Subaortic stenosis is a narrowing (stenosis) of the area underneath, the aortic valve, that causes some degree of obstruction or blockage of the blood flow through the heart. The narrowing can be mild, moderate, or severe; if moderate or severe, it can force the heart to work harder and potentially be harmful to the heart's health.
Subaortic stenosis is a problem that affects dogs and is rare in cats. It most commonly occurs in large-breed dogs. Subaortic stenosis appears to be genetic in origin; the first signs of it may be present at birth (moderate or severe cases) or may appear in the first year of life (usually milder cases).
In mild sub-aortic stenosis no signs are observed. In moderate (sometimes) and severe (almost always) cases, symptoms such as weakness, breathing difficulty (dyspnea), fainting (syncope), and, in extreme cases, sudden death are all possible as a result of subaortic stenosis. Realize that dogs with subaortic stenosis, even severe subaortic stenosis, may look perfectly healthy and active. These dogs generally do not realize that their hearts are compromised.
Your veterinarian will perform a thorough physical examination (including listening carefully with a stethoscope for a heart murmur or irregular heartbeat) and ask you whether you have seen any of the symptoms described above.
- Chest x-rays are useful if symptoms such as labored breathing are present because dogs can develop labored breathing for many reasons, not just subaortic stenosis. Chest x-rays can show the telltale signs, such as fluid accumulation in the lung tissue in severe cases.
- An electrocardiogram (ECG) depicts the pattern of electrical activity in the heart and any irregularities in the heart’s rhythm (arrhythmias).
- An echocardiogram (cardiac ultrasound) is the test of choice for subaortic stenosis. An image of the inside of the heart is displayed on a monitor in real time. This test allows the veterinarian to assess the valves (including any narrowing), blood flow patterns and velocity, degree of stenosis (i.e., extent of blockage), and other aspects of cardiac structure and function. The degree of severity is assessed using several components of the ultrasound exam, especially Doppler ultrasound, which measures the direction and flow of blood as it courses through the heart.
Mild subaortic stenosis is of no consequence to an individual dog and it is usually recommended that the dos not be bred. Moderate or severe subaortic stenosis may cause symptoms and may increase the risk of sudden death. Depending on the exact degree of severity, treatment may be required, and other measures (such as limiting activity) may be recommended to minimize the amount of work done by the heart. There is no cure for subaortic stenosis. Since it is thought to be of genetic origin it is often recommended that dogs with subaortic stenosis not be bred to avoid passing the disease along to future generations.
If the disease is mild, treatment is not required. However, subaortic stenosis can get worse as a growing dog reaches its adult age and body size. Therefore, dogs with moderate or severe subaortic stenosis, may require medication. The most common form of treatment is a medication given orally called βeta blockers, which reduce the intensity of the heart's work, help to prevent the heart from beating too fast and can control arrhythmias. If your dog has been found to have moderate or severe subaortic stenosis, it is important to reduce the workload on the heart (and therefore to decrease the risk of sudden, collapse, fainting, or even sudden death) by controlling or avoiding bursts of sudden activity or any intense exertion.
Several surgical procedures and minimally invasive (balloon catheterization) procedures have been performed to reduce the obstruction of subaortic stenosis with variable success. However, recently a new technique has become available utilizing a special "cutting" balloon, which appears to have favorable results.
FOLLOW UP EXAMINATIONS:
Follow-up appointments are important to monitor progress, to determine if treatment should be adjusted, and to keep your pet as comfortable as possible. If placed on medication, periodic echocardiograms may be performed to help tailor the therapy to your pet. If your dog has difficulty breathing or collapses, go to your veterinarian or the local veterinary emergency clinic immediately, even if the collapse is brief and your dog is back on his or her feet shortly.