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: http://www.boxerunderground.com/bu2000/abc2003/health_seminars.htm
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? VZ