Subaortic Stenosis

What is a Subaortic Stenosis ?

Dogs with SAS have a narrow region of tissue just below the aortic valve that causes an acceleration of blood flow. This abnormal blood flow is what causes the heart murmur. Because the outflow tract is abnormally narrowed, the pressure the left ventricle (pumping chamber) must overcome to pump blood through the aorta (out to the body) is elevated. This change in pressure is termed the pressure gradient – the degree of elevation of the pressure gradient is how SAS is classified. The left ventricular muscle thickens in order to overcome the increase in pressure. The thickened muscle is inadequately perfused by the coronary circulation and becomes damaged. This damaged heart muscle can cause rhythm disturbances and also eventually lead to congestive heart failure.

In normal dogs, the pressure gradient across the aortic valve is less than 20mmHg. In dogs with mild SAS, the pressure gradient is between 20 and 50mmHg. Dogs with moderate SAS have a pressure gradient between 50 and 80mmHg and dogs with severe SAS have a pressure gradient greater than 80mmHg.

Monitor & Treatment

Monitor

Echocardiogram: An echocardiogram is used to make the diagnosis of SAS and to classify its severity. Many dogs with SAS also have aortic insufficiency (leaky aortic valve) as well as an abnormally formed mitral valve (mitral valve dysplasia). Dogs with mild SAS have a good prognosis and generally live a full life.

Dogs with moderate to severe SAS typically demonstrated clinical signs including exercise intolerance and syncope (collapse with exercise). Dogs with moderate SAS have a good prognosis in the short term and fair to good long term. A small percentage of dogs with moderate SAS die suddenly. Dogs with severe SAS are at a high risk for sudden death.

Treatment

There is no definitive therapy for SAS. Medical therapy with a beta blocker appears to reduce the incidence of sudden death in dogs with severe SAS. Interventional therapy (cutting balloon) has also been described as a palliative treatment in patients with severe clinical signs.

Long term monitoring includes echocardiography to assess cardiac function, as well as Holter monitoring to assess for rhythm abnormalities.

Tests & Treatment

Tests

Physical Examination

Dogs with a PDA have a characteristic loud and continuous heart murmur on the left side of their chest

Echocardiography (Heart Ultrasound)

Echocardiography is the best way to image and measure the PDA. Echocardiography is a non-invasive ultrasound examination that allows the cardiologist to closely evaluate the heart chambers and valves.

Treatment

PDA is repairable with an interventional or surgical procedure. Most pets are candidates for a catheterbased interventional occlusion of the defect, which can be performed without thoracotomy (opening the chest). A small incision is made in the skin to allow a catheter to be placed in the femoral artery. A specialized form of x-ray, called fluoroscopy is used to guide the catheter into the PDA and deploy a device called an ACDO in the defect. The device occludes the PDA, and has a very high success rate and low complication rate. Your pet will be monitored overnight following the procedure and will go home the next day. Pets with a successfully occluded PDA with live a normal life expectancy!

Frequently Asked Questions

What causes SAS?

SAS is typically a genetic condition present at birth. It is more common in certain breeds, especially large and giant breed dogs.

Which dogs are at risk?

Breeds commonly affected include Golden Retrievers, Boxers, Newfoundlands, German Shepherds, and Rottweilers.

What are the signs of SAS?

Signs can vary depending on severity and may include:

Heart murmur (often detected on routine exam)
Exercise intolerance
Fainting (syncope) or collapse with activity
Lethargy
In severe cases, sudden death

Some dogs show no outward signs early in the disease.

Can SAS be cured?

There is no cure, but treatment and monitoring can help manage the condition and reduce risks.

How Do I Schedule?

Please call us at 720-510-7707 to book a consultation.