What is aortic stenosis?
Aortic stenosis is a heart disease that is more common in certain dog breeds. Aortic stenosis describes a narrowing at the aortic valve of the heart. The aortic valve is the valve through which blood leaves the heart, traveling to the rest of the body. When this valve is narrowed, the heart (and specifically the left ventricle, which is the chamber that pumps blood through the aorta) must work harder to force blood out through the valve. This additional work can have a number of harmful effects on the heart, leading to muscle failure and other complications.
Aortic stenosis can occur within the valve (valvular aortic stenosis), just above the valve (supravalvular aortic stenosis), or just below the valve (subvalvular or subaortic stenosis). Subaortic stenosis (SAS) is the most common of these conditions in dogs.
Aortic stenosis is a hereditary condition that occurs in certain breeds. The dog breeds most commonly affected by aortic stenosis include the Newfoundland, Boxer Dog, Rottweiler, Golden Retriever, and Dogue de Bordeaux. Other breeds in which aortic stenosis has been reported, although less commonly, include the Bull Terrier, English Bulldog, German Shepherd, German Shorthaired Pointer, Great Dane, Mastiff, and Samoyed.
What are the clinical signs of aortic stenosis?
In many cases, affected dogs do not show any signs. Aortic stenosis is often initially detected on a routine physical examination, when the veterinarian notices a heart murmur. In moderate to severe cases, signs may be noted at birth; in mild cases, the murmur may not be noted until the dog is 6-12 months old.
In dogs with severe disease, you may observe signs related to heart dysfunction. These signs include lethargy, exercise intolerance, shortness of breath, and fainting. These signs are typically related to the heart’s inability to circulate blood effectively.
Signs of heart failure may also be seen in severe cases of aortic stenosis. These signs include coughing, increased breathing effort, and open-mouth breathing. In heart failure, fluid begins to the pool in the lungs; the signs of heart failure are associated with this fluid accumulation. Heart failure is more common in dogs that have other heart valve problems occurring at the same time, but can be seen with aortic stenosis alone.
"Signs of heart failure may also be seen in severe cases of aortic stenosis."
In some severe cases, aortic stenosis can lead to changes in the structure of the heart muscle. These changes can influence how the heart conducts electrical signals. This can lead to a risk of sudden death, if the heart muscle becomes unable to effectively conduct the electrical impulses that trigger the heart to beat.
How is aortic stenosis diagnosed?
On examination, your veterinarian will typically hear a heart murmur in an area of the chest that is associated with aortic stenosis. A murmur in this area, especially in a large-breed dog, strongly suggests aortic stenosis.
The tests most commonly used to confirm a diagnosis of aortic stenosis include chest radiographs (X-rays), electrocardiography (ECG), and echocardiogram (ultrasound of the heart).
- Chest radiographs (X-rays) may look normal early in the course of disease, or in dogs that are only mildly affected. In more severe cases, however, radiographs often show enlargement of the left side of the heart and a visible bulge of the aorta.
- ECG is often normal in affected dogs. In some cases, however, ECG can identify arrhythmias or enlargement of the left ventricle of the heart.
- Echocardiology is the most sensitive test for diagnosing aortic stenosis. On echocardiogram, a fibrous band of tissue can often be seen at the aortic valve. Color-flow Doppler (a test that assesses the motion of the blood in the heart) can be used to observe turbulent blood flow through that region of the heart.
Routine laboratory tests (complete blood cell count, serum biochemistry, and urinalysis) will often be performed to assess your dog’s overall health. These tests are normal in most affected dogs, though mild changes may sometimes be observed. Having baseline laboratory values will allow your veterinarian to monitor your dog, especially if medications must be used.
How is aortic stenosis treated?
In mild cases of aortic stenosis, treatment is typically not required. Your dog may be closely monitored for signs of disease progression, but medication is not typically needed.
In moderate to severe cases, long-term medication may be required. Beta blockers can be used to slow the heart rate, allowing the heart to work more efficiently. In some cases, hospitalization may be required for the initial stabilization of clinical signs associated with aortic stenosis.
Surgical procedures have also been considered and evaluated for use in aortic stenosis, including the use of a 'cutting' balloon that is inserted into the heart via catheterization and used to break down the tissue causing the constriction. This surgery is not commonly performed, but may be an option depending on the severity of your dog's disease and your access to specialists who are familiar with the procedure.
Exercise should be restricted in dogs with aortic stenosis, especially those with severe disease. The most significant health risk associated with aortic stenosis is sudden death. While this sudden death is not always correlated with exercise, strenuous exercise does appear to make it more likely.
"Exercise should be restricted in dogs with aortic stenosis, especially those with severe disease."
Given the genetic basis of aortic stenosis, affected dogs should not be bred.
What is the prognosis for aortic stenosis?
Echocardiography can be beneficial for developing a prognosis for each individual patient.
Pressure differentials across the valve (the difference in pressures between the two sides of the valve, which can be measured with echocardiography) are directly correlated with the risk of sudden death. Dogs with a high pressure differential are at a high risk of sudden death within the next year, while dogs with a low pressure differential are at a low risk of sudden death.