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Recommendations For The Control of Aortic Stenosis (October 1993)

By Bruce Cattanach Steynmere Boxers

The following points should be noted:

The revised recommendations being proposed are based on a number of veterinary conclusions, some of which have been modified in the light of recent research findings. Further developments are possible. However, it should be stressed that, as initially, the recommendations are liable to err conservatively, this being necessitated by the observed high incidence of dogs with heart murmurs and the need to avoid excessive restraint upon breeding programmes.

Recommended actions are based upon the incidence of normal, rather affected dogs. This warranted by

  • The probable mode of inheritance determined from studies in other breeds.
  • The family studies which are now yielding direct evidence to show that the progeny deriving from the "best" parents are far less at risk of having murmurs associated with aortic stenosis than from others.
  • The high incidence of dogs with heart murmurs
  • The further need to avoid other heart conditions such as pulmonic stenosis and cardiomyopathy
  • The recommendations have three basic objectives:

    To allow breeders to evaluate their own stock and conduct their own family studies with dogs of all ages.

    To provide breeders with a means of breeding away from, or avoiding aortic stenosis and, hopefully other heart conditions.

    To provide research information on heart defects that will ultimately be fed back into the breed.

    Specific Recommendations For Breeders

  • A. In the case of adults i.e. over 12 months of age:
  • All stock should be screened by designated cardiologists.

    Those which are free of heart murmurs (Grade 0) may be considered free of aortic stenosis, and suitable for breeding purposes.

    Those which have only minor (Grade 1) murmurs may, for the moment be accepted as normal and therefore suitable for breeding purposes.

    Stock with Grade 2 murmurs may be re-screened (up to three times)

  • Those which on any re-screening obtain a Grade 1 score, or even found to be murmur free, may be considered suitable for breeding.
  • Those which are consistently found to have Grade 2 or louder murmurs should normally be discarded for breeding purposes, unless in the case of bitches there is no alternative other than to disband the whole of a kennels breeding stock. When
  • Selected bitches should be mated only to stud dogs that are considered to be normal (as described above), preferably murmur free.
  • At most only one or two litters should be taken with the objective of breeding a murmur free replacement.
  • In the case of dogs with murmurs consistently no louder than Grade 2, Doppler echocardiography may be a further option. Those with blood velocities below 2.0 m/s may, for the present be considered suitable for breeding. Other useful Grade 2 dogs might, for the present be available for stud to a strictly limited number of bitches. These bitches should be murmur free or have at the most only Grade 1 murmurs. Dogs with Grade 3 or louder should never be considered for breeding purposes, even if they have a blood velocities below 2.0 m/s.

    Bitch owners are strongly advised to use only tested and proven normal dogs at stud.

    Dog owners are advised to offer only tested and proven normal dogs for stud purposes and ensure, before accepting bitches for service, that their owners are complying with recommended control procedure. At owners risk, stud services could be provided for untested, non-show bitches both of whose parents are murmur free or having Grade 1 murmurs.

    Stock incidentally identified as having heart abnormalities other than aortic stenosis, e.g. cardiomyopathy or pulmonic stenosis, should not be considered for breeding purposes.

  • B. In the case of young stock i.e. under 12 months of age: Puppies aged 6 – 12 months can usefully be tested in the same manner as adults but the results must be interpreted with discretion. Because aortic stenosis develops progressively it cannot be assumed that those that are free of murmurs or have Grade 1 murmurs will be found to be so as adults; there prospects may nevertheless be considered relatively good. On the other, those found to have Grade 2 or louder murmurs are unlikely to become suitable prospects for breeding purposes, and may be at risk of developing the clinical effects of aortic stenosis in later life. The testing of puppies is strongly recommended. Their retesting as adults is essential, however.
  • Additional Information

    To aid breeders implement the recommended breeding control procedures, a list of dogs which are murmur free (Grade 0) or have only minor murmurs (Grade 1) is continually being collated and updated. Copies are available form the Breed Council secretary or secretaries of breed clubs.

    Most breed clubs hold heart-testing clinics with designated cardiologists in attendance at one of their shows each year. Private testing can be obtained by referral through owner’s vets. A list of designated cardiologists may be obtained from the Breed Council secretary or breed club secretaries or heart delegates.

    Cardiologists may advocate ultrasound scanning and Doppler echocardiography for dogs with Grade 3 or louder murmurs as means of evaluating the severity of the condition, i.e. for purely veterinary reasons.

    Baby puppies aged 8 – 12 weeks commonly have minor "flow" murmurs, which usually disappear by about 16 weeks. These are not known to be associated with heart disease in the adult. However, puppies with loud, harsh murmurs should be referred through one’s vet to cardiologists for evaluation.

    Supplementary Notes

    It is strongly recommended that prior to importing stock for breeding purposes, purchasers should ensure that prospective imports are suitably heart tested by qualified cardiologists to ensure they are free of heart defects.

    All breeding stock prior to export abroad should similarly be heart tested and established as normal. In the case of young stock (under one year of age) only those which are free of heart murmurs and have murmur-free or Grade 1 parents should be considered eligible for export, except with the express agreement with purchasers.

    SAS Testing: Auscultation versus Doppler

    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.

    Auscultation versus Doppler - This subject seems to go round and round. I understand that the following would be more 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 a 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 loop holes in the above basic principle.

    Beyond this, there are the 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 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 word’s, 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 effect, 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 as has been pointed out elsewhere auscultation is far more effective for a national control scheme and for single kennels testing numbers of dogs over the years.

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

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

    And then of course, there is probably more variation with Doppler scoring than auscultation.

    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 is at the level of velocity currently defined as normal. In the UK the "pass" rate has clearly been set too high at 2.0 m/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 cardiologists 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 quantitative 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 or 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, and velocity? I am pleading with breeders to retest some of there 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 Newfoundland’s, 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.

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