Another year has gone by and although from my point of view it has been a "bumpy ride", breeder effort to deal with Boxer aortic stenosis (AS) is proving successful. The number of dogs tested now stands at 3000 and reports from the vet schools are consistently indicating that the incidence of referred heart cases in Boxers is declining. Boxers no longer appear to be at the top of the list of "heart breeds"
The Cardiologists have justifiably been delighted with the perceived improvement and we can indeed, all congratulate ourselves upon this success. But there is another problem. If the incidence of severe cases of AS is on the decline, the incidence of murmur free dogs and those with only minor murmurs should be on the increase. But this does not appear to be true. The reverse would almost appear to be the case and this does not make sense. Fortunately, some answers have come from analysis of the computer database of records.
Several complications have come to light: first, as I have indicated before, the severity of the grading has become much more rigorous since the start of heart testing; second, a variation in scoring among cardiologists was indicated; and third, the grading itself has proved in some cases to be quite variable, even with single cardiologists. It is therefore, hardly that many of us have been disappointed when dogs have not bred as well as might have been expected.
It has amazed me that when the evidence was presented to the cardiologists, rather than being offended by apparent criticism, they have taken it as a challenge to their expertise and attempted to resolve each of the difficulties. Hence, the planned new initiative on heart testing which was described in Boxer '96, and ultimately put into operation this year. Two cardiology testing sessions have been held, the first as Towcester in the spring and the second in Coventry this autumn.
The Towcester findings were based on over 40 dogs, each of which had been graded previously. They included animals that had been given the same scores on different occasions and others which had obtained different scores. Eleven cardiologists were present and each independently graded all the dogs, some of them twice. A significant variation between cardiologists in the severity of their grading was found, confirming the conclusions from the database but it was also established that individual dogs could also vary when scored while individual cardiologists were listening.
The variation between cardiologists was expected to be the most easy to resolve but the variation within dogs was thought to be a much more' difficult issue. I don't think it is yet entirely clear with such dogs whether the higher or the lower score is the more valid. This may only be resolved with post-mortem examinations of hearts but, other variable factors can affect blood flow and, hence, loudness of murmurs over short periods. For example, if there are long intervals between heart beats, as .in hyper-fit animals, more blood is pumped with each beat so that any murmurs are amplified. Conversely, in less fit animals, there may be smaller intervals between beats so that no murmurs may be heard.
Excitement itself may also affect murmurs as it appears that constriction of the blood vessels may be induced. This again increases blood flow to amplify murmurs. A further factor is that dogs' hearts do not beat regularly like ours, so that blood velocity and hence any murmurs present may automatically vary. The complications seem enormous. However, according to Miss Fuentes, normal dogs of non-aortic stenosis breeds do not develop murmurs under any of these "normal" conditions. This suggests that all Boxer murmurs are indicative of heart abnormality and that maximum grades rather than minimum grades may be the most valid.
Both the variation between cardiologists and the variation in murmurs within individual dogs were tackled at the second meeting held this past November in Coventry. Here, 15 dogs were repeatedly examined by each of 14 cardiologists and with much discussion and the use of multiple headed stethoscopes the following criteria were laid down for grading:
1. Grading should be carried out in relationship to other heart sounds to minimise hearing or stethoscope differences;
2. When a point of maximal murmur intensity is localised with a lower score heard elsewhere, the grade of the localised murmur should be given;
3. When the murmurs vary markedly with respiration and/or sinus arrhythmia, the average grade should be allocated;
4. Where a decision between two grades is not easily made, the higher grade should be given if there is a marked radiation/spreading out of the murmur and/or the murmur is of more than brief duration;
5. When a murmur increases in intensity with minor levels of excitement, the higher grade
should be given.
Such detail may be of little relevance to most of us, but it does give some idea of the complexity of the grading with minor (grade 1-2) murmurs and shows that grading involves more than an assessment of loudness.
The issue of establishing an expert panel for Boxer heart testing was further discussed at Coventry. Although the details have not yet been finalised, it seems likely that the panel will comprise those cardiologists who have attended the Towcester and/or Coventry heart testing sessions. This applies specifically to the standard stethoscopic testing. Therefore, it will be important for all of us to recognise henceforth that it is only the "panel cardiologists" that can be used for the Breed Council Control Scheme and Heart List purposes. The list of panel cardiologists will be published as soon as available and will be included in future Heart Lists
Another issue that was raised at both meetings and which is highly pertinent to assessment of aortic stenosis is the use of Doppler echocardiography. Edinburgh has led the world with the use of Doppler and the experience gained has suggested that it may take up to 18 months of regular use to obtain consistent Doppler readings. Without such experience, Doppler scores may be meaningless. A need was, therefore, seen for a panel of appropriately experienced vets, specifically qualified cardiologists, to conduct Doppler testing for the Boxer heart scheme. Again, a list of cardiologists having the necessary experience is to be drawn up.
Finally, there is the problem of the more rigorous heart testing that we all now face. This appears to have exclusively affected the proportions of dogs with the minor murmurs, Thus, when serious grading first started in 1991, the proportions of Grade Os, 1 sand 2s was 45%, 280;0 and 20%. Last year the equivalent figures were 19%, 43% and 30%. This, in effect means that with the longer and more careful listening, murmurs have been found in dogs that would previously have been considered murmur-free (Grade Os, and some Grade 1 s have been pushed up to Grade 2s.
This shift in the grading has two consequences. It means that parents and progeny have been scored differently and, for me, this enormously complicates genetic analyses. More importantly for all of us, it means that a higher proportion of clinically normal dogs fail the heart testing, and to take 30% of dogs out of the breeding population is too harsh for any control scheme. It was for this reason that I have wondered whether a change in the breeding recommendations might be warranted. However, given that about half of Grade 2s may gain Grade 1 s on retest or pass on Doppler, the level of selection (150;0 plus the more serious Grade 3s and worse) perhaps remains acceptable.
In summary, issues concerning aortic stenosis in Boxers in 1997 have revolved around reappraisal of the cardiologists' scoring systems. The vets involved have done much to eliminate individual variation in the scoring and to adapt the scoring procedures to cope with the additional complications recognised. An expert panel for standard stethoscopic testing and another for Doppler use are being set up and this should ensure yet more consistent scoring. It is therefore up to us again to exploit the improved scoring system.
But there is one other major drawback; we still do not have the post-mortem evidence in Boxers to show that all the variations in murmurs discussed are caused by specific heart abnormalities. This information is essential to verify the basis for our selective breeding programme. Please think about donating the hearts of previously heart tested dogs for research when they die, no matter what the cause of death. I know from personal experience that this is very difficult to do. It may be better arranged in advance. Please contact me for details if you are willing to help with this research.