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"THE
MORE WE LEARN THE LESS WE KNOW":
A
Progress Report to the ABC Membership
May 7,
2001
by
Kathryn M. Meurs, D.V.M., Ph.D.
(Published on the
Boxerunderground website http://www.boxerunderground.com)
Due
to a scheduling conflict that demanded her early return to OSU, Dr. Meurs
was able to give only a brief report to a small room of interested people
during judging of the Futurity classes.
THE MORE WE LEARN THE LESS WE KNOW
The
theme of Dr. Meurs’ talk was that although she has learned a great deal
about Boxer Cardiomyopathy from her research and the work of other
researchers, there is still no definitive proof that would enable her, or
any other research scientist, to give us a "cutoff point" (numbers of VPCs)
for removal of dogs from our breeding programs. Dr. Meurs said much more
research was needed before we arrived at that point, and urged boxer
breeders to Holter test our breeding stock yearly, choose a course of action
that seems right for our own breeding programs, be honest and forthright
with our fellow breeders, and most importantly, remain nonjudgmental about
breeders who make different choices.
WHICH TESTS ARE NECESSARY?
Dr.
Meurs began her talk by responding to a question about which heart tests she
considered necessary. She said that she considered a one-time echocardiogram
at over a year of age and a yearly Holter to be necessary for potential
breeding dogs. She then posed the question of what is a normal Holter
test. In a study of 51 non-boxers, the average number of VPCs per dog was
two. The range was from 0 to 24 VPCs. For boxers, Dr. Meurs said it is
probably not normal for a dog to have 100 VPCs in 24 hours. However, as
noted above, she said she cannot yet recommend a cutoff point for removing a
dog from a breeding program.
GRADING BCM
For
purposes of her study, Dr. Meurs and her associates have devised a grading
scheme for Holter test results. A Holter test that results in only single
(isolated) VPCs = Grade 1; the presence of couplets and triplets = Grade 2
or 3; the presence of runs of 4+ VPCs = Grade 4. Grades 1 and 2/3 have NOT
been proven to be connected to sudden death.
PATHOLOGY AND INHERITANCE
Dr.
Meurs said that in necropsies of all boxers that had died of BCM, a fibrous,
fatty tissue infiltration in the myocardium of the right ventricle was
found. This is similar to what is seen in a human heart disease, and may be
what causes the electrical conduction disorder in boxers. Dr. Meurs believes
that BCM is definitely inherited in an autosomal dominant manner.
MEDICATION
Dr.
Meurs said that medication must lower the numbers of VPCs by 85% to be
considered effective.
WHAT HAVE WE LEARNED?
1.
That cardiomyopathy is primarily an electrical disease in the boxer.
2.
Therefore, the disease should be called "Boxer Arrhythmic Cardiomyopathy."
3.
Most affected boxers have normal echocardiograms.
4.
Many affected dogs have NO symptoms.
HOW MANY NON-SYMPTOMATIC BOXERS IN THE STUDY HAD VPC’S?
Of
the 188 mature boxers in Dr. Meurs’ study, 157 had no clinical signs of BCM,
while 31 had fainting spells (syncope). Of the 157 dogs WITHOUT clinical
signs (symptoms) of BCM:
More
than 80% had at least one VPC/24 hours.
50%
had greater than 10.
More
than 30% had greater than 50.
More
than 30% had greater than 100.
More
than 20% had greater than 500.
Only
a tiny percentage of dogs without symptoms had greater than 3000.
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