Aortic stenosis(AS) had been reported to be the third most prevalent
congenital cardiac disorder in the dog, but researchers at the
Ontario Veterinary College (Dr. Michael O'Grady Dip-ACVIM Cardiology
and staff) have found it to be the most common congenital cardiac
disorder in dogs they have examined. It is reported to be the most
common congenital cardiac disorder in Rottweilers.
Aortic stenosis is characterized by a narrowing of the aortic valve,
the outflow tract from the heart's left ventricle. This causes a
partial obstruction of blood flow into the circulation, increasing
the heart's workload and in turn causing an increase in the thickness
of the left ventricular wall. This "left ventricular concentric
hypertrophy" results in decreaed left ventricular distensibility
and an increase in heart dysrhythmias. Aortic stenosis may be
subvalvular, valvular or supravalvular, depending on where the
constriction is located. Subvalvular, or Sub Aortic Stenosis (SAS) is
most common.
Most commonly, puppies are presented to a veterinarian for their
first series of vaccinations and a heart murmur is noted as an
incidental finding, as the affected puppy is without clinical
symptoms of cardiac disease. However, in severe cases, syncope
(fainting) or sudden death may occur. For those of you who may be
interested, the murmur is systolic, with the Point of Maximal
Intensity (PMI) over the left heart base. The murmur presented may be
of varying intensity, from low (grade 1 or 2 out of 6) to moderate or
severe (grade 3/6 or greater). These murmurs can be confused with
"innocent", or non disease related murmurs, which usually
occur as well over the left ventricular outflow tract, are of low
intensity (grade 1/6 or 2/6) and occur early in systole (prosystole).
Innocent murmurs, however, should resolve by six months of age. Some
authors believe that similar innocent heart murmurs may also occur in
adults, particularly in large and giant breeds and/or very athletic dogs.
Research has indicated that aortic stenosis is a progressive disease,
but the rate of progression varies with maturity. In immature/growing
dogs the rate of progression is increased, while progression is
restricted to a very slow rate in mature/adult dogs. It has been
reported that if a dog with aortic stenosis lives to be greater then
three years of age, it USUALLY does not have aortic stenosis that is
severe enough to affect left ventricular performance.
Diagnosis (and most accurate prognosis) is acheived either through
Doppler echocardiography, which is a safe, non-invasive procedure or
via cardiac catheterization. On Doppler, the velocity of bloodflow
through the aorta is measured, and it has been reported that if the
bloodflow velocity is less than 4 metres/second at maturity, the dog
USUALLY will have a normal quality and quantity of life. However, if
the bloodflow velocity is measured to be greater than 5
metres/second, the dog will USUALLY succumb to the disease. These
testing procedures in our dogs are very important, as an affected
dog's electrocardiogram (EKG) is usually normal and radiographs are
frequently normal in affected dogs as well.
In order to attempt to learn more about the hereditary nature of this
disease, it is important that we all have our dogs tested by a
board-certified cardiologist prior to breeding. Although the abscence
of a heart murmur DOES NOT mean that a particular dog is not
affected, or that he/she does not carry this disease, and therefore,
the ability to pass it on to successive generations, it DOES afford
us a low cost, non-invasive screening test. The cardiologist will
listen to your dog's heart in a quiet setting at rest and then again
after exercise. Dogs who have a heart murmur are recommended to
undergo further testing, specifically Doppler echocardiography. The
Orthopedic Foundation for Animals (OFA), now has a cardiac registry
and will catagorize dogs as;
1) Normal-congenital heart disease not evident,
2) Equivocal-congenital heart disease cannot be diagnosed nor
excluded
3) Abnormal-examination indicative of congenital heart disease.
It is important that we read the ENTIRE cardiac certification number,
as the OFA is allowing non-specialist general practitioners to
certify dogs, and only by examining the entire certification number
can you differentiate between those dogs examined by a
board-certified veterinary cardiologist and those certified by a
general practitioner. The OFA certification number of a cardiologist
cleared dog will have a "C" at the end of the number
combination, while the number of a practitioner cleared dog will have
a "P". For example, O-CA123/45M/P-T would be
Rottweiler-Cardiac number 123/age 45 months/PRACTITIONER
cleared-Tatooed, whereas RO-CA123/45M/C-T would be the identical dog
with a CARDIOLOGIST cleared OFA certification number.
I, myself, have a dog that three general practitioners (including
myself!)auscultated and would have classified free of a heart murmur.
However, a board-certified veterinary cardiologist heard a soft
(grade 1-2/6) murmur upon examination and the dog has been classed
(for now) as "equivocal" by the OFA. After consulting with
this cardiologist and others, I have decided to breed this dog now
(he is 2 years old), check all resulting puppies at 6-9 months of age
and have him rechecked at 4-5 years of age (maturity). I will also
have his heart checked by a cardiologist post mortem, so the outflow
tract, chambers size, heart wall thickness, etc. can all be measured.
Will it be difficult to remove the heart of a dog I love so dearly?
YES...but I see it as a greater act of love, one last thing he (and
I) can do for this magnificent breed.
Questions/Comments/Discussion always welcome!
Dr. Cathy Priddle
