What is subaortic stenosis (SAS) in dogs?

Subaortic stenosis in dogs is a congenital condition that involves a narrowing of the aortic valve in the heart. There are three types of aortic stenosis: valvular, supravalvular, and the most common, subvalvular. Blood flows from the left ventricle through the aortic valve to the rest of the body. When the valve is narrow, it becomes harder for the blood to flow, leading to increased pressure. This puts extra strain on the heart, causing it to contract more strongly in pets affected with SAS. Over time, this can result in the heart wall becoming thicker and potentially lead to arrhythmias or congestive heart failure, which occurs when blood cannot be properly supplied to the body.

Subaortic stenosis is commonly diagnosed in young puppies between the ages of 6 months and a year. It is often discovered accidentally during a physical examination when the veterinarian listens to the dog's heart and hears a murmur. If the stenosis is not severe, there may not be any noticeable symptoms. However, if it has progressed to congestive heart failure, it can be detected through an ultrasound scan after the dog begins exhibiting symptoms such as shortness of breath.

Treatment for subaortic stenosis is generally based on the results of the dog’s cardiac function evaluation and the symptoms. It may involve the prescription of medication, and in some cases, correction can be achieved through surgery or interventional procedures. The prognosis for this condition varies depending on the severity of the stenosis.

Causes of subaortic stenosis (SAS) in dogs

There is evidence to suggest that subaortic stenosis may be hereditary in some dog breeds. However, the exact cause has yet to be determined. This condition has been reported in various breeds, particularly in larger dogs, and tends to worsen as the dog ages.

It can occur in any breed of dog, but known predisposing breeds include:

• Newfoundlands
• Golden Retrievers
• Rottweilers
• Boxers
• German Shepherds
• Bouvier des Flanders
• Bernese Mountain Dogs
• Bordeaux Mastiffs

Symptoms of subaortic stenosis (SAS) in dogs

Subaortic stenosis is classified into three stages: mild, moderate, and severe, depending on the degree of stenosis observed in an echocardiograph. The symptoms may vary, depending on the severity of the stenosis.

• Mild

  There are usually no symptoms and your pet can typically lead a normal life.

• Moderate to severe

  During the moderate and severe stages of the condition, fibrous ridges are often visible on echocardiography. As the myocardium thickens over time, arrhythmias and congestive heart failure may develop, causing symptoms such as weakness, coughing, shortness of breath, decreased ability to exercise, and in some cases, fainting.

Risk of subaortic stenosis (SAS) in dogs

Since there is evidence that subaortic stenosis is genetic, caution should be exercised in cases where one or both parents has a history of heart disease or is on the list above of breeds. If your dog's breathing rate exceeds 40 breaths per minute while sleeping or resting, it is recommended that you take them to a veterinary hospital for testing. If symptoms such as coughing, shortness of breath, or fainting occur, an examination by a veterinarian is highly suggested.

Countermeasures against subaortic stenosis (SAS) in dogs

The treatment of subaortic stenosis in dogs varies based on the severity and symptoms, so it is important to consult a specialized veterinary hospital for proper treatment. If you are observing symptoms related to heart disease, it is advisable to restrict excessive exercise or activity and provide a calm environment for your dog until you can visit a veterinarian for diagnosis.

Diagnosing canine subaortic stenosis (SAS)

If a dog is suspected of having heart disease, the veterinarian will assess the pet for early signs of the condition, such as exercise intolerance, shortness of breath, and coughing.

The following tests can be performed:

• Physical examination

  Auscultation is an essential component of a physical examination for dogs exhibiting symptoms related to heart disease. It helps in detecting heart murmurs or arrhythmias in case the dog is suffering from heart disease by listening to the heart rate.

• X-rays

  If you notice symptoms such as shortness of breath or coughing in your dog, a chest X-ray can be performed to differentiate it from other respiratory diseases and determine if it is a result of heart disease. During the examination, the size of the heart will also be evaluated. In the case of subaortic stenosis, the left side of the heart may appear enlarged.

• Electrocardiograms (ECG)

  An electrocardiogram (ECG) is used to evaluate the electrical activity of a heart. Electrodes are attached to the body to determine the presence and type of arrhythmias. In cases of subaortic stenosis, the ECG may appear normal. However, if the disease has progressed, the height of the R wave may increase and there may be evidence of ischemic changes in the myocardium that indicate SAS.

• Echocardiography

  It is the most useful method for diagnosing heart disease in dogs. This test provides a direct examination of the internal structure of the heart, allowing for a thorough evaluation of its structure and function. This includes assessments of the presence and severity of any blockages, blood flow, velocity, pressure differences, and the thickness of the heart's wall.

  In the case of subaortic stenosis, a fibrous ridge is observed around the aortic valve and the left ventricular wall may appear thick or the left atrium may be dilated. The prognosis may be poor if there is a pressure difference of 80mmHg or more when measuring the blood velocity and pressure difference passing through the aortic valve.

• Blood tests

  Blood tests, including a total blood count, serum chemistry, and electrolyte analysis, are conducted following the diagnosis of heart disease. This is to assess any potential side effects and to evaluate the overall condition of the body before medication is prescribed. Although not frequently utilized for subaortic stenosis, biomarkers such as ProBNP or Troponin I, which indicate the presence of heart disease, may be included in the blood tests, depending on the circumstances.

How to treat subaortic stenosis (SAS) in dogs

In the case of mild subaortic stenosis in dogs, no treatment is necessary. Dogs with mild subaortic stenosis in dogs can lead a normal life, and only periodic monitoring should be advised. However, if the stenosis worsens during growth and becomes moderate or severe, treatment and management may be necessary. As heart disease is challenging to cure, the objective of treatment is to relieve symptoms and prevent further deterioration.

The following treatments can be performed for moderate to severe SAS in dogs:

• Exercise restrictions

  To minimize the work of the heart, it is necessary to limit movement and be careful not to overexcite dogs with SAS.

• Medication

  Beta-blockers are utilized for the pharmaceutical treatment of subaortic stenosis, which curbs the heart from beating excessively fast and regulates arrhythmias. In the event of congestive heart failure, drugs such as diuretics can decrease fluid buildup in the heart or lungs.

• Interventional and surgical procedures

  To effectively address the issue of subaortic stenosis, several surgical techniques and minimally invasive therapies, such as balloon catheterization, can be employed to enlarge the affected region. However, access to these procedures or surgeries is often limited, so it is crucial to seek consultation with a specialist.

Prevention of subaortic stenosis (SAS) in dogs

Since subaortic stenosis is a congenital disease present from birth, it cannot be prevented. It is advisable to detect heart problems early through regular check-ups to prevent further progression of symptoms. If your dog has a genetic condition such as subaortic stenosis, it is recommended not to breed to prevent passing it on to future generations.

Find out more about your dog’s symptoms and diseases on the Buddydoc app!

The Buddydoc library is filled with everything you’d want to know about each symptom and disease your pet may experience. If you would like to find out more about the causes, signs, treatments, preventions, and more for your dog’s disease. Try out the Buddydoc app and search your pet’s symptom or disease in the Buddydoc library.