Health corner: Inherited Cardiac Problems
By Sharon Schaefer
This has been the most challenging title to research to date. Two different heart defects have been reported so far in Iceland Sheepdogs. One is a valve condition present at an early age (probably aortic stenosis) while the other is a cardiomyopathy developing later. I don’t believe that these are just one condition manifesting differently but this is a possibility.
However as OFA has eight ‘murmur-producing’ congenital heart diseases in its descriptive chart for veterinarian specialists, and cardiomyopathy itself is divided into at least four different types (the most common is dilated cardiomyopathy), creating a useful tool for Icelandic fanciers is difficult. Then we add in ‘innocent murmurs’, which should disappear by 6 months of age (there is some belief innocent murmurs may also occur in very athletic dogs).
Technically, cardiomyopathy is an acquired heart disease, not a congenital heart defect and so it does not appear in some lists. However, it is the second most common cause of heart disease in dogs and as the different types of cardiomyopathy occur very frequently in some breeds and almost never in others there must be a genetic predisposition. In humans it is most commonly a genetic mutation. In dogs, this fatal condition usually does not show up until at least 6 years of age when they have already passed it on to puppies. There are studies of Boxers, Dobermans, and Great Danes right now looking for a genetic marker in each of those breeds but whether this will be useful for other breeds is not known.
Even when checked by an A.V.M.A. board certified specialist in cardiology some heart conditions cannot be clearly identified and a few cases not even found. Beginning with a very quiet, careful physical heart examination by a cardiologist provides the most reliable diagnosis. The dog may not be panting, accompanied by a whining sibling, or a chatty owner! If Congenital Heart Disease is suspected then use by a trained specialist of an echocardiograph including pulsed or continuous wave Doppler on top of the physical listening should find all but a very tiny minority of problems. This is also how innocent murmurs are determined. This is a noninvasive procedure but it is expensive and as most heart diseases are progressive it is only valid for a short time. OFA will only accept results from dogs over 12 months of age for its database at a fee of $15.
They have the following warning in their material "At this time inherited, developmental cardiac diseases like sub aortic stenosis and cardiomyopathies are difficult to monitor since there is no clear cut distinction between normal and abnormal. The OFA will modify the congenital cardiac database when a proven diagnostic modality and normal parameters by breed are established. However at this time, the OFA cardiac database should not be considered as a screening tool for these diseases."
In some European countries specific breeds with hereditary heart problems can only register puppies from dogs with a clear cardiac certificate in the previous 12 months just as we recommend annual CERF exams. Heart murmurs are graded by specialists on a scale of 1–a very soft murmur, 2-a soft murmur readily evident, through to 6-audible even when the stethoscope is lifted from the thoracic wall.
The Canine Inherited Disorders Database at Atlantic Veterinary College UPEI has the longest list - twelve hereditary heart conditions in dogs. Four of them can occur individually or in a grouping, which then is named the twelfth condition – tetralogy of Fallot. More recent human studies are suggesting a probable relationship even when only one of the four presents as a disease.
Two studies in dogs have tracked the rate of different hereditary heart defects. The most common, aortic stenosis creates a third of all murmurs. In descending order the others are pulmonic stenosis – a fifth, ventricular septal defect, patent ductus arteriosus, mitral valve dysplasia, tricuspid valve dysplasia, endocardial fibroelastosis, and tetralogy of Fallot with the final two being very rare. In its mildest forms, aortic stenosis creates no problems and the dog will live a normal life. Unfortunately using this dog for breeding is not recommended. The recommendation is that any dog with any of the conditions discussed in this article is not a candidate for breeding.
www.americanboxerclub.org/genetic_diseases.html
www.gdca.org
http://www.morrisanimalfoundation.org/learn/animals/dogs/QAheartdisease.asp
http://www.offa.org/
www.pubmedcentral.nih.gov Search: dog/canine heart/cardiovascular congenital
http://www.steynmere.com/AORTIC_STENOSIS5.html
www.upei.ca/~cidd/intro.htm
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