What Is Subaortic Stenosis?

Subaortic stenosis (SAS) refers to the narrowing of the area of the heart just below the aortic valve. The narrowing develops due to the presence of abnormal fibrous tissue and causes the increase of blood pressure in the left ventricle. This is the third most common congenital genetic heart defect in dogs.

Susceptible Dog Breeds

Breeds predisposed include:

• Bernese Mountain Dog
• Bouvier des Flandres
• Boxer
• Bull Terrier
• German Shepherd
• Golden Retriever
• Newfoundland
• Rottweiler

An unusual form of subaortic stenosis in combination with mitral valve dysplasia has been reported in the Golden Retriever. Systematic studies of familial subaortic stenosis in Newfoundland dogs have demonstrated that the stenosis development has a specific pattern of heredity.⁹

Signs & Symptoms

While most affected dogs have no signs, some animals may experience episodes of fainting and difficulty breathing. Affected puppies may have stunted growth, weakness, shortness of breath, abdominal swelling and, in extreme instances, may die suddenly within the first month of life. Most SAS patients are diagnosed when a heart murmur is detected at the left heart base during a routine physical examination.

Treatment

Prognosis and therapy depend on the severity of the disease and complications that may be present. Treatment is directed towards decreasing the workload on the diseased heart. Surgical correction of the defect may be attempted, yet owing to the nature of the disease and the age of the affected dog, the outcome of such a procedure is generally poor.

Cardiopulmonary bypass and open-heart surgery are necessary to reach the stenotic area directly. Although this type of surgery can significantly reduce the ventricular pressure and possibly improve exercise ability, no improvement in long-term survival was found compared to dogs not undergoing the procedure.⁷ Atenolol, a specific adrenergic drug, has been used to prevent sudden death in dogs with severe subaortic stenosis.

Prognosis

The majority of severely affected dogs with SAS die suddenly before the age of three years. However, the increasing availability of modern diagnostic imaging systems now allows a better assessment of cardiac function, thereby facilitating early detection of the disease. Dogs with mild pressure rarely progress to congestive heart failure (CHF). If CHF develops, it can be managed with medications that can prolong life and improve its quality.

Dogs with a mild form of the disease and those who develop infective endocarditis are usually diagnosed at older ages than those with moderate and severe forms. Sudden death occurs mainly in the first three years of life with severe obstruction. Infective endocarditis and left heart failure tend to occur later in life and in dogs with mild to moderate obstructions.

Terms

• Stenosis
  • Constriction
• Subaortic Stenosis
  • Barrowing of the area of the heart below the aortic valve
• Ventricle
  • The lower chamber of the heart
• Dysplasia
  • Developmental abnormality

References:

• Falk et al. – Intramyocardial Arterial Narrowing In Dogs With Subaortic Stenosis – J Small Anim Pract. 2004 Sep;45(9):448-53
• Robert M. Freedom, Shi-Joon Yoo, Haverj Mikailian, William G. Williams – The Natural And Modified History Of Congenital Heart Disease
• O. M. Radostits, Ian G. Mayhew, Doreen Marie Houston – Veterinary Clinical Examination And Diagnosis
• Jim E. Riviere, Mark G. Papich – Veterinary Pharmacology And Therapeutics
• John K. Dunn – Textbook Of Small Animal Medicine
• Chris C. Pinney – German Shorthaired Pointer
• Richard W. Nelson, C. Guillermo Couto – Small Animal Internal Medicine
• Matthew J. Ryan, Veterinary Hospital Section Of Cardiology, UPENN – Understanding Canine Subaortic Stenosis
• Siew Yen Ho, Magnus Michaëlsson – Congenital Heart Malformations in Mammals