Subvalvular Aortic Stenosis In Dogs And Cats An Inherited Heart Defect Common in Large Breed Dogs

Subvalvular aortic stenosis -- or SAS -- is a heart defect that is common in dogs and rare in cats. It is characterized by a narrowing of the area underneath the heart’s aortic valve.

This narrowing -- or stenosis -- creates an obstruction that can make it difficult for the heart to pump blood into the body. In severe cases, the heart may have to work harder than usual to get the job done. SAS can have a serious effect on a pet’s heart health and can even cause sudden death.

Read on to learn the causes, symptoms, and treatments of subvalvular aortic stenosis in dogs and cats.

Causes of Subvalvular Aortic Stenosis

SAS is an inherited condition that is most often seen in large and giant breed dogs such as the Boxer, Golden Retriever, German Shepherd, German Shorthaired Pointer, Rottweiler, English Bulldog, Newfoundland, and Great Dane. Cats can also develop the condition, though cases are rare.

The heart is made up of four chambers separated by four valves that allow blood flow in one direction. In SAS, there is extra tissue below the aortic valve, which is the valve that separates the main pumping chamber of the heart from the aorta -- the main artery that delivers blood from the heart to the body.

The extra tissue below the aortic valve causes either mild, moderate, or severe narrowing, and this creates an obstruction that affects the heart’s ability to deliver blood to the body. In mild or moderate cases, the obstruction may only result in a benign heart murmur. In severe cases, it can result in congestive heart failure due to overwork, infection of the aortic valve, or sudden death due to arrhythmia (irregular heartbeat).

Symptoms of Subvalvular Aortic Stenosis

The symptoms of SAS may be mild, moderate, or severe, and may be present at birth or appear in the first year of a pet’s life. There may not be any symptoms in milder cases. In moderate or severe cases, symptoms may include:

• Lethargy
• Weakness
• Exercise intolerance
• Coughing or difficulty breathing (may be symptoms of congestive heart failure)
• Fainting/collapse
• Sudden death

Contact your veterinarian at the first appearance of symptoms. A pet who is having difficulty breathing or suddenly collapses is in need of immediate veterinary attention.

Treatment for Subvalvular Aortic Stenosis

Your veterinarian will diagnose SAS through a discussion of symptoms, a physical examination (which will include listening for a heart murmur or irregular heartbeat), and a series of tests.

Testing may include chest x-rays if the pet is having difficulty breathing, an electrocardiogram (ECG) to assess the heart’s electrical activity and any heartbeat irregularities, and an echocardiogram, which can provide definitive diagnosis of the condition. An echocardiogram is an ultrasound that displays an image of the pet’s heart in real-time. The veterinarian (or veterinary cardiologist) uses this image to look for signs of SAS, including valve narrowing, severity of obstruction, heart pressure, and blood flow pattern.

Treatment will ultimately depend on the severity of your pet’s condition. In mild cases, treatment may not be necessary, but your veterinarian may recommend follow-up examinations. In moderate or severe cases, treatment options include:

• Medications: Medications called beta blockers are the most common form of treatment for SAS. Beta blockers (such as atenolol) work to reduce the heart’s workload, slow the heart rate, and regulate heart rhythm.
  
  
• Surgery: Surgery to remove the extra tissue below the aortic valve is an option in severe cases, but it is relatively uncommon. It does not improve the pet’s survival time any more than beta blockers, and as such, medication is the preferred option.
  
  
• Balloon Valvuloplasty: This procedure involves threading a catheter into the narrowed area of the heart. The catheter has a balloon on the end of it, and when the balloon is inflated, it breaks down the extra tissue below the aortic valve and thus dilates the area, resulting in better blood flow. Like surgery, survival time is similar to that seen in pet’s taking beta blockers, and medication is preferred.
  
  
• Limit Exertion: Monitor your pet to ensure that they are not engaging in activities that will increase the heart’s workload. Limit exercise, curb excitable outbursts, and avoid hot or humid weather.

Because SAS is an inherited condition, do not breed affected pets -- even those with mild cases.

More on Heart Health

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7 Risk Factors For Congestive Heart Failure In Dogs