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Aortic Stenosis

Aortic Stenosis: An Overview

Aortic Stenosis (AS) is a narrowing just above the aortic valve in the heart, or (rarely) of the actual valve. This narrowing causes partial obstruction of blood flow from the left ventricle of the heart through the aortic valve and into the aorta. Subvalvular Aortic Stenosis is the most common form of AS where the defect is located just below the aortic valve. The defect or narrowing is usually caused by abnormal formation of nodules or a fibrous ridge or ring of tissue. The heart must work harder to pump enough oxygenated blood through the stenosed part. AS may be mild and not affect the quality or longevity of the dog's life or it may be severe. A severe defect can significantly compromise the outflow of oxygenated blood to the brain and other vital organs and can cause fainting, collapse and sudden death. Several breeds are predisposed to AS, including Golden Retrievers, Newfoundlands, Boxers, German Shepherds, Rottweilers, Shar-Pei, Bull Terriers, English Bulldogs and Bouvier de Flanders.

Causes of Aortic Stenosis

Aortic stenosis is hereditary. It is not possible to predict the severity of the defect from one generation to the next so breeding a dog with mild aortic stenosis could produce puppies with severe aortic stenosis. Thus, it is recommended that affected dogs not be used in a breeding program.

Prevention of Aortic Stenosis

Because AS is hereditary, prevention of AS in dogs is focused on breeding practices. Dogs should be tested by a board-certified cardiologist prior to breeding. Dogs with clear screening, including Doppler studies, after 12 months of age are considered "clear."

Symptoms of Aortic Stenosis

Symptoms can occur as a direct result of AS or secondary to left ventricular hypertrophy (thickening). This can lead to abnormal heart rhythms and compromise the delivery of oxygenated blood from the left ventricle through the aortic valve and into the aorta. Symptoms may include:

Exercise intolerance
Cough
Difficulty breathing
Illness with fever
Fainting (Syncope) - this happens when there is lack of oxygen to the brain; stress or exertion can cause fainting.
Sudden Death - if the heart goes into a state of where it is pumping too quickly (ventricular tachycardia), collapse and sudden death may occur.

Diagnosing Aortic Stenosis

Diagnosing AS in dogs involves a screening called auscultation where the veterinarian listens to the dog's heart to see if there is heart murmur. Murmurs in absence of any other clinical signs are often picked up on routine annual exams. If a heart murmur is detected, a referral to a cardiologist may be made.
Murmurs are graded according to severity as follows:

0/6 murmurs: This grade is considered to be "mild".
1/6 and 2/6 murmurs: These dogs are considered to be unlikely to develop symptoms.
3/6 and 4/6 murmurs: This grade is termed "moderate" with majority of dogs still being unlikely to develop symptoms; however, a small number will become symptomatic.
5/6 and 6/6 murmurs: This grade is considered to be "severe"; dogs in this category are most at risk to develop symptoms.

If other diagnostic tests are warranted, your veterinarian may prescribe other non-invasive tests, including:
X-ray: This is to look at the size and shape of the heart is performed. An X-ray can identify any abnormal enlargement of the heart chambers, which could indicate severe AS.
Electrocardiogram (EKG): This is used to measure the electrical impulses to the heart and test for PVC (premature ventricle contractions) or abnormal heart rhythms.
Ultrasound: Ultrasound can measure the internal dimensions of the heart, including the thickness of the left ventricle wall, which becomes thickened in sever AS.
Doppler: Doppler can measure the speed of blood flow (aortic outflow velocity) through the valves, specifically from the left ventricle through the aortic valve into the aorta. It has been reported that if the blood flow velocity is less than 4 meters/second at maturity, the dog usually will have a normal quality and quantity of life. However, if the blood flow velocity is measured to be greater than 5 meters/second, the dog will usually succumb to the disease. This is the best and most accurate test as an affected dog's electrocardiogram (EKG) is usually normal and radiographs are frequently normal in affected dogs as well.
Note: if you own a breed that is particularly susceptible to inheriting AS, ask your veterinarian for a referral to a specialist for a baseline exam.

Treating Aortic Stenosis

In mild cases of AS there is no specific treatment. However, veterinarians recommend that dogs with AS avoid strenuous exercise, especially in hot weather, and maintain a healthy weight.
For more severe cases treatment may include:

Surgery and cardiac catheterization: These procedures have been used to dilate or cut out the affected area; however, these procedures do not significantly increase long-term survival.
Beta-blockers: These drugs, including propranolol, atenolol and metoprolol, are used to protect the protect the heart muscles and reduce irregular heartbeats. Other drugs for heart failure may be prescribed should an irregular heartbeat develop. Beta-blockers may be prescribed for dogs with severe AS, evidence of left ventricular hypertrophy or evidence of VPCs (ventricular premature contractions, or heart rhythm disturbances). Beta-blockers help to improve exercise tolerance, reduce cardiac (heart) workload and prevent abnormal heart rhythms.

Care for Dogs with Aortic Stenosis

In the majority of cases, development of the defect does not usually progress beyond puppyhood. In other words, the grading of the heart murmur would be unchanged from the age of 1 to 2 years throughout the rest of the dog's life. However, in a small number of dogs (estimated to be about 10% of those affected) the defect appears to get progressively worse over the years. This certainly gives weight to the argument that annual auscultation should be considered in those breeds known to be affected by AS.

If your dog has AS, find out the severity of the disease by having your veterinarian perform diagnostic tests. Once you know the severity, there are things you can do to protect your dog's health:
Modify your dog's activity: If AS is mild, no activity/exercise limitations may be necessary, but if AS is more advanced, some exercise restriction is necessary.
Measure your dog's rectal temperature: If your dog is acting sick and has a fever (temperature greater than 103), call your veterinarian immediately.
Schedule regular examinations (every 6 to 12 months) and possibly chest X-rays and/or an echocardiogram.

The AKC Canine Health Foundation and Aortic Stenosis

Six grants to study aortic stenosis have been funded by CHF. The grants look to increase the current knowledge about the inheritance, genetic causes and potential treatment of aortic stenosis.

Help Future Generations of Dogs

Participate in canine health research by providing samples or by enrolling in a clinical trial. Samples are needed from healthy dogs and dogs affected by specific diseases.