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;
- Normal-congenital heart disease not evident,
- Equivocal-congenital heart disease cannot be diagnosed nor excluded
- 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