Cardiomyopathy Update Printed November/December 08
Reproduced by kind permission of the Claymore and Author: Betty Stephenson, D.V.M.
I have been asked to discuss briefly what advances have taken place in the realm of Scottish Deerhound cardiomyopathy in the last year and will outline for you what I have been involved in in that field. You may be aware that cardiomyopathy takes many forms and to date, several distinct types have been identified with advances in determining the genetic bases for Doberman and Boxer DCM, but no genetic tests having been developed as yet. If Deerhounds share one of these types, we will benefit from the studies funded by those interest groups. That’s a long shot, however. The take-home message from last year’s AKC Canine Health Conference was, for me, that the recently completed “Relatedness of Breeds” study has assigned each breed to a place near the other breeds most closely related to it. Some of the proximities are quite surprising. This means to us, that research designed to discover the genetic basis of diseases in breeds closely related to ours will very likely discover it for ours. That is, we can pool our resources with breeds like the Irish wolfhound and gain much in funds and genetic material that could put us over the edge in instances where we are limited by numbers, all instances in our case! Wolfhounds have it over us in numbers in spades. While I believe that the introduction of mastiff breeds to the Scottish Deerhound in order to create the IW may have added some unique types of DCM, the two breeds fall almost together in the study. It will be greatly to our interest to combine our resources, in this effort and in others.
We are sorely limited in our ability to cooperate in studies, however, by our difficulty in detecting cardiomyopathy sometimes before it kills our dogs. One, echo clinics are costly and difficult to organize and attract participants, and two, some of the information gleaned from the one I hosted last November has been perplexing. First let me say that I believe volunteers in each region should try to put together clinics yearly and have their own dogs echo’d regularly (the club recommends every two years). I did this and can help others plan their own. After the first time, the logistics should prove easier. The operator needs to be aware of the “normal parameters” complied by Dr. Phil Fox (and others) who have performed controlled studies on numerous Deerhounds. We will be able to identify some asymptomatic animals in this manner.
I put together the clinic last November with a cardiologist who shares an interest with me in utilizing the new cardiac blood test, the pro-BNP, as a screening test for breeding stock. This is a peptide detectable in the blood which rises in response to stretching of the left ventricle of the heart, and so may be elevated before the symptoms of cardiomyopathy become apparent. It has other clinical uses, which are driving its development in veterinary medicine, but it could become a very valuable tool for us as breeders if we can establish a normal range for Deerhounds and prove it is reasonably reliable. It could be both more sensitive and much cheaper and easier that an echo clinic. The company developing the test is interested in cooperating with us in this endeavour.
In the spring of 2007, I tested about 25 Scottish Deerhounds for BNP levels and found nearly all of them to be above the (then) established normal range. Some were way above. The company wanted cardiac echoes performed on all these dogs to confirm occult DCM (or disprove it, thus rendering the test useless for the purpose for which we were hoping to use it). Most of the dogs I had tested and several others participated in the November clinic, and surprising results were compiled: only two dogs had abnormal echoes, one of which was over 12 years old and the other one of the few animals to have a BNP in the “normal” range. They are both asymptomatic today. For the animals with the highest BNPs, the plan is to run Holter monitors and see if arrhythmias are present. I have always believed that in our breed, at least one form of cardiomyopathy presents as strings of arrhythmias that may kill the dog the first time they occur, but it’s much more likely that arrhythmias exist before the fatal episode. This is true of Dobermans and Boxers. We performed the Holter monitor (24-hour electrocardiogram monitoring with a mobile ECG monitor) on the dog with the highest BNP and normal echo, and he did have numerous arrhythmias. Knowing this allows us to begin cardiac medication before clinical signs develop and lengthening asymptomatic life, as well as giving us more information to use in our breeding programs. Boxer and Doberman breeders buy Holter monitors to share amongst themselves and use the test on a yearly basis to detect DCM early. While echocardiograms are the gold standard today, tomorrow we may find them not sensitive enough to detect DCM in Deerhounds early enough to be much use in many cases. They do, however, pick up some cases that other tests like the pro-BNP do not, and they provide other essential information in the characterization of the disease. So until all the information is in, supporting cardiac clinics is critically important. Perhaps having blood draws in conjunction with them will yield useful information in the pursuit of more sensitive (and convenient) testing procedures. Idexx Labs has purchased the pro-BNP technology, and I am working with them to develop the use we are interested in. Holter monitoring may also be the screening test of the future, but until more of these are done in conjunction with both echo clinics and pro-BNPs, we won’t have all the pieces to the puzzle. And until we can accurately diagnose asymptomatic DCM, we cannot even begin to find the genetic causes.
(There are at least four studies currently being funded by the AKC CHF, two of them involved with identifying the genetic causes of cardiomyopathy in giant breed dogs.)
Betty Stephenson. D.V.M.