose to grade Boxers on the basis of the ACVIM guidelines, rather than the guidelines she had developed for Boxers based on her study. He replied that the ACVIM guidelines were the result of a consensus of a group of different cardiologists, not just the opinion of one person.
Next I asked what the difference was between, say, a flow rate of 1.7 m/s and 1.9. His response was that while everyone agreed that a 1.2 m/s flow rate was good and everyone agreed that a flow rate of 3.0 m/s was not, no one could tell you for sure the meaning of the middle range of velocities, even in the absence of any other sign of SAS. “No one,” he repeated, “we just don’t know.”
Next, I asked Dr C about SAS vis a vis the Boxer breed. His answer surprised me: he said, “Virginia, you know I see a lot of Boxers in my practice and at these clinics; and I rarely see a Boxer with a flow rate above 2.0 m/s. Based on my experience with your breed, I believe there are plenty of Boxers with a lower aortic velocity, without your having to use the dogs with a higher velocity to avoid restricting your gene pool. No other breed of dog has high flow rates like that, including mixed breeds. No other breed.”
So after bending my cardiologist’s ear for nearly half an hour, what did I take away from our conversation? Just this: With 52 ABC members living within the borders of the state,
Florida is second only to (71 ABC members) in terms of ABC membership. There are also four active ABC member clubs in California . There are a lot of Boxers in Florida and my cardiologist does see a lot of those dogs. I’m still not sure what I believe about whether Boxers are “different” from all other breeds because they have narrower aortas, but I do believe my cardiologist when he tells me that he rarely sees a Boxer with a flow rate above 2.0 m/s. And I do believe the cardiologists (all of them?) who believe that the lower the flow rate, the better. So in my own breeding program, I’m going to strive to keep the flow rates of my Boxers below 2.0 m/s. Florida
Unfortunately, this seems to be another example of the lack of black and white information about Boxer heart disease; and another reason for us to try to get comfortable with using our own best judgment along with the opinions of the professionals when making decisions about our own breeding programs.
Next up on the BU Blog: “How Many VPCs Are Too Many VPCs?” Please tune in next week.