Heart News - Progress, Problems, Complications and Conclusions

by Bruce Cattanach
Boxer '94
(pages 80-82)

It seems remarkable that heart testing in UK Boxers is now beginning its fifth year. The testing for aortic stenosis started with the stethoscopic survey on heart murmurs by cardiologists at the British Boxer Club's championship show in 1990, followed by the Scottish. Since then heart testing at shows, and to a lesser extent at private clinics, has expanded year by year such that as of now about 1750 Boxers have been examined, some more than once. Importantly, most are from the top show section of the breed, and therefore are owned by top breeders of the day. This bodes extremely well for progress in ridding the breed of this particular heart problem.

The success in breeding Boxers with sounder hearts of course also depends upon the aortic stenosis being inherited, and upon its mode of inheritance being straight forward enough to merit the degree of time, cost and effort involved. Despite some problems with the testing, which I will go into shortly, it is now clear that the disease is inherited, the mode of inheritance is fairly simple, the control system is workable, and therefore that breeders should be able to effectively breed away from the problem. The evidence for this is provided by the latest summary of the breeding results (see Table). This continues to show a clear trend for the "best" parents to produce highest proportions of the "best" progeny, and for the "poorest" parents to produce the lowest proportions of sound offspring. Generally, therefore, all continues to go well.

However, there are still problems to be resolved and these relate to those dogs with more serious murmurs deriving from the "best" parents. At present, the appearance of such dogs can be interpreted in a number of different ways, all of which may be valid:

1) The inheritance might not be quite as simple as an ordinary dominant inheritance. But this we can leave aside for the moment; the selective breeding recommended to reduce the incidence of dogs with more serious murmurs fully covers this contingency.

2) As pointed out in a previous report, the severity of the grading has increased from the time the original surveys were done. Today's progeny are therefore being graded more rigorously than some of the parents.

3) The standard stethoscopic testing does not distinguish between the murmurs caused by aortic and pulmonic stenosis. Thus, as in previous years, dogs are again being found which have Grade 4/5 murmurs, but on Doppler scanning have proved to have pulmonic stenosis, not aortic stenosis. Some of the more minor murmurs detected will also surely be due to this disorder. However, although pulmonic stenosis may complicate the inheritance picture for aortic stenosis, the detection of such affected dogs is not really detrimental to the control scheme. Rather, the selection against dogs with either type of murmur can only be good for the breed.

4) Despite earlier findings to the contrary, a level of variability in the grading by the cardiologists now seems a possibility. This is a bit of tricky situation as these vets are all experts, but their response to the evidence is both positive and concerned. The result is that groups of two or more cardiologists may conduct the testing at some of this year's shows. They will then be able to compare their findings directly. I should stress that in the short run such action will not mean more rigorous scoring. The "best" results will still be provided. But, in the long run, better standardisation of the grading should be attained.

5) A single isolated result may also be of significance. Here I refer to post-mortem findings upon my own dog, Ch Garnet Gelert of Steynmere who had to be put down recently because of a non-heart-related illness. Miss Fuentes has been seeking hearts from murmur-free or Grade 1 Boxers that have died at any age and from any causes. Gelert had a Grade 1 murmur, as ascertained by two independent vets, and his Doppler velocity was within the set "normal" range (under 2.00m/s). Knowing that there has been little response to Miss Fuentes' appeal, I felt compelled to have the old boy's heart sent up to Edinburgh. And the effort was informative. "Subtle" lesions consistent with aortic stenosis were found in the left ventricular outflow tract ("area of pale tissue below one of the aortic valve leaflets suggestive of intramural fibrosis, and another triangular shaped fibrosis plaque below one of the other leaflets, about 5mm x 3mm").

The minimum conclusion from this single dog study is that not all dogs with grade 1 murmurs are necessarily free of aortic stenosis; but equivalent findings on other dogs will need to be obtained before a definite conclusion can be reached. The fact remains, however, that as of this moment Gelert is the only "normal" dog that has yet been studied. I know it is not easy to send heart material away for examination when an old friend dies but, from personal experience, I can only say that if one sees the light of life fade from the eyes, so that only the body shell remains, it is somewhat easier. Anyone who is prepared to help with further such investigation should have their vet send the heart, in formalin, to Miss Fuentes in Edinburgh.

While the control scheme for aortic stenosis is working well and should work even better with improvements in testing, two other complications concerning Boxer heart matters are coming to light. These may not have an hereditary basis, but are still worrying in that they are not understood. One concerns a cluster of cases of myocarditis in young pups aged about 12 weeks, most associated in some way with one kennel. This particular heart condition has been attributed to viral infections and thus is liable to affect dogs of all breeds. But the chief culprit of past times, parvovirus, is no longer really with us, and all the cases known are Boxers. Glasgow Veterinary School is equipped to deal with investigations of this type but, down south, cardiologist Malcolm Cobb of Flitwick Referrals, Beds, is setting up to identify the virus. So any further cases should be referred to these centres. The symptoms are weakness, lethargy, breathing difficulties, swollen belly, heart murmurs and/or abnormal heart rhythms. Any such sick puppy should be rushed through for referral while alive. Post-mortem material is of no use. If the pup has to be put down, the heart is removed immediately and has to be snap frozen in liquid nitrogen for subsequent study.

The second situation is almost more worrying. Here three adult dogs have died within 2-3 weeks, one 7 weeks' pregnant, and all within one kennel. The diagnosis has been cardiomyopathy. Now this heart condition is relatively prevalent in American Boxers and has an hereditary basis. But, with these British cases onset followed what appeared to be kennel cough, seemingly not just the cough associated with this particular disease. So, again, there a suspicion that a viral factor just might be involved. Apparently there is some precedence for this in human cardiomyopathy. But the known Boxer cardiomyopathy is apparently quite specific. Apparently it differs from the cardiomyopathy of most other breeds and is associated with reduced plasma levels of L-carnatine, a substance that is essential for the transport of fatty acids as the energy source of cells. Treatment is possible. I should state that Miss Fuentes has spent a huge amount of time and effort on these two heart conditions, with phone calls around the country and also to America. A lot is being done for Boxers!

I should finish on a positive note, and this is not too hard to do.

- The above complications of seemingly new heart problems are worrying, inherited or not, but actions to deal with both are in hand.

- The testing system for heart murmurs has some problems and, again matters are in hand to deal with these. However, with or without the indicated difficulties, the stethoscopic testing is working well enough to allow breeders to select for sounder stock.

- As to the prospects for the breed as a whole in dealing with aortic stenosis, here the only difficulty lies with the large numbers of dogs with the murmurs. Once only Grade 0 or Grade 1 stud dogs are available there will be a rapid improvement. But the greatest surge forward will come when Grade 2 bitches are no longer a breeding necessity for anyone. Progress for the breed as a whole should then be rapid, as it is for individual kennels even now.

Analysis of Breeding Records (To Dec. 1994)