What is Aortic/Subaortic Valvular Stenosis: AS/SAS ?
A dog’s heart has four chambers. The top chambers are called the atria and the bottom chambers are called the ventricles. Valves separate the atria from the ventricles on both sides of the heart. Valves also separate the right ventricle from the main artery to the lungs (the pulmonary artery) and the left ventricle from the aorta (the main artery to the body). The word “stenosis” means “narrowing,” and aortic stenosis describes a narrowing along the aorta as it leads out of the heart. It is typically present at birth and worsens over the first year of life. Clinical signs of heart disease can occur at any age and depend upon the severity of the obstruction of blood flow out of the heart and into the aorta. The defect can occur above the valve, just inside the aorta, at the valve itself, or below the valve, closer to the heart itself. A heart ultrasound (or echocardiogram) is an important way to see what is happening with the heart and surrounding blood vessels.
Are there some breeds of dog that are more susceptible to aortic stenosis?There are several dog breeds in which there are risk factors for aortic stenosis. These include:
Newfoundland
German Shepherd Dog
Golden Retriever
Bouvier des Flandres
Rottweiler
Boxer
Samoyed
English Bulldog
Great Dane
Bull Terrier
What are the clinical signs associated with aortic stenosis?The signs of aortic stenosis are related to the severity of the narrowing, and range from no signs at all, to congestive heart failure, fainting, or sudden death. A heart murmur may not be present in very young puppies, but then will develop over the first 6 months of life. Sometimes the murmur is dramatic enough that, by placing a hand against the chest wall, it is possible to feel a vibration caused by the turbulence of the blood flow. As heart failure progresses, the dog may develop rapid breathing or difficulty breathing, and will develop exercise intolerance. Even the pulses in the major arteries may be affected. Most of the time, aortic stenosis is a developmental problem that is present at birth, although it can also occur secondary to infection of the lining of the heart (endocarditis). Endocarditis is more likely in dogs with a suppressed immune system, bacteria in the blood, a generalized infection, or abnormal blood flow through the heart.
Is there any treatment for aortic stenosis? Treatment focuses on managing the symptoms of congestive heart failure, irregular heartbeats, and fainting episodes. Activity may need to be restricted in order to prevent fainting or collapse. In dogs who are severely affected, exertion can be fatal, so these are dogs who need extra supervision. A low-sodium diet may be in order. Your veterinarian can guide your feeding choices. Theoretically, definitive treatment would require open-heart surgery with heart-lung bypass to repair or replace the valve, but the risks of this surgery for dogs with aortic stenosis currently outweigh the possible benefits. Dilating the narrowed aorta using an expandable balloon via heart catheterization may improve clinical signs in some dogs. "Medical management treats clinical signs but is not a cure."Medical management treats clinical signs but is not a cure. There are several classes of medication from which your veterinarian may choose including beta blockers and calcium channel blockers. Your veterinarian may recommend periodic monitoring. This could include electrocardiogram to evaluate the electrical activity in the heart, chest x-rays to assess changes in heart size and shape, and/or echocardiogram.
One of the most common heart defects occurring in dogs, boxers in particular, is aortic or subaortic stenosis. In most cases the stenosis, or narrowing, is produced by a fibrous ring of tissue below the aortic valve, hence the term "subaortic." The disease is inherited but its mode of transmission is not known at this time. Oxygen-rich blood flows from the left ventricle of the heart, through the aortic valve and into the aorta, which transports the oxygenated blood to all organs and tissues in the body except the lungs. Narrowing of the aortic valve requires the left ventricle to work harder to pump the necessary amount of blood. This increased workload can result in hypertrophy (thickening) of the left heart muscle. Since the blood is being forced through a smaller-than-normal opening, there is also increased pressure generated by the pumping action of the heart. This increase in pressure can cause dilation (ballooning) of the aorta. Reduced flow can produce symptoms of fainting (syncope) and even sudden death, although abnormal heart rhythms (arrhythmias) may also contribute to these symptoms. The stenosis creates a change in the flow of blood through the valve causing turbulence which results in swishing sound called a heart murmur. Often the stenosis can be seen on echocardiography. Murmurs are graded from one to six, but a weak murmur may not always be detectable, even by a trained cardiologist. Exercising the dog during the cardiac exam may increase detection of murmurs in some cases. Not all murmurs are the result of aortic stenosis/subaortic stenosis, but may be so-called "innocent," or physiologic murmurs, particularly when they occur in young animals. The diagnosis of AS/SAS is best made by a veterinary cardiologist, or one with equivalent experience and training. When a murmur is identified and not presumed to be physiologic, further investigation is warranted. The least invasive and most available testing consists of Echo/Doppler.This testing is best performed when the animal is full grown or at least one year of age, unless the dog is experiencing symptoms of heart disease, in which case testing should be pursued promptly. As in many instances in medicine, these tests have limitations and are not perfect. False positive and false negative diagnoses may occur. In some cases this is simply because the abnormality is too subtle to be diagnosed with currently available knowledge and/or technology. Echo-Doppler flow rates can vary considerably in the same animal depending on the proficiency of the operator and the amount of stress to which the animal is subjected. These limitations may be minimized in part by examiners with advanced training using the appropriate ultrasound equipment, techniques, and standards established by the American College of Veterinary Internal Medicine, Specialty of Cardiology.