by Martha Bowman

1. Isn’t it terribly inconvenient?

2. What exactly does the test entail?

3. Won’t the shaving ruin my dog’s chances in the show ring?

4. The test may not tell me definitively whether my dog has cardiomyopathy. Why use a test that can't even give me the information I need?

5. I already ECG and Echo my dogs every year; isn’t that enough?

6. I keep hearing that it costs hundreds of dollars per test; how can I afford that?

7. Is it really necessary? My own veterinarian said it isn’t.

8. My dogs come from a long-lived line; do I really need to test them?

9. My vet has never done a Holter, and there is no cardiologist in my area, so who is going to test my dogs?

10. . What if I Holter my dog and I get bad news?

1. Isn’t it terribly inconvenient?

Right now it is true that you can’t just run down to your regular vet and get a Holter monitor test done right when you want it. However, with a little planning, Holtering your dogs doesn’t have to be an ordeal. Once you get the monitor and familiarize yourself with its use, you can test one dog each day until all your dogs are done; you can do the monitor hook-ups in your own home, at a time that is most convenient for you, so you don’t have to deal with the inconvenience of working around your vet’s schedule, or traveling to a cardiologist’s clinic. Once all your dogs have been tested, you won’t have to test again for at least another year.

Possibly the greatest inconvenience at this time is that there are far more breeders wanting to Holter their dogs than there are monitors available for use. This has resulted in long waiting periods for access to a monitor. Fortunately, this is a surmountable problem! Many clubs have expressed interest in purchasing a Holter monitor. If individuals using the monitor are charged just a nominal cost, the club can easily pay for the materials each user needs and the maintenance of the monitor, while still saving enough to ensure that the club will be able to purchase a new monitor when it is needed. If Boxer fanciers want to ensure that Holtering is available for routine screening, however, it is we who must take the initiative to see that more monitors are purchased and made available for use by breeders and owners!

2. What exactly does the test entail?

There are currently a few clubs, veterinarians, and other individuals who will rent the Holter monitor to an owner, generally for a nominal fee. The monitor will arrive at your home with a complete set of instructions. All the owner needs to do is shave a few patches on the dog’s torso, stick on some disposable self-adhesive electrodes (included with the monitor), and snap a few color-coded lead wires on to the electrodes in the order the instructions specify. A regular cassette tape (usually included with the monitor rental fee) goes into the monitor, which is similar to a Sony Walkman. Once the battery (usually also enclosed) is inserted, the test begins. Then all that remains is to wrap some Elastikon or VetRap around the dog to hold the leads and the monitor in place, and keep the dog confined (away from other dogs) and/or supervised for the 24-hour duration of the test. Removing the monitor is as simple as removing its battery and cassette tape, and taking the tape and electrodes off the dog. There are several cardiologists who will provide tape reading for a small fee; the hardest part is waiting to hear the results of the test!

Most owners actually find that the shaved patches grow back fairly quickly. Within a month or so, they may be almost invisible (of course this depends on your own dog’s rate of hair growth). Even the most actively-campaigned dogs have breaks in their schedules, so if you can arrange to Holter your dog at the beginning of a rest period he may have a full coat by the time you are ready to show him again. Some Boxers have enjoyed success in the show ring even while sporting shaved patches from the Holter test. Judges will often simply ask the handler the reason for the shaved areas, and seem pleased to find that they are evidence of good breed stewardship by the concerned owner.

It’s very true that even a Holter with 0 abnormal beats IS NOT known to mean your dog will never develop cardiomyopathy. However, there are several compelling reasons why you should still consider Holtering your dogs.

First, several cardiologists who have studied Boxer cardiomyopathy feel that this test is our current best option for identifying dogs with the disease. If you test a dog and it DOES show a large number of abnormal beats (even if you have not actually observed overt symptoms of BCM) then a cardiologist may conclude that the dog is affected by the disease. Remember, the first "symptom" often observed to identify an affected Boxer is its sudden and unexpected death! By screening your dogs regularly (annually for stud dogs, and prior to each breeding for bitches) you increase the likelihood that you will identify affected dogs in time to reduce their impact on your breeding program, and on the breed as a whole. While an imperfect test may not seem worthwhile, similar testing methods have worked well to help reduce the incidence of health problems in other breeds. For example, in such breeds as the Labrador Retriever, the Collie breeds, and the Cardigan Welsh Corgi, the incidence of progressive retinal atrophy (PRA) has been reduced by breeders’ voluntary, annual CERF certification of breeding animals.

A second good reason to Holter is that breeders, and the data they can provide, are a valuable resource in the effort to learn more about BCM. We do not know enough about the ways BCM differs from cardiomyopathy in other breeds. We know very little about the way the disease progresses through the lifetime of an affected dog. We do not understand the mode of inheritance of the disease. We do not know which treatments are most effective. All Boxer breeders would like to have a better understanding of these questions, but researchers cannot get the data they need to address our concerns unless breeders are willing to do their part and volunteer their dogs as research participants.

A third reason to Holter is that the identification of living, BCM-affected dogs is vital to the development of a genetic marker test for the disease. Once affected and unaffected dogs are identified, researchers can search for DNA regions that are found only in the affected dogs. In the Cardigan Welsh Corgi, for example, a genetic marker test for PRA was very recently developed using this technology. Now, breeders can simply obtain blood or tissue samples from very young puppies, and at minimal cost can determine whether a dog will ever develop the disease. The imperfect test (CERF certification) was critical in the identification of affected animals, and in the development of the accurate early-detection system now available to all CWC breeders. It is hoped that researchers will someday be able to develop a genetic marker test for BCM, but this is going to require a great deal of breeder participation. If more Boxer breeders Holter their dogs, and volunteer their affected AND unaffected dogs for genetic studies (as simple as providing a small blood sample and a confidential pedigree), this will facilitate the development of a sophisticated test, which could make the complete elimination of BCM a possibility for the future of the breed!

A final compelling reason to Holter is that more and more breeders and puppy buyers are actively seeking Boxers from Holtered stock. Boxer fanciers who have experienced the heartbreaking loss of a young Boxer to BCM are especially enthusiastic to locate breeders who are using the most sensitive test available to screen for this disease.

The echocardiogram examines the heart for structural and flow abnormalities, while cardiomyopathy in Boxers is a disorder of the electrical conduction mechanisms in the heart muscle. An echocardiogram, performed after the age of one year, CAN rule out sub-aortic stenosis (another serious heart ailment which can affect Boxers), so it is important to perform this test. However, many Boxers that have cardiomyopathy show no abnormal signs at all on echocardiogram, so the echocardiogram is not an acceptable test for cardiomyopathy.

Many people still use routine ECGs to test for electrical conduction abnormalities of the Boxer heart. However, because the ECGs routinely used for screening are so brief (5-10 minutes), and because the arrhythmias seen in affected Boxers tend to be clustered in "runs," it is very easy for an affected Boxer to score a perfectly clear ECG. By extending the testing period to 24 hours, the Holter monitor captures a much more complete picture of the electrical activity of your Boxer’s heart, and obviously has a much higher likelihood of successfully identifying dogs that exhibit abnormalities. Before Holter testing was widely available, a routine ECG was the best test available for the identification of Boxers with cardiac conduction disorders. Now that more and more "ECG Clear" Boxers are being Holtered, we can see that the routine ECG is a far inferior test, and that it fails to identify many affected dogs.

The cost of renting a monitor is generally around $20 per dog, plus an additional one-time shipping fee (regardless of how many dogs you test while you have the monitor). If you have your vet attach the monitor to the dog (and draw a blood sample) there may be a nominal office visit fee. If you explain that you are participating in a research study, many vets will perform these services at reduced cost, and some will waive their fee entirely. Many breeders find the process so straightforward that they simply attach the monitor to their own dog, following the instructions provided. Once the test is complete, the analysis of the Holter tape may be available for no cost, or for a small fee. Many breeders who have begun using the Holter monitor report that it costs them no more than what they had been spending on annual ECGs. The cost of the test (in both money and time) may be completely offset by foregoing just a single show each year.

Your general veterinarian is not as familiar with Boxer cardiomyopathy as the cardiologists who have recommended the use of the Holter as a screening test. The veterinarians who do advocate use of the Holter monitor are cardiology specialists, many of whom have dedicated years of research to the study of Boxer cardiomyopathy. You can refer your veterinarian to one of these specialists for more information.

While longevity is a good thing to have in a pedigree, it is no guarantee. The mechanism of inheritance of cardiomyopathy is not currently understood, although it is clear that the disease has a hereditary component. Many genetic disorders can skip one or several generations before being manifested again. Boxers that have cardiomyopathy are often as active, outgoing, and boisterous as their unaffected peers, and often the first "symptom" of the disease is the sudden death of a dog that had appeared to be perfectly healthy. These sudden deaths are frequently attributed to heat stroke, bee stings, poisoning, or other such accidental causes. You may have an affected dog in your pedigree and simply not know it due to misdiagnosis of the dog’s cause of death. Even if your foundation were unaffected, any outcross you have ever performed may have introduced the genes that are associated with cardiomyopathy. If your dogs are truly free of cardiomyopathy, then Holtering them regularly throughout their lifetimes will simply help to demonstrate this fact. These dogs could also be very valuable as participants in studies designed to identify the genetic markers of the disease!

The vast majority of veterinarians in general practice have never performed this test, but the instructions that are provided with the monitor are very straightforward and explicit. For some models of Holter monitors, helpful websites are available which provide written descriptions of the procedure, with photographs to illustrate each step. There may be a breeder in your area who has experience with the Holter test. These folks can be a great help when you are using the monitor for the first time. However, many novice Holter testers have successfully managed to set up tests in their own homes, with only the written instructions to help them. Once you have walked through the procedure with the first dog, you will find that it goes much more quickly, and seems much simpler, as you repeat the test on your other dogs.

10. What if I Holter my dog and I get bad news?