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Friday, July 15, 2011

Holter Monitoring for Boxer Dogs

Boxer breeders who are concerned about producing long-lived, healthy puppies engage in health testing, which includes, among other things, holter monitoring. A holter monitor is a 24-hour ambulatory EKG, meaning the dog wears the monitor for 24 hours while it goes about its normal daily routine -- usually. (Some dogs dislike the holter and won't do things like walk, potty, play, etc., but most, especially after the first time they wear it, adapt quickly and act normally.) Holtering detects abnormal heartbeats, called VPCs (ventricular premature contractions) associated with Arrhythmogenic Right Ventricular Cardiomyopathy, or ARVC, a leading health issue in Boxers today.

Holtering is not a one-time deal -- a "clear" holter simply means the dog is not displaying symptoms of ARVC on that day. Research suggests that the number of VPCs varies by as much as 80% on a day-to-day basis, and ARVC is generally a later-onset condition, first appearing at 6 years or older. Due to these, one clear holter at any age does not provide a lifetime clearance for the dog. Although a DNA test has been developed that detects one mutation associated with ARVC in some Boxers, it is likely that there are other genes also involved and so a "Negative" ARVC-1 DNA test result does not negate the need to annually holter breeding dogs.

The American Boxer Club recommends annual holtering for dogs in breeding programs, beginning at 12 months of age. Though Dr. Kathryn Meurs, the lead researcher on ARVC in North American Boxers, has stated that ARVC is unlikely in a Boxer younger than 3 years of age, sufficient dogs have been diagnosed and/or died at younger ages to warrant continued holtering even in young dogs. Additionally, holtering can provide baseline data to compare with future reports, and can detect other abnormalities in the heart's rhythm.

Owners of dogs diagnosed with ARVC also holter their dogs routinely, sometimes as often as every three to six months, depending on the severity of the condition or when medication dosages are being evaluated. Some concerned pet owners may holter their dogs, to perhaps detect a problem before symptoms occur. (Unfortunately, in some cases the first sign of ARVC is that the dog drops dead; however with regular holtering by conscientious breeders in the last two decades, the occurrence of those situations -- in those breeders' dogs -- has decreased.)

Regardless of the reasons for holtering -- pre-breeding screening, keeping tabs on an existing problem, or peace of mind -- Boxer owners who engage in repeated testing would do well to learn to hook up the monitors themselves. Renting a monitor from a cardiologist, and having them hook up the equipment, is the most expensive method of holtering. Many Boxer breeders, and a handful of Boxer clubs, offer their monitors for rental, generally for a much lower cost than a cardiologist, and if they're local some will help with the hook-up. Owners of multiple dogs would probably be better off purchasing a monitor of their own, or in conjunction with another owner or two; in the long run the purchase cost will be less than the cost of renting the holter every time.

Analog holter monitor
Holter monitors can be either analog, recorded on a cassette tape, or digital. Analog monitors are available to purchase as refurbished units; they are larger than digital monitors but about 1/3 of the cost. Digital monitors are about the size of a pager and the recording can be transmitted via telephone or Internet, rather than mailing in a cassette tape. The cost of reading the recording is the same regardless of the monitor used. The software for digital holter monitors is proprietary, so recordings must be read by the same company that provided the monitor. Cassette tapes from analog monitors can be read by any company that processes the tapes.

Recordings are decoded by machine, and then scanned by certified technicians to evaluate abnormalities and determine whether they are truly arrhythmias or simply artifact, abnormal readings due to the dog's actions such as rubbing, bumping, or coughing. Some services offer only machine readings -- this is less than ideal, since there is a possibility of an artificially inflated number of VPCs due to artifact. A cardiologist's interpretation of holter results is also available in many cases, for an additional fee; this is probably not necessary for pre-breeding screening.

Holtering is an essential, if nerve-wracking, part of a Boxer breeder's health-testing process. The few seconds waiting for an e-mailed holter report to open is agonizing, but the long-term benefit to the breed by detecting clearly affected dogs and removing them from breeding is worth the short-term stress. Even if faced with the heartache of a promising dog that fails a holter, knowing the dog has VPCs will allow the breeder to monitor its condition and, if necessary, start medication, which can be quite successful in allowing the dog to live a mostly normal life in both quality and length.