Subaortic Stenosis

Subaortic stenosis (SAS) is a congenital heart defect where a fibrous ridge or ring develops below the aortic valve, creating obstruction to blood flow from the left ventricle. It is the most common congenital heart defect in large-breed dogs. The obstruction creates turbulent flow (murmur) and forces the heart to work harder, leading to left ventricular hypertrophy.

Symptoms & Signs

• Heart murmur (often detected at first vaccination)
• Exercise intolerance
• Syncope (fainting) during exercise
• Sudden death (particularly during exertion)
• Weakness
• Labored breathing

Causes & Risk Factors

Genetic with suspected autosomal dominant inheritance with variable penetrance. The fibrous ridge develops during the first weeks of life and may progress during growth. Breeds most affected: Newfoundland, Golden Retriever, Rottweiler, Boxer, German Shepherd.

Diagnosis

Cardiac auscultation (systolic murmur loudest at left heart base). Echocardiography measures pressure gradient across the stenosis and assesses severity (mild <50 mmHg, moderate 50-80, severe >80 mmHg). Doppler assessment of flow velocity.

Treatment

Mild cases: monitoring and exercise restriction. Beta-blockers (atenolol) to reduce myocardial oxygen demand and arrhythmia risk. Balloon valvuloplasty or cutting balloon for severe cases (limited long-term benefit). Avoidance of strenuous exercise.

Prevention

Cardiac screening of breeding stock with echocardiography. Removing affected dogs and their parents from breeding programs. Screening puppies before sale. Genetic research ongoing.

Prognosis

Mild SAS: normal lifespan with monitoring. Moderate: reduced lifespan, risk of sudden death. Severe (gradient >80 mmHg): median survival 3-5 years, high risk of sudden death, endocarditis, and heart failure.

Affected Breeds (5)

Related Conditions

• Aortic Stenosis
• Endocarditis
• Ventricular Arrhythmias