WE SHALL KEEP YOU INFORMED VIA THE BULLETIN AS WE PROGRESS WITH THESE
NEW INITIATIVES.
Following is a Synopsis of the CKCSC, USA Heart Symposium. A complete
transcript, to include photographs, slides, graphs, etc., will be made available for those
who were unable to attend or anyone who is interested. In future Bulletins watch for
ordering information.
DR. ANDREW BEARDOW, now in private practice at the Veterinary
Referral Centre in New Jersey, moderated and gave an overview of the symposium, saying
that it was designed to give different perspectives in order to develop a pragmatic
approach to MVD.
The mitral valve, located on the left side of the heart, is crucial to
how blood is circulated through the body. MVD destroys this structure. Many breeds develop
MVD but in Cavaliers it occurs with a high frequency, starts much younger in life,
progresses more rapidly and usually kills them.
There are various ways to examine the heart – auscultation
(listening with a stethoscope for murmurs), radiography (chest x-rays to see the size of
the heart and the presence of fluid in the lungs) and echocardiography (ultrasound to
visualize the heart). Doppler ultrasound will also show flow through the heart, the most
sophisticated form of which is 2 dimensional, color-flow Doppler in which blood flow is
color coded based on its direction.
Research has shown that MVD in Cavaliers is a significant problem
EVERYWHERE in the world. This add credence to the fact that MVD is a genetic disorder.
DR. JAMES BUCHANAN, Professor Emeritus of Cardiology at the
University of Pennsylvania, presented many interesting pathologic slides showing the
devastation caused by MVD. He noted that 2 other conditions are more common in Cavaliers
than other breeds. Patent ductus arteriosis (PDA) is a congenital (i.e. – present at
birth) heart defect which can be corrected with surgery and which is found at 6 times the
rate in other breeds. Cavaliers with PDA, whether corrected or not, should NOT be bred.
Femoral artery occlusion (FAO) is unique to Cavaliers, having not been seen in any other
breed. It causes no problem since other arteries take over for the blocked femoral artery.
Diagnosis is made when the pulse on the inside of the dog’s rear leg(s) is found to
be weak or absent. An inherited weakness in the artery wall is suspected.
Heart murmurs are graded from 1 to 6 (the worst). Grade 1 murmurs are
barely audible in a quiet room while grade 6 murmurs can be heard before the stethoscope
actually touches the chest wall and, in some cases, without a stethoscope at all.
He stated that there has been no statistical improvement in Cavalier
hearts since his initial report which covered 1987-1991. He’s found no sex difference
in onset of murmurs. Systolic clicks occur 25 times more frequently in Cavaliers than
other breeds and may be a precursor to a murmur showing up a few years later. He’s
not prepared to say you shouldn’t breed a dog with a click but it raises the level of
suspicion.
Vertebral Heart Size (VHS) is a quantitative way of measuring heart
size, based on a chest x-ray, and thereby objectively determining heart enlargement.
DR. VIRGINIA LUIS FUENTES, Visiting Lecturer in Cardiology at the
University of Missouri (formerly of England), worked with Dr. Peter Darke, noted British
cardiologist, in Scotland for 7 years and was on the heart sub-committee for the English
CKCSC.
In 1987 at a UK dog show Dr. Darke examined 431 Cavalier and found that
50% of 5 year old Cavaliers had mitral valve murmurs, that there was a high prevalence of
murmurs between 2 and 4 years of age and that ALL Cavaliers from 11-13 years old had
murmurs. This was an alarming finding and the English CKCSC took action.
A scheme was started using a 2 part form to be filled out by any
veterinarian, indicating whether the Cavalier had a murmur or not (no grade noted). The
owner kept one copy and voluntarily sent the other to the Club. This scheme ultimately
failed because there was no data published and breeders were given no guidelines by the
English Cavalier Club.
A few years ago, following publication of the Swedish Cavalier heart
study, a new scheme was implemented using a computer database tied in with English Kennel
Club records. They also enlisted the services of an epidemiologist, James Wood. A booklet
of Cavaliers with clear hearts at 5 years old (not all cardiology checked) was published
and will be updated. It was felt that they need to have more older dogs
cardiologist-checked and having heart clinics apart from shows, like those started in the
US in the Northeast, is a very good way to accomplish this.
Their breeding recommendations follow the Swedish guidelines of not
breeding a Cavalier before it’s 2 ½ years old and murmur free and only if its
parents are murmur free at 5 years old. Don’t breed any Cavalier that gets a murmur
before the age of 5.
In the US, you have the opportunity to set up a good breeding protocol,
learning from the British experience and avoiding their mistakes.
LENNART SWENSON, M.Sci., geneticist at the University of
Agricultural Sciences in Uppsala, Sweden, genetic consultant to the Swedish Kennel Club
and former breeder/exhibitor of Skye Terriers discussed how to develop breeding strategies
to control inherited diseases. "You must have valid information obtained by medical
examinations of the right animals, in sufficient numbers, at an appropriate age, with the
results of these evaluations made available to the breeders."
The Swedish Heart Study was designed to find out whether or not MVD was
inherited in Cavaliers. It did just that, showing that the offspring of the most affected
parents were more likely to be more severely affected and at a younger age. Conversely,
the offspring of the least affected parents stayed healthier longer and were less severely
affected with MVD. The strong suspicion is that MVD is a multifactorial, polygenic
threshold trait, similar to hip dysplasia (HD).
As an example of how such a trait can be greatly reduced, Swenson
showed that HD in Rottweilers in Sweden was reduced from 36% to 11% between 1976 and 1994.
Initially, in order to register a litter, both parents had to have their hips evaluated
but both dysplastic and non-dysplastic Rottweilers could be bred. That information was
available to anyone who called the Swedish Kennel Club and asked. Eventually, through peer
pressure, breeders stopped breeding dogs with HD. Now, only Rottweilers without HD can be
bred. The incidence of HD has been dramatically reduced by using these guidelines.
THE BIGGEST REASON THAT BREEDING SCHEMES FAIL IS THAT BREEDERS
DON’T FOLLOW THEM! Compliance with schemes is enhanced by using relatively cheap,
simple, effective measuring methods and the publishing results for all to see.
The main difference between the Swedish Heart Study data and data
gathered in other countries is that in Sweden, more 5 year old males than females had
murmurs (55% vs. 35%). Elsewhere the ratio was roughly 50-50.
DR. BRUCE KEENE, Associate Professor of Cardiology at North
Carolina State University, spoke about developing a screening program, deciding what tests
to use and how best to allocate our resources. As well as developing a breeding protocol,
we might also think about funding research into drugs or techniques that can benefit
Cavaliers that have or will get MVD. This would be one of the roles of the newly
established CKCS Health Foundation.
He presented the findings of a Swedish study that compared the accuracy
of detecting MVD through auscultation (stethoscopic examination) by a cardiologist versus
echocardiography. A cardiologist’s auscultation was found to be 90% accurate and due
to its wide availability and low cost, he felt it should be the method of diagnosis for
screening Cavaliers for MVD and for determining the severity of their murmurs.
Unfortunately there is no perfect screening test but a test with 90% accuracy that can be
used by 100% of the people, is, in the long run, the best choice.
Dr. Beardow summarized. Keep in mind that systolic clicks may be a sign
we should consider. FAO may indicate a more generalized disease process. In some studies,
at any given age, more males than females are more affected with MVD. Parental disease
status seems to have a major effect on the probability of developing MVD and its
progression in their offspring. MVD is most likely a multifactorial, polygenic threshold
trait, similar to HD. Murmur free females with litterbrothers who have developed MVD
should be considered suspect. Breeding values based on parental status or perhaps even
earlier generations than that may allow younger dogs to be bred; thus the reason for the
UK booklet of 5 year old heart-clear Cavaliers. General considerations are that a
screening test should be widely and easily available or people will not use it. The test
should be specific enough to identify MVD but not so sensitive that we eliminate all of
the breeding stock. Testing should not be financially prohibitive. A breeding program
should be widely supported and uniformly implemented and therefore should be well
presented and well understood.
Questions and answers followed. This is a summary of the salient
points.
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In the future the UK heart registry booklet should not
just list heart-clear 5 year old dogs but also have statistical information, which would
be easily extractable from the computer database they’ve set up.
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When an asymptomatic dog first develops a mitral valve
murmur, the logical next step is to take a baseline chest x-ray, since the degree of any
heart enlargement is the most accurate way of determining how compromised the heart
function is. It’s best to have a cardiologist or radiologist read these x-rays since,
due to the Cavalier’s chest conformation, many general practitioners may incorrectly
diagnose an enlarged heart (cardiomegaly). Radiographs can be taken by a general
veterinarian and sent to a specialist.
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The availability, or lack thereof, of cardiologists
was mentioned. A list of cardiologists will be published in the CKCSC, USA, Health
Registry. The information is also available on the American College of Veterinary Internal
Medicine’s web site at http://128.120.10.3/acvim/cardiodips2.htm.
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There is no problem differentiating a PDA murmur from
a mitral valve murmur using a stethoscope.
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Might there be 2 types of MVD – that which
progresses rapidly and another form which progresses slowly? With the Cavalier heart
database in the UK, they hope to eventually answer that question but so far the
information is only anecdotal. In general terms, the earlier the onset of a murmur, the
shorter life the dog will have.
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There is a lot of individual variation in the
expression of MVD but, generally speaking, a lag time of 3-4 years was found between the
time when a mitral valve murmur is first found by a cardiologist and when clinical signs
begin to appear.
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There are a couple of ongoing prospective clinical
trials trying to determine if angiotensin converting enzyme inhibitors (ACE inhibitors
such as enalapril, the active ingredient in Enacardâ and Vasotecâ ) will
keep dogs with MVD healthier longer and delay the onset of heart failure. Results should
start to come in a couple of years. In humans these drugs have been shown to help once
heart failure begins and to prolong the interval before heart failure occurs.
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The new UK heart form for Cavaliers has a place to
grade any murmurs found and a box to check if the examination was done by a cardiologist.
Only cardiologist’s exams are entered into their database.
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Interest was shown in how and why the Swedish Kennel
Club requires heart testing in Cavaliers as a prerequisite for registering litters.
Lennart Swenson said that the Swedish Kennel Club works closely with the University in
Uppsala with regard to genetic health programs. Once a disease is shown to be genetically
based, the Swedish Kennel Club requires testing for that problem in that breed. In the
first years both affected and unaffected dogs can be bred, with the results made public.
Eventually only unaffected sires and dams can be bred. If a breeder violates these rules
they will get a letter from the Kennel Club stating that they’ve violated the rules.
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Someone asked about environmental influences being the
cause of MVD in Cavaliers. The panelists agreed that it was not logical to think that
environmental factors were the cause or that you can alter the progress of the disease by
changing the environment. There is no reason to think that the environment of Cavaliers is
any different than any other dog but it’s only Cavaliers that have this problem in
such a serious form.
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Could the use of vitamin E forestall MVD in adult
Cavaliers or prevent the development of MVD in the offspring of females given vitamin D
during their pregnancy? There was no good evidence either for or against the efficacy of
vitamin E in influencing the incidence or progression of MVD in the dogs themselves or in
their offspring. Proper clinical trials are needed.
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A question was asked about using supplements, special
diets and holistic approaches to controlling MVD and the resistance of most veterinarians
to try these things. Dr. Keene said that when several supplements, etc. were used there
was no way of knowing which, if any, might be working. There have been no clinical trials
proving that any of these supplements or approaches work. However, the CKCS Health
Foundation, once up and running, could choose to allocate funds for research into one or
more of these supplements, etc. Veterinarians feel that they must do the best possible for
their patients and thus prescribe drugs and treatments that have been proven to work. Most
do not mind if clients want to give supplements, feed special diets, etc. as long as they
don’t think any of the things would be detrimental to the dog and the client
discusses it with. If and when clinical trials support the efficacy of any of the holistic
approaches, they would have no problem using them.
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Surgical valve replacement was asked about. A few
veterinarians are using a surgerical procedure where they do cross stitching of the
annulus of the mitral valve but not valve replacement. Next week a Texas veterinarian will
report on 9 such surgeries. The cost is estimated to start at $2500. Success has not been
high, mainly because most cases are in end-stage heart failure. Earlier intervention could
yield better results. Also, putting such a small animal on heart by-pass requires special
machines. Human replacement valves are too big for a Cavalier.
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There was mention of our breed initially starting with
only 4 dogs and consequently our gene pool is very small and would Cavaliers ever be
"free" of MVD. Lennart Swenson felt that more than 4 dogs were used in the
beginning but it really didn’t matter since all breeds began with just a few dogs
(6-8 in Cocker Spaniels, etc.). He said the goal is not to rid the breed of MVD but to
have all Cavaliers die a natural death before they get MVD, then it’s no longer a
problem.
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If every, or at least most, breeders followed the
breeding protocol, how many generations would it take to see results? Lennart Swenson said
that by using the Swedish protocol and with good compliance, you would see a major
improvement in just 1 generation. However it wouldn’t be until those puppies were 7-9
years old that you would actually be able to confirm that an increased percentage of them
were still murmur free. He said in 2-3 generations you will have a much better situation
but ONLY IF YOU ACTUALLY USE THESE TECHNIQUES. He most fears that breeders will not follow
the program.
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What about developing a genetic test for MVD? MVD is
not controlled by a single gene so a genetic test is probably not possible at this time.
However there might be a dominant gene that controls the disease in 30% of the cases. If
this is true, this gene will be the first to disappear once breeders start selectively
breeding to reduce MVD and you will therefore take away the possibility of identifying
that gene BUT that is a GOOD THING.
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How has the English CKCSC been able to require their
breeders to do the heart testing and to send in the test results? Dr. Luis Fuentes was not
sure what proportion of English breeders were following the scheme but with any new
program, there tends to be a core of active, committed people versus others who don’t
want to confront the problem. Eventually people who don’t take part in the program
will become marginalized. Things such as public lists of heart-clear 5 year old Cavaliers
help bring people into the breeding scheme. Sweden is "lucky" in being able to
take control of the situation through Kennel Club mandated programs.
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How did the Swedes come up with the ages in their
breeding protocol? They used 5 years and heart-clear because of the bell curve showing
that about ½ of Cavaliers had already gotten a murmur by 5 years and 2 ½ years was
selected because it is half of 5.
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The panelists said that 14 months old was the youngest
age at which they’ve detected a mitral valve murmur.
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Some folks worried that there will not be very
many heart-clear 5 year old sires to breed to and too many dogs would be eliminated from
the breeding population. Lennart Swenson said that when breeders say they can’t
afford to cut out this much of the population they forget that they already do just that.
They only breed about 10% of males and the rest are cut out of the population because of
their lack of "beauty". Breeders are willing to make hard decisions and cut away
a lot of dogs for the beautification of the breed but when they discuss hearts, suddenly
it is different. Swenson finds that very "peculiar". (emphasis mine,
mle)
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There were many questions about specific situations
regarding when dogs get murmurs after the age of 5 (having been clear at 5 years), if they
should be bred and, if so, should it be based on the grade of murmur first noted, etc. The
discussion ended with the message that we shouldn’t get hung up on numbers and
individual situations. A protocol must be established and adhered to, even though it may
change or be updated sometime in the future. You have to have a starting point. The
panelists basically agreed on every point.
