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SAS TESTING: Auscultation versus Doppler

I have been away for a couple of weeks but have picked up the end of an argument on auscultation versus Doppler.

The point seems to have been missed, if I am not mistaken, that the two test procedures screen for different things. Auscultation screens for physical changes whereas Doppler screens for changes related to function. There is a relationship between the two, but it is not direct or exact.

Auscultation screens for more than just impaired function. It is the better system especially for mass screening of a breed. But if you want a veterinary diagnosis or prognosis then Doppler is the tool of excellence.

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Auscusltation versus Doppler - this subject seems to go round and round. I understand that the following would be most correct: If a dog is auscultated BY A CARDIOLOGIST WITH GREAT EXPERIENCE IN BOXER HEART TESTING (such as a few selected ones we have in the UK) and this dog is found not to have heart murmur, then it will not be found to have SAS on subsequent Doppler either.

But in practice cardiologists vary, experience even among this specialised group varies, dogs can even vary as they are being tested so that screening has to take more than a few minutes, etc, etc, so there are all kinds of loopholes in the above basic principle.

Beyond this, there are the very few exceptional cases where seemingly murmur-free dogs really have developed both murmurs and stenosis, as determined by Doppler, with age. This exceptional scenario has been found with dogs that uniquely had an abnormality develop within the aortic valve itself, not below (sub-aortic stenosis) as is most commonly found.

So, the bottom line is still - with the necessary level of testing - auscultation still picks up LOWER LEVELS OF THE CONDITION WHICH IN MORE SEVERE FORM CAUSES SAS than Doppler. (It’s all a play on words which gives a mixed message. I think when vets talk about SAS, they are talking about a dog being affected to a level they can recognise by Doppler blood velocities (high). Lower levels of the effct, meaning no actual stenosis (narrowing) but still lumps and bumps which are milder effects, but which do not represent stenosis proper, still cause sound.)

And has been pointed out elsewhere auscultation is far more effective for a national control scheme, and it is far more effective for single kennels testing numbers of dogs over the years.

At all levels auscultation wins - and especially if you want to achieve something.

I would emphasise that the view on ausculatation vs Doppler is not my own personal one, but rather what has been hammered into me over the years by our most experienced cardiologist/s - and to me it does make sense.

And then of course, there is probably more variation with Doppler scoring than with auscultation. But that's another story.

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I find myself in a bit an awkward situation regarding detailed answers here. Obviously I will be dealing with all such problems in my talk at the ABC and even though only a minute number of Boxer owners are liable to be there, it would be a shame just to rephrase what I have written.

However, briefly, auscultation recognises sound, sound is caused by any type of anomaly within the aorta, lumps and bumps (as in the noise of a rocky stream) as well as a more severe effect that causes partial closure and forces the blood to travel faster making a noise (as the end of a hose). So in principle, the auscultation picks up the minor manifestations of AS that do not impair blood flow - it is more sensitive for effects that are the basis of the thickening. It detects abnormality but not necessarily function, and Doppler measures function - by blood velocity.

Doppler "passes" can therefore be achieved in auscultation positive dogs by the fact that there is not a definite narrowing, not increased blood flow, only the turbulence detected by auscultation. So Doppler is not expected to pick up Grade 1s or even many Grade 2s. This at least is at the level of velocity currently defined as normal. In the UK the "pass" rate has clearly been set too high at 2.0m/s.

Beyond this there is liable to be as big or bigger variation in Doppler scoring by different vets than even with auscultation. The quote here is that it took our lead cardiologist 18 months of scoring every day to begin to get consistent results.

The positive for Doppler is that it clearly defines the disease in sufficiently affected dogs - which valve is involved and even perhaps where, within, below, above the valve, and presents a definitive quantiataive diagnosis and prognosis in sufficiently affected dogs. It is the classic tool for this purpose.

Physiological murmurs are often talked about but I am not aware of any dog with a minor murmur that has been found on pathology/autopsy to have a normal AS-free heart. Clearly there are minor murmurs in puppies which are transitory and do not relate to adult conditions. And murmur grade is highly sensitive to external effects like excitement, activity, anything that makes the heart beat faster. Test conditions have to be standard. This is central to current research: are there any Boxers that have absolutely normal hearts, what influences grades, velocity? I am pleading with breeders to retest some of their Grade 0 dogs to see if any always grade as such, but!!! And one would then want to see what the pups heart status is when both parents are absolutely free of murmurs. But, again!!!!

All the above is specific to Boxers please note. In Newfoundlands, for example, with their big barrel chests, then auscultation is not so valuable and Doppler has to be used.

Whatever the arguments, the UK system is working and it has to work on the basis of the breeding data - given appropriate breeder action.

Bruce M Cattanach
MRC Mammalian Genetics Unit
Harwell, Didcot, Oxon OX11 0RD, UK
email: b.cattanach@har.mrc.ac.uk
Tel: 01235 834393 Fax: 01235 824530