IntroductionWell bred boxers have the potential to live long and happy lives. However, if breeders don't take enough care, it is possible for boxers to be afflicted by either of two hereditary heart problems – (1) Cardiomyopathy (BCM/ARVC), and (2) Aortic Stenosis (AS). Both conditions can be tested for.
This document summarises the latest information on testing from research carried out on the conditions, and recommendations made by Boxer Clubs overseas. It is updated from time to time and feedback is welcome. NB: Please don't copy this information without permission [Last update Feb 2014]
Boxer Cardiomyopathy (BCM or FVA or ARVC)Cardiomyopathy is one of the most common causes of sudden/unexpected death in boxers, both young and old. Dogs with cardiomyopathy often show no symptoms until they have a cardiac arrest.
Boxer Cardiomyopathy (BCM) is different from the cardiomyopathy in other breeds and is more correctly called 'Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)' as it's an electrical problem rather than a disease of the heart muscle itself - that's why it's so hard to detect. It's like a heater with a damaged wire inside - it may only short out sometimes without any outward sign, and the heater may seem good as new until you get a complete meltdown.
The disease involves an electrical conduction disturbance which causes the heart to contract too early, producing an extra, ineffective beat - called Premature Ventricular Contraction (PVC or VPC).
When there is a run of many of these PVCs together, the heart muscle can’t produce a normal, effective contraction, which results in a lack of blood flow to vital organs including the brain and the heart itself. This can cause the dog to experience a seizure-like or fainting episode (syncope). These episodes can be missed or confused with epilepsy or other causes of collapse. A long sequence of PVC's can lead to complete cardiac arrest and death.
Recent research has found a gene that is linked with ARVC in Boxers and so a DNA test is now available. Dr Meurs who developed the test states on the test result form that a Negative (clear) result does NOT mean the dog won't develop the disease, and that a positive (affected) result does NOT mean the dog will develop the disease. This suggests that the test is not a reliable indication of the health of a dog's heart. The test has been controversial with many anedotal reports of dogs whose DNA results do not make sense (eg dogs with ARVC diagnosed and medicated but who receive negative results on the DNA test). There have also been comments that in humans there are several genes responsible for a very similar heart problem so questions over whether the single gene identified in Boxers is the full picture. The jury is still out. What is agreed by all the experts (including those who developed the DNA test) is is that other forms of testing (holtering) should still be carried out (see below).
The main tool for screening for PVC's is a 24 Hour Holter Monitor examination, which records the dog's heart activity over an extended time. The monitor is strapped to the dog and electrodes are placed on the chest while the dog goes about its normal activities. The total number of beats, including the abnormal PVC's are recorded. Single PVC's are less dangerous than runs of PVC's.
PVCs appear to be relatively common in dogs - a recent study tested 50 healthy mature dogs of various breeds and found that 16 of them had between 1-24 PVCs. So a low number of PVCs is nothing to panic about. However, larger numbers of PVCs or pairs or runs of PVCs are a concern: You can imagine that if there are many of these ineffective beats, or several in a row, the heart output is affected and that has to have consequences for the health of the dog in the long run - either through the heart having to work extra hard to compensate or through the body/brain getting insufficient blood supply
Currently a result with less than 50 PVCs in a 24hr period is considered ‘normal’. Between 50-100 PVCs (not in runs) is also acceptable if the results are consistent on re-testing. Re-testing of a dog with 0-100 PVCs is required because the disease progresses over time and because oter temporary conditions may cause PVCs. Repeating the Holter test every year is advised.
If a dog has more than 100 during the 24hrs on repeated tests, they can be considered to have the disease and therefore be likely to pass it on to their progeny. However, the recommendation is to look at the 'big picture' in terms of the longevity of the lines, results of heart tests for relatives, and whether any relatives have displayed symptoms of heart problems.
Aortic (AS or SAS) Aortic Stenosis is a developmental defect where there is a narrowing under the aortic valve in the heart, meaning blood flow is disturbed and the heart has to work harder to get the required output. The reduced blood flow can produce symptoms of fainting (syncope) and in severe cases even sudden death.
The defect means that there is turbulence in the blood flow, resulting in a murmur (or quiet whooshing noise) that can be heard with a stethoscope (but note that there can be many causes for a murmur so further investigation via cardiologist is recommended). The degree of severity of the defect will affect the strength of the murmur. If the disease is severe and there is a significant narrowing of the valve, then blood is squeezed through resulting in turbulence and higher blood flow speed. The speed of the blood flow can be measured to provide an indication of the severity of the disease. There are guidelines regarding the maximum flow (now 2.4), providing there is no evidence of structural causes.
Aortic Stenosis develops as the dog’s heart grows, so assessing a young dog can be misleading. Many puppies have innocent murmurs, often referred to as ‘puppy murmurs’ or ‘flow murmurs’ - most disappear by about 16 weeks of age. Even if the puppy murmur persists there may be no cause for alarm so long as they are quiet - genuine "flow" murmurs are not associated with heart disease in the adult. On the other hand, a pup that is free of murmurs at 8 weeks of age, may develop a serious murmur by the time it is mature. A recent recommendation is to have dogs checked over 24 months old as murmurs have been found to develop only after sexual maturity. However, many cardiologists still test from 12 months.
The best way to diagnose AS is to have an adult dog’s heart listened to by a cardiologist. The murmurs are graded – usually on a scale from 0-5, with 0 being a clear heart free of any murmur. Ideally a murmur will be investigated further using devices like Doppler to check on the cause and nature of the murmur and resulting changes in blood flow.
The current recommendation is that a murmur of less than Grade 2 is unlikely to affect a dog’s quality of life and is acceptable for breeding. Re-testing of a Grade 0 or Grade 1 murmur is not normally required.
Murmurs of Grade 2 or greater warrant further investigation through Doppler echocardiography.
Frequently asked questions about heart testingHow do I get access to heart tests?
The links above give you access to information on testing. Your vet may also be able to help with information (though many are not aware of the diseases specific to boxers). Vet schools or specialists often have facilities for testing. Some cardiologists travel around offering clinics. Information on testing for BCM is available on this page
Why test if there have been no heart problems in my dogs?
Research indicates that Boxer cardiomyopathy is ‘autosomal dominant’, that means that, statistically, if you breed from a dog with the condition half the litter is likely to be affected. What makes it difficult is that dogs with BCM may show no sign of the disease until later life.
Each time you choose a stud dog you risk bringing serious hereditary problems to your line and it may take several years before you see the consequences.
So, your line may be very healthy at present, but perhaps the stud dog you’ve just used carries the gene for BCM. All may seem fine until 4 years from now when one of the dogs from the litter collapses, or even dies suddenly…In the meantime perhaps you’ve bred on from a pup you kept from that litter. You may have many walking time-bombs out there.
It is much easier to avoid getting into that situation than to have to rethink your whole breeding programme and deal with distressed puppy owners and a ruined reputation. Testing needs to become common to provide all breeders with choices when they are looking at stud dogs or new bitches to bring into their lines.
Why didn’t my vet mention they these tests?
Your local vet is not as familiar with Boxer heart conditions as the cardiologists and geneticists who have done the research and determined the best screening methods.
What makes it complicated is that Boxer cardiomyopathy is different from cardiomyopathy in other breeds. Unless your vet is a specialist cardiologist who has read the latest research on boxer cardiomyopathy, don’t assume they have all the information on the condition.
When you think about it, a human with a specific hereditary heart condition is likely to be referred to a cardiologist who is an expert in human heart conditions. Why would we expect that a local vet (the equivalent of a GP) would be an expert in treating a heart condition in our dog, especially a condition which is only now getting thorough research done on it?
My vet listened to my dogs’ hearts and said they are fine. Isn't that enough?
Boxer cardiomyopathy can NOT be detected by simply listening to a heart so this kind of ‘testing’ will not safeguard your breeding programme or your puppy buyers.
The murmurs consistent with Aortic Stenosis can be detected by listening to the heart, however, overseas breeders rely only on a ‘board certified’ cardiologist when it comes to interpreting and grading murmurs so use caution when relying on a vet’s grading of a murmur – further investigation may be warranted.
My dogs have been Doppler checked - isn't that enough?
As mentioned in other answers, Boxer cardiomyopathy is different from cardiomyopathy in other breeds and Doppler tests are NOT a useful tool for detecting it. A Holter Monitor is the only reliable way of detecting the VPCs that signal BCM. Doppler testing IS used in the assessment of Aortic Stenosis and can be a useful test there. Even then, the regimes recommended in the UK and by the American Boxer Club suggest Doppler only as a follow-up test if a murmur is detected. So if an experienced vet listens to your dog’s heart at 2 years old and hears no hint of a murmur then you’re probably wasting your money if you go to a Doppler test.
I had an ECG done on my dog why would I need to do a Holter test?
Unfortunately an ECG just isn’t long enough to detect the runs of irregular beats that a Holter can detect. That’s because an ECG will cover only a few hundred heat beats. A 24 hour monitor will measure tens of thousands of beats. The irregular beats that are a sign of BCM often come in clusters or runs so a long and continuous period of testing is the best chance of ‘catching’ them. The researchers have confirmed that many dogs with Boxer Cardiomyopathy get false clear results on an ECG.
Only American lines have cardiomyopathy / only UK lines have aortic stenosis so aren't my dogs safe?
If only it were that simple! Unfortunately this is simply not true. My own experience of cardiomyopathy in New Zealand was from purely British lines back many generations.
The problems may have a higher incidence or higher awareness in particular countries but all boxers started from a common gene pool and the genes for these life threatening problems are all countries.
My dog is super-fit and the parents lived to a good age so why would it need a heart check?
Fitness levels have nothing to do with whether a dog carries a gene for a heart condition that can lead to sudden death – it is not like the stereotypical image of someone with heart problems that we see on telemovies, dogs can be strong and active until they collapse - my dog that died from BCM certainly was a picture of good health until the end.
As for longevity, do you know how long all the littermates of those parents lived? or how long the littermates that were culled might have lived? or how long the brother that got hit my a car might have lived?
Remember that these conditions don’t necessarily affect the whole litter and also don’t necessarily show symptoms until later life.
It may be easier to visualize in the case of BCM: the heart muscle and valves are in good condition and outwardly function normally. Unfortunately the electrical impulses that tell them when to operate are unreliable. The electrical triggers may work fine for many years, causing only minor and irregular fluctuations to the rhythm of the heart. The irregularities can become more frequent and eventually can affect the ability of the heart to pump enough blood through – leading to collapse or other signs of heart disease. In some dogs it may not get to that point at all – they may live to a good age but still pass on the condition to their offspring who may not be so lucky.
People have been breeding boxers for years without these tests, why do we need to start doing them now.
People thought that 'bleeding' someone helped cure diseases for many years. Times change as knowledge of how to solve problems increases.
Advances in communication technology mean that it is easier for people to get information these days and as time goes on, more and more breeders and puppy buyers will know about heart problems and will be asking whether your dogs have been tested.
My dog doesn’t have a heart murmur so doesn't that mean it is fine for breeding?
If you dog’s heart has been listened to by a vet with good knowledge of detecting heart murmurs, then the lack of a murmur is a good indication that your dog is free of serious Aortic stenosis. However, BCM does NOT have anything to do with murmurs. All the boxers I knew well personally who died from BCM (all before they reached the age of 6 years) were murmur free, super-fit dogs who had been ‘checked’ by vets all their lives and in some cases had also had ECGs done.
None of these tests are certain so don't we lose good dogs from the gene pool for no reason?
Biopsies to detect whether lumps are malignant are not certain. Pap smears to detect cervical cancer are not certain. Breast examinations to detect breast cancer are not certain. Screening is about increasing knowledge and reducing risk.
One stud dog carrying heart problems, over generations could lead to literally hundreds of dogs with shortened life expectancy. If the test sometimes get it wrong (and we don’t really know for sure that they do), it still seems to high a price to pay to ignore the tests.
As far as reducing the gene pool - There is no one boxer that has some magic attribute that is vital to the future of the breed. The gene pool is not so small that we cannot risk excluding a few dogs for the sake of the health of the breed.
The dog who ends up a fashionable stud dog probably had some plain brothers who could equally have provided the same ‘genes’ to the boxer gene pool and we don’t moan and complain that those plain coloured dogs in pet homes are lost from the gene pool. Surely any risk of a dog passing on a fatal condition should be considered significant enough to outweigh everything else.
I know of dogs who have had murmurs and lived to a good age – do these tests have anything to do with longevity?
As noted elsewhere, BCM has nothing to do with murmurs and it’s a killer.
As for aortic stenosis, well, yes a dog with a deficiency in their heart can often still live to a ripe old age, but that doesn’t mean we want to produce future generations of dogs with that same deficiency does it?
But note that there are degrees of murmurs and some murmurs are harmless. The testing regimes have good guidelines on what’s OK and what isn’t and on appropriate tests to work it all out.
My vet said my dog’s murmur was harmless so why do I need to do expensive tests?
As noted elsewhere, BCM has nothing to do with murmurs and it’s a killer.
Is your vet a cardiologist? There are degrees of murmurs and some murmurs are harmless. The testing regimes have good guidelines on what’s OK and what isn’t and on appropriate tests to work it all out. If those guidelines haven’t been followed then you can’t be sure that you won’t be producing future generations with heart problems.
It’s also important to look beyond just one dog. Perhaps one dog from your litter has a murmur that may have been due to something other than AS. The only way to be certain is to be regularly testing all your dogs so that you get a clear picture of the incidence of AS and BCM within your lines – then any anomalies can be recognized for what they are.
If these tests are so important why aren’t they recommended by the Clubs?
Many clubs around the world DO recommend them. See the American Boxer Club site, and the American Kennel Club is funding some of the research into BCM.
Clubs are made up of people just like you who don’t necessarily have a lot of knowledge about heart problems. Until it affects you personally, AND you choose to take responsibility and face up to it, you’re unlikely to go out and find the information and even if you do, you may be embarrassed to raise it with your club.
The process needs to start with people learning about the problems, then we can start to agree on what to do about them.
Further readingGeneral sources:
American Boxer Club – Health resources:- http://www.americanboxerclub.org/health/healthfr.htm
Kathryn M. Meurs, Alan W. Spier, Matthew W. Miller, Linda Lehmkuhl and Jeffrey A. Towbin, Familial Ventricular Arrhythmia in Boxers :- http://www.boxerclubofarizona.org/meursfva.htm [no date]
Michael R. O'Grady, DVM, MSc, Diplomate ACVIM (Cardiology) M. Lynne O'Sullivan, DVM, DVSc, Diplomate ACVIM (Cardiology) How does Boxer Cardiomyopathy differ from canine dilated cardiomyopathy? :- http://www.vetgo.com/cardio/concepts/concsect.php?conceptkey=105#105
Selected articles from the Boxer Underground online magazine:- http://www.boxerunderground.com
- 2005 Report from Dr Meurs
- 2004 ABC Health Testing and Reporting Guidelines
- Dr. Meurs Reports To The Abc 2001
- Boxer Cardiomyopathy By Wendy Wallner, Dvm
- Recommendations For The ControlOf Aortic Stenosis (October 1993) ByBruce Cattanach, Steynmere Boxers, UK
- Handout Sheet On Boxer HeartMurmurs For New Puppy Owners
- EverythingYou Always Wanted To Know About Aortic Stenosis
Peer-reviewed research on BCM (in descending date order):
Spier, AW, Meurs, KM Assessment of heart rate variability in Boxers with arrhythmogenic right ventricular cardiomyopathy JAVMA-J AM VET MED A 224 (4): 534-537 FEB 15 2004
Spier, AW, Meurs, KM Evaluation of spontaneous variability in the frequency of ventricular arrhythmias in Boxers with arrhythmogenic right ventricular cardiomyopathy JAVMA-J AM VET MED A 224 (4): 538-541 FEB 15 2004
Koplitz, SL, Meurs, KM, Spier, AW, et al. Aortic ejection velocity in healthy Boxers with soft cardiac murmurs and Boxers without cardiac murmurs: 201 cases (1997-2001) J AM VET MED ASSOC 222 (6): 770-774 MAR 15 2003
Meurs, KM, Spier, AW, Wright, NA, et al. Comparison of the effects of four antiarrhythmic treatments for familial ventricular arrhythmias in boxers J AM VET MED ASSOC 221 (4): 522-527 AUG 15 2002
Kraus, Marc S., Moise, N. Sydney, Rishniw, Mark, et al. Morphology of ventricular arrhythmias in the boxer as measured by 12-lead electrocardiography with pace-mapping comparison Journal of Veterinary Internal Medicine 16 (2): 153-158 2002
Meurs, KM, Spier, AW, Miller, MW, et al. Familial ventricular arrhythmias in boxers J VET INTERN MED 13 (5): 437-439 SEP-OCT 1999
Meurs, KM, Spier, AW, Wright, NA, et al. Comparison of in-hospital versus 24-hour ambulatory electrocardiography for detection of ventricular premature complexes in mature Boxers J AM VET MED ASSOC 218 (2): 222-224 JAN 15 2001
Use of ambulatory electrocardiography for detection of ventricular premature complexes in healthy dogs / Meurs, Wright, Speir & Hamlin 2001 :- http://avmajournals.avma.org/doi/abs/10.2460/javma.2001.218.1291
Spier, A. W., Meurs, K. M., Linn, C. G. Signal-averaged ECG in the assessment of arrythmogenic cardiomyopathy in boxers Journal of Veterinary Internal Medicine 15 (3): 307 2001
Spier, AW, Meurs, KM, Muir, WW, et al. Correlation of QT dispersion with indices used to evaluate the severity of familial ventricular arrhythmias in Boxers AM J VET RES 62 (9): 1481-1485 SEP 2001
Goodwin JK, Cattiny G A href="http://www.vetheart.com/boxerab.htm">Further characterization of boxer cardiomyopathy Proc 13th ACVIM Forum 1995; 300:- http://www.vetheart.com/boxerab.htm
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