Tuesday, March 6, 2012

How Many VPCs Are Too Many VPCs?

In the last BU Blog, I related a conversation I’d had with my cardiologist in which we discussed how frustrating it was for Boxer breeders to have one board certified veterinary cardiologist clear a dog of SAS with a flow rate of 2.21 m/s…and another equally qualified cardiologist grade the same dog with exactly the same flow rate as “equivocal.”

Alas – the upshot of that conversation was that although cardiologists all agree about grading very low flow rates (e.g. 1.2 m/s) and very high flow rates (e.g. 3.0 m/s), none of them can say for sure what the ranges in the middle mean in terms of SAS, if the dog doesn’t have any other sign of the disease, such as a fibrous ridge in the aorta or a turbulent blood flow.  

So we concluded the blog by saying that diagnosing SAS seems to be another area in which there’s a lack of black and white guidelines on Boxer heart disease; and another reason for breeders to try to get comfortable with using our own best judgment along with the opinions of the professionals when making decisions about our own breeding programs.

More recently, Boxer breeders have been expressing their frustration at the lack of guidelines to help us navigate through an even murkier gray area of Boxer heart disease – ARVC and the VPCs (Ventricular Premature Contractions) that often indicate the presence of cardiomyopathy in an individual boxer. Those breeders are saying, some of them in so many words, that since the ABC website provides us with guidelines on a range of flow rates that clear our dogs of SAS, why doesn’t the ABC publish guidelines that tell us how many VPCs it’s acceptable for our dogs to have at different ages?

Well for one thing, the ABC is not a medical research institution and the SAS flow-rate guidelines that appear on the ABC website represent the opinion of only one cardiologist with whom the leaders of the ABC Health & Research Committee happen to agree. What’s more, there’s a difference of opinion among cardiologists on those “ABC guidelines,” because they do not conform to the standards set by the ACVIM (American College of Veterinary Internal Medicine) for American board-certified veterinary cardiologists.

But back to ARVC and VPCs:

At the present time, the only absolutely surefire way a cardiologist can tell whether a non-symptomatic dog has BCM/ARVC is by doing a necropsy. And unfortunately, at that point the dog is dead and the question is academic, except perhaps for the owners of the dog’s offspring.

Of course, a reliable DNA test would also tell us whether a dog had the mutant gene(s) that causes ARVC and was therefore likely to develop the disease and reproduce it. But the ARVC-1 test has not lived up to its initial promise, and so we’re back to where we were before Dr Meurs made her announcement in April 2009 – holtering our breeding stock regularly and trying to figure out how many VPCs are too many VPCs. And the sad fact is that we don’t have any better an understanding of exactly what that number is now than when the late Wendy Wallner, DVM, proposed a set of very broad guidelines for Boxer Cardiomyopathy in an article on Boxer heart disease she wrote for the April 1999 issue of The Boxer Underground.

As chair of the ABC Boxer Health & Research Committee and a member of the board of the American Boxer Charitable Foundation (ABCF), Wendy devoted her tragically brief life to the cause of Boxer health and led the fight against what we then knew as Boxer Cardiomyopathy (BCM).  A read of the entire article at http://www.boxerunderground.com/apr_bu_99/dr.htm will give newcomers to the breed a good idea of what we were up against in 1995 when the ABCF was founded and the ABC membership voted in a survey to make BCM research a priority for our new foundation. In the meantime, based on experience and observation, I firmly believe the fact that breeders have been following the guidelines in the excerpt printed below has led to our seeing fewer Boxers suddenly “just drop dead” at 3, 4, and 5 years of age. RIP Wendy – your work continues.
“A few years ago, upon my appointment to the ABC's Health and Research Committee, I came up with a protocol for heart testing for boxers. These guidelines were published in the ABC News Bulletin in December of 1996. The recommendations were as follows:
“Minimum Heart Screening for boxers involved in breeding programs and/or performance events:
Age 1 year: auscultation by a board certified veterinary cardiologist (If arrhythmia detected - Holter exam; if murmur detected - Echocardiogram) 
Rationale: One year is the accepted time for clearance of sub-aortic stenosis. This auscultation screening could be performed at the national specialty and at individual breed club's specialty shows for a nominal fee. Any dogs with murmurs would be referred to a cardiologist in their area for further workup.
“Age 2 years: Holter monitor, auscultation (Echo if murmur detected)
Rationale: The 2-year check would occur before the animal was used for breeding (at least extensively) and would be useful in detecting dogs with early arrhythmias before they are bred. In some dogs, arrhythmias have been detected as early as 12 weeks of age.
“Age 5 years: Holter monitor, auscultation (Echo if murmur detected)
Rationale: By 5 years, many animals would show signs of arrhythmia if they were going to develop CM, since the arrhythmia often precedes clinical disease by several years.
“The main purpose of these screens was to develop a database which could be analyzed and related to causes of death in dogs so that some sort of standardized system of interpreting the holter results could be determined. Not only would it help to identify and eliminate dogs with SAS from breeding programs, it would also help identify and eliminate those asymptomatic boxers with very large numbers of VPCs. It was never intended to eliminate any and all dogs with VPCs from breeding programs. There simply is not enough information available to use the results in this manner. If large numbers of boxers are not holtered and followed over time, there never will be a database large enough to provide meaningful holter results. If this is the case, we are at the mercy of the only other test that will identify boxer CM - a genetic marker for the disease. Unfortunately, this type of test can take decades to establish. Since we know that the hallmark of boxer CM is arrhythmia and that the Holter is the best tool to detect arrhythmia, it is the only method we currently have to try to evaluate our breeding stock before they have produced offspring. While there currently are no concrete numbers to identify normal vs. abnormal dogs, the Holter is still extremely important in identifying those grossly abnormal dogs with hundreds or thousands of VPCs who are asymptomatic and would otherwise be unknowingly reproduced. Until many Holtered dogs have been followed into old age and their medical histories analyzed and causes of death determined, we will not know the true significance of lower numbers of VPCs. We can, however, use all information obtained through Holter testing responsibly by slanting a breeding program toward those boxers that seem less affected.”
NEWS FLASH!!!  The Drawbridge Inn in Ft Mitchell, KY – the site of the 2012 ABC National Specialty – was sold this morning (March 6) to the mortgage holder, who intends to keep the property open as a hotel and start making major improvements. Kudos to ABC President Salli Moore-Kottas, who stayed on top of this situation as it developed and was prepared to proceed with a "Plan B" if the sale had not ended favorably.  Now...on with the show!!! 

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