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Editor’s note: The following is a collage of Dr. Bruce Cattanach’s posts
to the Showboxer-L on the subject of the UK Boxer Heart Control Scheme for
Aortic Stenosis, the advantages of auscultation over Doppler for a large-scale,
national SAS control program, and the implications of the UK Heart Control
Scheme on North American efforts to eradicate BCM/FVA.
By Dr. Bruce Cattanach
PART I It seems to be the silly season again, when attempts are made to minimize the achievements of the UK heart scheme and to deride the principles involved. I hope that I have never indicated that the testing system is flawless. It is anything but. It has flaws but auscultation does provide a practical method to allow breeders to do their best among all their dogs (rather than just some) and across the whole breed (rather than just some breeders). There are far fewer limiting factors such as costs, availability, etc. than with other systems. It allows breeders basis for selective breeding against SAS on a wide scale, across the whole country and to an extent even internationally. One cannot make this auscultation perfect. Dogs' scores do vary and not just between testing by one cardiologist or another. They can vary while testing is in progress. Produce a squeaky toy, and any murmur is liable to become louder as the heart rate goes up and the adrenalin kicks in. And then, are all murmurs significant? No. The fit racing greyhound has a large powerful heart that beats slowly but courses larger than "normal" volumes of blood through the aorta on each beat. This causes turbulence and a murmur is heard. And, does the absence of a murmur mean normal? No. A seriously affected heart may function so poorly that it can't move blood fast enough to cause a murmur. How far either of these extremes has relevance for the show Boxer I don't know, but at least these situations provide some idea of the complexity of scoring. But this leads on to the whole issue of how stringent the testing should be. Because of the high incidence of UK Boxers with murmurs, every way possible has been tried to allow more dogs to "pass." Two or three attempts are allowed and the best result is used. This is warranted for the above reason, but probably serves us badly. A dog with a final score of Grade 1 may in fact really be a Grade 2, or worse. But one hopes that at least some of the dogs that have tested Grade 2 once and then obtain a Grade 1 later will be among the "best" of this category. We try to pick the best from what we have. However, I have seen how some breeders have "gone by the book" as far as the control scheme guidelines are concerned only to land in trouble. This built-in flaw can usually be seen as the probable cause. Then there is Doppler. This too can mislead as currently applied. The pass rate of under 2.00m/s is by all standards everywhere far too lenient. But we need passes. And, again, I'm afraid that some people have come a cropper by relying on a Doppler pass when auscultation has indicated danger. But what other way is there of dealing with the high incidence of affected dogs? To worsen things, the auscultation scoring in the UK has become extraordinarily tough. The cardiologists know it and readily admit it. But this is a disaster for breeders and a disaster for any genetic analysis. The goalposts keep moving and everyone tends to lose heart. So tough scoring is now a negative for practical purposes. At another level however I now begin to doubt that there are any Boxers with "normal" hearts, if one looks hard enough. Here I have asked breeders and clubs if they would be willing to push this further and for experimental reasons only investigate if any Boxers, if rigorously tested (using all test systems), could remain murmur free and otherwise SAS free. And then if some were found, how would they breed? I'm afraid the response has been less than enthusiastic. So, all one can do is to try and interpret as validly as possible the collated fragments of information that come in from random heart testing. But has it worked? You bet it has. Despite the nit-picking, from me as well as others who are not involved, the cardiologists insist that in the UK, SAS is no longer a major Boxer problem. They know the referral system and how it works, but they all state the same conclusion. So why should I argue? Beyond this of course, it should be remembered that the whole attack on SAS was prompted by the deaths of significant dogs within the breed, champions and the like. Do we have any deaths among our top show dogs nowadays? I don't know of any at all, and I know the breed quite well. For me however, the important finding has been that dogs with the least effect by auscultation produce, on average, progeny with the least effect – despite all the scoring problems. So a response to selective breeding must be expected, although, of course, for breed improvement, there has to be selective breeding. Progress with SAS is now entirely up to breeders. Let me close with a shot at the Doppler test that some think offers the best objective measure. It seems to me from a recent description by one of our cardiologists to be rather like shooting ducks in a fairground stall (my wording). One has to try to get a measure while viewing along a length of the aorta and this ideally should be down the centre of the "tube" where the flow is unimpeded and the fastest. Close to the walls, the flow is reduced. So, there is potential for a nice wobble here. Add to this that the "tube" (the heart) is swaying about as it beats and it seems a pretty difficult job to get a consistent value. This of course is why we work upon at least 10 readings. One would imagine the worst readings would be the most meaningful (where one is hitting the target), but I think the average is usually used. A good rationale? I am not exactly convinced, but then I am not a Doppler fan, for control scheme use anyway. Whatever, we are trying, and at a national rather than just single breeder level. And despite all the problems, the scheme and its rationale are good enough. PART II To return to the start of the UK scheme: In brief, it had been noted in the late 80s that there was a large number of young Boxers dying from heart associated causes. This became harder and harder to ignore to the point that action was finally taken. This constituted a survey at the British Boxer Club’s championship show in 1990, when two cardiologists from Edinburgh screened about 120 dogs and found a high incidence of murmurs consistent with SAS. They further indicated that the disease was known to be a Boxer problem, both from the vet literature and from the Edinburgh experience, which showed that almost half the referred cases of SAS in dogs were Boxers. On this basis action was initiated, but it was probably only the appearance of clinical effects, and even deaths among known show stock, that spurred serious action against the disease. With Edinburgh cardiologists’ advice, a control scheme of recommended breeding procedures (see UK Heart Testing Web Site) was initiated for all to use in combination with a list of all dogs that had been tested and passed as normal. This has allowed everyone to do their best to selectively breed away from the disease and it appears to have worked/be working. As indicated in the previous post, all of the UK heart centers and vet schools report almost negligible numbers of referred cases these days, and we have no well-known show dogs with serious heart problems anymore. This is not to say that all is perfect or even acceptable, but I think an improvement in the health status of the breed in the UK can be claimed. PART III It would be useful to know more about the disease and how widespread it is in tbe breed at all levels of effect. Analysis of the breeding data show that the murmurs have a genetic basis and that it is possible to breed for lower grade murmurs, but it would be useful to better understand the genetic basis of these heart murmurs, i.e., the inheritance. With this information we might be able to see how best to go in the future even to finding the gene/s responsible. But this would require research, rather than just routine testing and analysis of combined breeding results. The UK cardiologists have shown great interest in participating in any such research project, there has even been Kennel Club interest, but there seems little breed enthusiasm. I guess people are satisfied enough with the testing system we have and its results. Breeding control has to match the magnitude of the problem. If you have only 20% of your dogs free of murmurs, there is no point in recommending that only these be used for breeding. Extend this up the scale. Where does one draw the line? Surely the line should be set where a large enough proportion of the breed can be included in the "suitable for breeding" category. They may not all be perfect but at least they have been assessed as the best; and as long as recommendations are offered, rather than absolute rules, there is scope for some flexibility and breeders can do their best. In effect, where I finish up is essentially in agreement with the quoted base-line US cardiologist view: The best one can do is to weed out the worst. There is no absolute, perfect test and, if there were such a test, one could probably not apply it rigorously in practice anyway. I look forward to hearing what is decided about heart testing [for BCM/FVA] in the States. |
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