Aortic stenosis in cats

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Aortic (subaortic) stenosis is a narrowing of the pathway for blood leaving the heart. The narrowing is usually beneath the aortic valve of the left ventricle; the condition is then called subvalvular aortic stenosis or SAS for short. SAS is a genetically predetermined disease that rarely affects cats, and usually leads to hypertrophic cardiomyopathy. The mode of inheritance, or the genetic cause, is not simple and healthy carriers of the disease genes are common.

Mild cases of SAS have little impact other than causing a heart murmur and rendering the cat unsuitable for breeding. Moderate to severe cases are at risk for exercise intolerance, fainting, heart failure, irregular heart rhythms, infections on the heart valve and sudden death.

Symptoms

The presence of a murmur (especially in breeds at risk (Main Coon, Persian and American Shorthair)), easily fatigued, cough, difficult breathing, collapsing, fainting, illness with fever. Aortic stenosis may have a heritable basis, possibly aberrant genes encoding for altered sarcomeric proteins.

Diagnosis

Diagnostic tests are needed to recognize SAS and exclude other diseases. Tests may include: Complete medical history and physical examination, including examination with a stethoscope (cardiac auscultation), an echocardiogram (ultrasound of the heart) with Doppler is needed to make a definitive diagnosis. On echocardiographs, left ventricular hypertrophy is seen (diastolic dimension of the interventricular septum and/or LV posterior wall greater than 6 mm). A subvalvular or supravalvular fibrous ridge may be identified. In some cases, left atrial enlargement may be present. Doppler study of the left ventricular outflow reveals increased ejection velocity of blood flow (> 2.0 m/s).

An electrocardiogram (EKG) or a 24-hour electrocardiogram (Holter EKG) may be recommended to identify abnormal heart rhythms. Secondary hypertrophic cardiomyopathy can, and does, occur in cats with valvular (aortic) stenosis. When selective interventricular septal thickening causes partial left outflow obstruction, ejection through the narrowed outflow tract results in turbulence that, in essence, "sucks" the anterior mitral valve leaflet into the ejection flow; this further impedes ejection and exacerbate mitral regurgitation and its effects.

Treatment

For mild cases, there is no treatment. For more serious cases, treatments for SAS may include one or more of the following: Surgery and cardiac catheterization procedures have been used to dilate or cut out the affected area; however, these procedures do not significantly increase long-term survival. Drugs called beta-blockers, such as propranolol, atenolol and metoprolol, are often prescribed to protect the heart muscle and reduce irregular heartbeats. Drugs for heart failure may be prescribed should an irregular heartbeat develop.

Home Care and Prevention

If your dog has SAS, find out the degree of severity so you can modify your dog's activity. Mild cases of SAS pose no real activity/exercise limitations, but more advanced cases may require some exercise restriction or medical therapy. Learn to measure your dog’s rectal temperature. If your dog is acting sick and has a fever (temperature greater than 103), call your veterinarian immediately. Schedule regular examinations (every 6 to 12 months) and possibly chest X-rays and/or an echocardiogram. Breeders should have their dogs screened for SAS. Never breed a dog with congenital heart disease.