Subaortic Stenosis

Subaortic stenosis (SAS) is a genetic and congenital heart condition of dogs, meaning that it is present at birth and it can be inherited. Several breeds can be affected including the Golden Retriever. The condition is usually detected during puppy vaccine visits to the veterinarian by hearing a heart murmur during physical examination. A heart murmur is the abnormal sound of blood rushing through one of the heart valves. Instead of just the heart beat, a whistle of blood flow through a narrowed opening is heard. The puppy will most likely appear normal in all other respects. There is a possibility that the murmur may come and go, or it may develop slowly; therefore, it is important to check a puppy's heart condition often during the first few months of age. This is a very frustrating condition to be identified in your pet because the future is bleak and the chance for long term survival is low. These dogs will either go into heart failure or they will die suddenly, essentially from a severe heart attack.

A little review of normal heart function and circulation is in order to understand what SAS is and why it is so devastating. As you may remember from high school science, the heart has four chambers; the right atrium, the right ventricle, the left atrium, and the left ventricle. You can picture these as four circles together with two on the top and two on the bottom. The atria make up the top of the heart and receive blood from veins and the ventricles make up the bottom of the heart and pump blood into the arteries. Blood from most of the body is returned to the right atrium by veins, it passes down into the right ventricle, and is then pumped to the lungs where it receives oxygen. The veins of the lungs return blood to the left atrium and it passes into the left ventricle. There are valves or gates at each of these junctions throughout the heart and the aortic valve is between the left ventricle and the aorta, which is the main artery exiting the heart carrying oxygenated blood to the body. Subaortic stenosis is a narrowing of the left ventricular chamber just below the aortic valve. This creates problems for the heart because instead of just having a gate to open and close when blood is pumped out, there is a narrow canal almost like a funnel below the valve that makes the heart work harder to push the blood out of the left ventricle and into the aorta. When the heart has to work harder, the heart muscle responds by thickening. As the muscle wall thickens the chamber size can shrink in comparison decreasing the amount of blood that the left ventricle can handle. The thickened heart muscle also demands more oxygen to work. The blood vessels that supply the heart muscle with oxygen, the coronary arteries, are squeezed out by the thickness of the muscle and can't carry enough blood to the heart muscle. This can lead to muscle tissue of the heart dying as in a heart attack. The area of the left ventricle that is narrowed below the aortic valve also can develop scar tissue due to the force of blood through this area. The scar tissue narrows the canal more and decreases the flexibility of this area.

As mentioned before, the two potential outcomes of SAS are heart failure and sudden death. Changes take place in the heart because of the narrowed aortic canal. The heart works harder, the wall of the heart muscle thickens, the chamber size decreases, and the amount of blood the ventricle can handle decreases. Heart failure often occurs when the heart can not get enough blood in and out to keep up with demand. Blood backs up behind the left side of the heart in the lungs and causes congestion. The dog shows this congestion by coughing, weakness, tiring easily, and possibly fainting. Sudden death is just what it sounds like, the dog will die without giving us any clue that something is wrong. What probably happens to cause this sudden death is that a blood clot severely disrupts circulation to the heart muscle and it dies or the heart rhythm is changed dramatically and suddenly so the heart doesn't function and just stops.

What can you do if your puppy is diagnosed with a heart murmur consistent with SAS? First of all, contact your breeder if you can to let them know. They will not want to use this same set of parents to breed again. The puppies and dogs affected with SAS can be evaluated and classified as mild, moderate, or severe. Tests such as chest X-rays, echocardiography, and electro-cardiography can be performed to evaluate the severity of the situation. Unfortunately, not much can be done to treat the condition. A balloon catheter can be used in an attempt to dilate the narrowed aortic canal but the canal soon narrows again. If your dog with SAS develops heart failure, medications can be prescribed to alleviate the clinical signs it is experiencing. You can not prepare yourself for the sudden death of your pet. Even if you know that it is a possibility with SAS, it is still a shock when it occurs.

by Anita R. Weidinger, D.V.M. used with permission

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