Wednesday, July 20, 2011

SAS: Are American Boxers Headed in the Wrong Direction?

Recently, an SB-L member asked the list to comment on a situation in which her dog had been cleared of SAS for an OFA listing by a board certified cardiologist at 16 mos with a flow rate of 1.9 m/s; but had been subsequently diagnosed with SAS at 22 mos by another board certified cardiologist with a Grade 3 murmur and a flow rate of 2.6. 

Prior to that SB-L discussion, a friend and I had been talking about what exactly was an "acceptable" flow rate for boxers, who sets the standards for what's clear of SAS and what's not, and whether acceptance of higher flow rates in boxers by some veterinary cardiologists is leading to an increase in the incidence of SAS...or not. My friend has kept a record of all the echoes she's had done on her dogs over the years, and has noticed that the dogs that might have been cleared of SAS a few years ago with a higher than 2.0 m/s flow rate, are now being graded "Equivocal" (uncertain) by the SAME cardiologist! 

Before we go any further, some background: At the 2003 ABC, Dr Kate Meurs announced that she had just completed a study of SAS in boxers, and had found that boxer aortas were narrower than those in other dog breeds, and that increased flow rate could be caused by 1) stenosis, 2) excitability (especially in young dogs) and 3) pregnancy/heat. I did a summary of Dr Meurs' presentation in the Boxer Underground and wrote:  "[Dr] Meurs' recommendations (based on this study) were that 'a blood velocity of 1.7 to 2.5 can be acceptable IN A BOXER, if there is no turbulence or fibrous ridge/ring detected on a color-flow Doppler echo.'" (The fibrous ridge may or may not be noticeable on Doppler, but it is definitely what is looked for on autopsy to confirm or disprove the presence of SAS.) A velocity of 1.7 m/s was historically chosen as "normal" because "that's what you can hear" – i.e. a blood velocity over 1.7 can be heard with a stethoscope as a murmur.  Again, Dr. Meurs said her study indicated that a blood velocity of 1.7 to 2.5 m/s "can be normal" in a boxer, in the absence of turbulence or a fibrous ridge in the aorta.  Here is a link to the BU article on Dr Meurs' report:

After he learned of Dr Meurs study, our local (Florida) cardiologist became far more lenient than he had been in grading the flow rates of the boxers we brought to him for pre-breeding screening. Now, 8 years after Dr Meurs did her study, my cardiologist has gone back to the "old" standards, because the Ad Hoc Committee of the ACVIM (American College of Veterinary Internal Medicine) has established (re-established??) the following diagnostic guidelines:
·  Manual restraint during echo is preferred (in cases where sedation is required, please record drug and dosage).
·  Maximal LVOT velocity is calculated using Doppler studies from both the subcostal and left apical views using the average value of 3-5 beats.
·  Normal: Dogs with LVOT velocity < 1.9 m/s in the absence of either structural abnormalities of the LVOT or abrupt acceleration within the LVOT.
·  Uncertain: Dogs with LVOT velocity >1.9 and < 2.4 m/s in the absence of structural abnormalities of the LVOT or abrupt acceleration within the LVOT.
·  Affected: Dogs with structural abnormalities of the LVOT or abrupt acceleration within the LVOT or a velocity > 2.4 m/s.
·  Presence or absence of AI can be recorded but is not intended to be a diagnostic criterion for the presence of absence of SAS.
At the ABC this year, a friend had his promising young dog (14 mos) echo'd at the heart clinic there. The ABC cardiologist -- Dr Ryan Baumwart -- cleared the dog of SAS ("Normal") for an OFA listing with a Grade 2 murmur, a flow rate of 2.21 m/s, and "mild aortic regurgitation." He said there was no need for my friend to have his dog echo'd again when it was older. (My own cardiologist won't  clear a dog for OFA certification till it's 18 mos old.) Later at the ABC general membership meeting, the chair of the ABC Health & Research Committee, Dr Joyce Campbell, said that the ABC cardiologist was alarmed by the number of "Equivocal" ("Uncertain") diagnoses he had given out (8-10), and warned the meeting attendees to take greater care in screening their dogs for SAS.

Keeping in mind that the OFA lists a dog as normal, but does NOT list any info on flow rate, grade of murmur, etc, my question regarding all of the foregoing is this: 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?

When I talked to Dr Baumwart after he had examined my own dog, he told me that his "personal" cutoff for Normal was 2.25 m/s. So presumably, the dogs he rated as Equivocal at the ABC had flow rates of 2.25 m/s or higher. And possibly many of the dogs he cleared for an OFA listing as Normal had flow rates of between 1.9 and 2.25 m/s?

So again, are 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?


  1. What I find interesting is all of the dogs above were cleared before 24 months. I thought 24 months was the mimimum age for clearance according to ABC? Perhaps that is one explanation. I have an 8 yo male that was equivocal by Dr Meurs at 24 mos, cleared by her at 36 mos, and at 8 years has the same flow rate, no ridge, and laminar flow, no turbulence. Age can be crucial.

  2. Bill, I agree, but Dr Meurs has recently said (within the last few years, I think, but I'll check) that if the dog is echo'd and cleared at one year of age, there's no need to do another echo. The ABC cardiologist obviously agreed with her, because he told me there was no need for me to do another echo on my own just-over-a year-old dog, and cleared him for an OFA listing at the ABC. My own cardiologist will not sign off on an OFA clearance if the dog is under 18 mos. This whole "my cardiologist versus your cardiologist" situation is making me crazy!

  3. Definitely understand. Kate echoed a bitch of mine last ABC - yes I was the guy who got the only 4 echos that were done in 2010 - and would not clear an 18 month old bitch with a 1.89 flow rate and the note 'normal study'. It will be interesting to see what happens when I get her retested this September!

  4. All of this is super interesting, but I think the majority of my questions revolve around how much we really know about the mode of inheritance of this disease? It seems as if we've had this information for quite a few years, but we've made little progress on figuring out the why's and how's of how it's passed down. Cleared dogs (from cleared lines, with cleared siblings) are still producing affected offspring. How does this happen?

  5. A puppy out of UK bitch here in the States was equivocal as a baby (6 months, I think), equivocal at the 2nd Doppler, then diagnosed as mildly affected and denied breeding clearance on her 3rd by the cardiologist who did her 2nd. Then this week, a month after she turned 2 years old, the cardiologist at Cornell (her 4th Doppler -- can you tell how important this was to her owner, who happens to be a vet, herself?) gave her the green light. No evidence of disease. That's three different board-certified cardiologists, and three different results. What on earth can we make of that?

  6. Jessica, Uk geneticist Dr Bruce Cattanach, who was instrumental in setting up the UK Aortic Stenosis Control Scheme, presented evidence at an ABC health seminar in 2001 to the effect that dogs with lower grade murmurs (0-1) tended to produce offspring with lower grade murmurs, and that thereby reduced the incidence of *clinical* SAS in the UK. We reported on Dr Cattanach's seminar in the Boxer Underground ( IMO, Dr C's seminar is a terrific resource for anyone who's interested in learning more about SAS in boxers.

  7. Thanks, Virginia! I'm speaking, however, of those instances, like the one I mentioned above. Where does that put a boxer breeder in the instance of two cleared parents, no murmurs, reasonably low flow rates and no known affected relatives producing severely affected offspring? How is this possible?

  8. Jessica, read the 2001 BU article to which I posted a link in my first response to you (above). I'm not a scientist, never mind a geneticist, and I don't know the answer to your question; but I think that BU report on Dr Cattanach's ABC seminar ( will provide more information about the inheritance of SAS.

  9. My cardiologiist feels that given two stud dogs that are SAS clear, choose the one with the lower flow rate if possible. Always select for a lower flow rate and boxers will improve. I thinkby allowing higher flow rates we are not doing the breed any favors. Karen Cameron-Howell

  10. Hey guys, where did you find the ACVIM guidelines? Thanks! Anne