28 Mar Subaortic Stenosis (SAS) in Dogs
A seemingly harmless heart murmur could be the first sign of a life-threatening condition called subaortic stenosis in dogs. Subaortic stenosis (SAS) is a serious congenital heart condition that primarily affects large and giant dog breeds. Though it may go unnoticed at first, early signs—like heart murmurs—can offer the first clue that something is wrong.
This article explains what SAS is, how it progresses, which breeds are at risk, and what treatment options are available. Understanding SAS is essential for dog owners, breeders, and veterinarians alike, as early detection and proper management can make a significant difference in a dog’s quality of life and longevity.
What is Subaortic Stenosis?
Subaortic stenosis (SAS) is a congenital heart defect characterized by a fibrous or scar-like narrowing of the left ventricular outflow tract (LVOT) just below the aortic valve. This narrowing forces the left ventricle to work harder to pump blood through the restricted area, leading to increased pressure, turbulent blood flow, and an audible heart murmur.
It’s important to understand that while heart murmurs are often the first clue to SAS, not all murmurs indicate heart disease. Any condition that creates turbulent blood flow can generate a murmur, but further diagnostics are needed to confirm whether the cause is SAS or a benign murmur.
Breeds at Risk
SAS is a hereditary condition and is most commonly seen in large and giant breeds. Breeds predisposed to SAS include:
- Golden Retriever
- Rottweiler
- Newfoundland
- Great Dane
- Boxer
- German Shepherd
- German Shorthaired Pointer
- Dogue de Bordeaux
Because inheritance patterns are complex, even dogs with mild SAS can produce offspring with severe disease, making screening and responsible breeding essential.
How Subaortic Stenosis in Dogs Progresses Over Time
Puppies with SAS are typically born with only a small ridge of fibrous tissue near the aortic valve. However, the disease progresses rapidly within the first 6 to 12 months of life. As the narrowing worsens:
- The heart murmur becomes louder and more distinct.
- The left ventricle undergoes hypertrophy (thickening of the muscle wall) due to the increased workload.
- Over time, the thickened ventricle becomes stiffer and less flexible, impairing its ability to fill properly.
- Changes in heart muscle structure can disrupt electrical conduction, leading to arrhythmias (irregular heartbeats).
- Severe cases can result in fainting (syncope) or sudden death, particularly during exercise or excitement.
- Dogs with mild SAS may live normal lifespans, while those with severe disease often do not survive beyond three years without treatment.
Complications Associated with Subaortic Stenosis in Dogs
Dogs with SAS are at an increased risk for:
- Cardiac arrhythmias – Abnormal electrical activity can cause fainting or sudden cardiac death.
- Congestive heart failure – The heart struggles to maintain normal circulation as the disease progresses.
- Bacterial endocarditis – The abnormal aortic valve structure makes it more susceptible to life-threatening infections from bacteria in the bloodstream.
How SAS is Diagnosed
The gold standard for diagnosing SAS is an echocardiogram with Doppler ultrasound, which provides a detailed image of the heart and measures blood flow velocity across the stenosis.
Key diagnostic measurement: The pressure gradient (difference in pressure across the narrowed area) is used to assess disease severity:
- Mild SAS: Pressure gradient < 40 mmHg – typically does not require treatment.
- Moderate SAS: Pressure gradient 40-80 mmHg – may require treatment based on clinical signs.
- Severe SAS: Pressure gradient > 80 mmHg – carries a high risk of heart failure and sudden death.
Treatment Options for Subaortic Stenosis in Dogs
1. Medical Management (Beta Blockers)
The primary treatment for SAS is the use of beta blockers, such as atenolol, which help:
- Reduce the heart rate, minimizing strain on the left ventricle.
- Decrease the risk of life-threatening arrhythmias.
- Improve blood flow efficiency.
A study found that dogs treated with atenolol had a median survival of 56 months compared to 19 months in untreated dogs.
Because fatal arrhythmias often occur during exercise or excitement, limiting strenuous activity is recommended.
2. Balloon Valvuloplasty
This minimally invasive procedure involves threading a catheter with an inflatable balloon into the heart. Once positioned across the stenotic area, the balloon is inflated to stretch and break down the fibrous tissue.
However, studies show that long-term survival rates for balloon valvuloplasty are similar to those of medical management with atenolol, so it is not currently recommended as a first-line treatment.
3. Open-Heart Surgery
In theory, surgical removal of the fibrous tissue causing the stenosis is possible. However, due to high surgical risk, limited availability, and outcomes similar to medical therapy, open-heart surgery is rarely performed in veterinary medicine.
Prognosis and Long-Term Management
Mild SAS: Dogs with pressure gradients below 40 mmHg typically do not require treatment and can live normal lifespans.
Moderate to Severe SAS: Dogs with pressure gradients above 80 mmHg are at high risk of heart failure and sudden cardiac death.
With atenolol treatment, dogs with SAS can have improved survival, but long-term prognosis depends on disease severity.
The Importance of Screening and Responsible Breeding
Since SAS is hereditary, affected dogs should not be bred, even if their disease is mild. Selective breeding and early screening in predisposed breeds are crucial steps in reducing the prevalence of SAS in future generations.
Key Takeaways
- SAS is a progressive congenital heart disease affecting large breed dogs.
- Heart murmurs in puppies may indicate SAS, but further testing is required for diagnosis.
- Echocardiography with Doppler studies is the gold standard for evaluating disease severity.
- Beta blockers (atenolol) improve survival and reduce arrhythmia risk.
- Surgical and interventional procedures do not yet offer better outcomes than medical management.
- Dogs with severe SAS often do not survive beyond three years without treatment.
Final Thoughts
Subaortic stenosis in dogs is a complex but manageable heart condition that can be treated appropriately when diagnosed early. While mild cases may not require intervention, moderate to severe SAS can lead to serious complications if left untreated. With medications like beta blockers and careful activity management, many dogs can live longer, healthier lives.
By staying informed, proactive, and committed to responsible breeding, we can help protect future generations of dogs from the silent danger of subaortic stenosis. Contact us at Animal Cardiology Specialists of Nevada to schedule an appointment for your canine companion.
Images used under creative commons license – commercial use (03/28/2025) Photo by Daniel Kandie on Unsplash