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BOXER AORTIC STENOSIS...continued

Postscript to the Presentation for the American Boxer Club - 2001
Courtesy of Boxer Underground


by
DR. BRUCE M CATTANACH




I have just returned from a trip to find a mass of e-mail writings on my ABC heart talk. The volume has dropped sharply in recent days, and I hesitate to bring up the subject again, especially as my points all seem to have been recognised and some level of agreement reached. But several pertinent questions were asked and require answers and certain other issues perhaps should be emphasised again. So let me try and deal with these -- in sequence:

Ques. 1. Has the severity of cases referred to vet schools changed since the breeding control scheme was introduced?

Ans. - Only severe cases are ever referred to vet schools.

Ques. 2. Has there been any change among the vets at vet schools in the UK?

Ans. - There has been little or no change. In any case, almost all the results come from those selected vets who are experienced with Boxer heart testing.

Ques. 3. Has there been any change in Boxer lifespan since the inception of the control scheme?

Ans. - We have no information at all on that point. This needs an epidemiological study.

Ques. 4. What pathology data exist?

Ans. - The information available is very limited. The problem is that British Boxer breeders are reluctant to have hearts sent for pathology when their dogs die, despite the availability of forms tha can arrange matters in advance of death (see the UK Heart web site). The drive (such as it is) has been focussed on checking what, if any, AS there is to be found in dogs which had been tested earlier and shown to have murmurs of different grades, notably the minor murmurs. My own dog, as shown in the last photo at ABC, had a Grade 1 murmur and a 1.7m/s Doppler velocity and was found to have minor changes consistent with AS at death from other causes (about 10 or 11). There have been others. So some Grade 1 dogs do have AS detectable on pathology.

Ques. 5. How many dogs were involved in the breeding study?

Ans. - About 2000 dogs contributed to the data. Most parents were Grade 1s and 2s, with a good number of Grade 0s and far fewer Grade 3s and 4s. Since data are approaching a point where they will be submitted for publication, I am reluctant to make every aspect public knowledge in advance.

Ques. 6. Low grade murmurs have been found without Doppler evidence of obstruction and vice versa. Does this not call into question the validity of scoring heart murmurs?

Ans. - Exceptions must always be expected. For example, a badly affected heart may be too weak to pump blood hard enough to cause a murmur, even through there is a narrowing of the aorta (stenosis). And the opposite is also true. Large hearts in fit dogs such as the racing greyhounds can pump blood rapidly and with few beats, and this results in spurious murmurs. Neither situation is expected with Boxers presented for examination at shows.

Ques. 7. Isnít Doppler the best test system?

Ans. - Vets are understandably eager to say whether an individual dog is affected/clear, just as the owner is anxious to know. But from the breeder/genetics point of view one wants to know the broader picture for the majority of dogs. We need on average to identify the best. We do not need an absolutely perfect answer. All we need is a guide to which dogs are the best such that we have an opportunity for selective breeding. This is almost like selective breeding for show purposes. We don't ask judges to say what is perfect and then only breed from the perfect specimens. We don't even ask for the very best, the champions say. We all try to breed better from what we have, and with AS, the UK concept is to provide the estimation, or the assessment of the most normal. And, recognising that the scoring is never precise, we have flexibility built into the breeding recommendations so that there are no absolute dividng lines. The breeding control scheme provides recommendations that people can follow with whatever breeding stock they have got.

Ques. 8. Is there really a correlation between loudness of murmurs and degree of obstruction?

Ans. - Auscultation and Doppler measure somewhat different things. Auscultation measures physical abnormality and Doppler measures function. There should still be a relationship between the two scores, and I have the data to illustrate this point. The problem is that the relationship only holds true at higher grades. At the lower end, where velocities are normally somewhat variable, the Doppler scoring becomes meaningless. Murmurs are found further down the scale where Doppler is not sensitive enough to distinguish from normal. Maybe auscultation can confuse AS with PS (pulmonic stenosis), but then we donít want PS either. Mis-diagnosis (PS for AS) is not a problem for breeders, but would be for genetic studies.

So, let's say it again -- auscultation is more sensitive, cheaper, more easily attained, more readily repeated than Doppler. That it is variable is no special disadvantage, as Doppler is variable too.

Ques. 9. Must not the gold standard for AS be based on pathology?

Ans. - This is certainly true, but the old Newfoundland work, plus that of other researchers, established that all test systems relate to the pathological changes. Otherwise none would be used.

Just an add on: A big difficulty as I tried to point out is that the same words are used to mean slightly different things. Is AS strictly only a narrowing, an obstruction, associated with an increased blood flow through the aorta; or is it also the lumps and bumps, the roughening of the aorta walls that do not restrict blood flow but are manifestations of AS nontheless?

The cardiologists in the UK have recognised all to be the same thing. For me as a geneticist with a very different view from the vets, based on many studies with mouse mutants, this is exactly what I would expect -- a range of effects (irrespective of the exact mode of inheritance); and every single reader will recognise this themselves with everyday Boxer breeding.

Take brindle/fawn; there is a range of brindle effect from near fawn (let's call this grade 1) through to reverse brindle (let's call it grade 6). We can all see this by looking, but if we could not do this directly but had to try and work out what was brindle and what was fawn from hair samples ( like the cardiologists working with ausculation, Doppler, 2D ultrasound, etc), we might conclude that lots of black hair means strong brindle, lesser amounts of black hair probably means brindle, but what about the least amount of black hair?? Some might conclude that such a dog is a light brindle. Others might conclude it is fawn. But there is black hair in the coat of fawns so the exact "diagnosis" is not clear. There is all sorts of scope for argument with an imprecise scoring system.

What the UK system specifies is that we don't want the bad hearts (= reverse brindles) and we will encourage breeding from the best dogs, be they absolutely normal (= fawn) or grade 1s (= the lightest brindles). We all know that some lines tend to be dark brindles and others light brindles. We therefore can select for whatever we want. This applies to AS too.

So, as the astute will have noticed, I presented the UK scheme, its rationale, its problems, etc., so that you in America, should you wish to do anything about AS, will see what we have tried to do, what has gone wrong, what we have had to do to fix things, and in total, avoid all the pitfalls that we met. The concept and types of problems apply to BCM as well.You don't at all have to follow the same route, but standardising the diagnosis across the country is one essential need, and setting up an agreed written protocol or guidelines for breeding, with flexibilty to meet different situations, is another. This applies, as far as I am concerned, across the whole spectrum of dog abnormalities, not just with regard to hearts.

About your dog: The selective breeding is the key -- a fair system that everyone can use. You don't want to continue testing for the rest of time, do you? One might say that this is the case for PRA. PRA testing has been going on for 30 years or more.





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